NASKAR: 05/01/06

Java Questions:

1. What is a transient variable?
A transient variable is a variable that may not be serialized.

2. Which containers use a border Layout as their default layout?
The window, Frame and Dialog classes use a border layout as their default layout.

3. Why do threads block on I/O?
Threads block on I/O (that is enters the waiting state) so that other threads may execute while the I/O Operation is performed.

4. How are Observer and Observable used?
Objects that subclass the Observable class maintain a list of observers. When an Observable object is updated it invokes the update() method of each of its observers to notify the observers that it has changed state. The Observer interface is implemented by objects that observe Observable objects.

5. What is synchronization and why is it important?
With respect to multithreading, synchronization is the capability to control the access of multiple threads to shared resources. Without synchronization, it is possible for one thread to modify a shared object while another thread is in the process of using or updating that object's value. This often leads to significant errors.

6. Can a lock be acquired on a class?
Yes, a lock can be acquired on a class. This lock is acquired on the class's Class object.

7. What's new with the stop(), suspend() and resume() methods in JDK 1.2?
The stop(), suspend() and resume() methods have been deprecated in JDK 1.2.
8. Is null a keyword?
The null value is not a keyword.

9. What is the preferred size of a component?
The preferred size of a component is the minimum component size that will allow the component to display normally.

10. What method is used to specify a container's layout?
The setLayout() method is used to specify a container's layout.

11. Which containers use a FlowLayout as their default layout?
The Panel and Applet classes use the FlowLayout as their default layout.

12. What state does a thread enter when it terminates its processing?
When a thread terminates its processing, it enters the dead state.

13. What is the Collections API?
The Collections API is a set of classes and interfaces that support operations on collections of objects.

14. which characters may be used as the second character of an identifier, but not as the first character of an identifier?
The digits 0 through 9 may not be used as the first character of an identifier but they may be used after the first character of an identifier.
15. What is the List interface?
The List interface provides support for ordered collections of objects.

16. How does Java handle integer overflows and underflows?
It uses those low order bytes of the result that can fit into the size of the type allowed by the operation.

17. What is the Vector class?
The Vector class provides the capability to implement a growable array of objects

18. What modifiers may be used with an inner class that is a member of an outer class?
A (non-local) inner class may be declared as public, protected, private, static, final, or abstract.

19. What is an Iterator interface?
The Iterator interface is used to step through the elements of a Collection.

20. What is the difference between the >> and >>> operators?
The >> operator carries the sign bit when shifting right. The >>> zero-fills bits that have been shifted out.

21. Which method of the Component class is used to set the position and size of a component?
setBounds()
22. How many bits are used to represent Unicode, ASCII, UTF-16, and UTF-8 characters?
Unicode requires 16 bits and ASCII require 7 bits. Although the ASCII character set uses only 7 bits, it is usually represented as 8 bits. UTF-8 represents characters using 8, 16, and 18 bit patterns. UTF-16 uses 16-bit and larger bit patterns.

23 What is the difference between yielding and sleeping?
When a task invokes its yield() method, it returns to the ready state. When a task invokes its sleep() method, it returns to the waiting state.

24. Which java.util classes and interfaces support event handling?
The EventObject class and the EventListener interface support event processing.

25. Is sizeof a keyword?
The sizeof operator is not a keyword.

26. What are wrapper classes?
Wrapper classes are classes that allow primitive types to be accessed as objects.

27. Does garbage collection guarantee that a program will not run out of memory?
Garbage collection does not guarantee that a program will not run out of memory. It is possible for programs to use up memory resources faster than they are garbage collected. It is also possible for programs to create objects that are not subject to garbage collection.

28. What restrictions are placed on the location of a package statement within a source code file?
A package statement must appear as the first line in a source code file (excluding blank lines and comments).
29. Can an object's finalize() method be invoked while it is reachable?
An object's finalize() method cannot be invoked by the garbage collector while the object is still reachable. However, an object's finalize() method may be invoked by other objects.

30. What is the immediate superclass of the Applet class?
Panel

31. What is the difference between preemptive scheduling and time slicing?
Under preemptive scheduling, the highest priority task executes until it enters the waiting or dead states or a higher priority task comes into existence. Under time slicing, a task executes for a predefined slice of time and then reenters the pool of ready tasks. The scheduler then determines which task should execute next, based on priority and other factors.

32. Name three Component subclasses that support painting.
The Canvas, Frame, Panel, and Applet classes support painting.

33. What value does readLine() return when it has reached the end of a file?
The readLine() method returns null when it has reached the end of a file.

34. What is the immediate superclass of the Dialog class?
Window.

35. What is clipping?
Clipping is the process of confining paint operations to a limited area or shape.
36. What is a native method?
A native method is a method that is implemented in a language other than Java.

37. Can a for statement loop indefinitely?
Yes, a for statement can loop indefinitely. For example, consider the following:
for(;;) ;

38. What are order of precedence and associativity, and how are they used?
Order of precedence determines the order in which operators are evaluated in expressions. Associatity determines whether an expression is evaluated left-to-right or right-to-left

39. When a thread blocks on I/O, what state does it enter?
A thread enters the waiting state when it blocks on I/O.

40. To what value is a variable of the String type automatically initialized?
The default value of a String type is null.

41. What is the catch or declare rule for method declarations?
If a checked exception may be thrown within the body of a method, the method must either catch the exception or declare it in its throws clause.

42. What is the difference between a MenuItem and a CheckboxMenuItem?
The CheckboxMenuItem class extends the MenuItem class to support a menu item that may be checked or unchecked.
43. What is a task's priority and how is it used in scheduling?
A task's priority is an integer value that identifies the relative order in which it should be executed with respect to other tasks. The scheduler attempts to schedule higher priority tasks before lower priority tasks.

44. What class is the top of the AWT event hierarchy?
The java.awt.AWTEvent class is the highest-level class in the AWT event-class hierarchy.

45. When a thread is created and started, what is its initial state?
A thread is in the ready state after it has been created and started.

46. Can an anonymous class be declared as implementing an interface and extending a class?
An anonymous class may implement an interface or extend a superclass, but may not be declared to do both.

47. What is the range of the short type?
The range of the short type is -(2^15) to 2^15 - 1.

48. What is the range of the char type?
The range of the char type is 0 to 2^16 - 1.

49. In which package are most of the AWT events that support the event-delegation model defined?
Most of the AWT-related events of the event-delegation model are defined in the java.awt.event package. The AWTEvent class is defined in the java.awt package.
50. What is the immediate superclass of Menu?
MenuItem

51. What is the purpose of finalization?
The purpose of finalization is to give an unreachable object the opportunity to perform any cleanup processing before the object is garbage collected.

52. Which class is the immediate superclass of the MenuComponent class.
Object

53. What invokes a thread's run() method?
After a thread is started, via its start() method or that of the Thread class, the JVM invokes the thread's run() method when the thread is initially executed.

54. What is the difference between the Boolean & operator and the && operator?
If an expression involving the Boolean & operator is evaluated, both operands are evaluated. Then the & operator is applied to the operand. When an expression involving the && operator is evaluated, the first operand is evaluated. If the first operand returns a value of true then the second operand is evaluated. The && operator is then applied to the first and second operands. If the first operand evaluates to false, the evaluation of the second operand is skipped.

55. Name three subclasses of the Component class.
Box.Filler, Button, Canvas, Checkbox, Choice, Container, Label, List, Scrollbar, or TextComponent

56. What is the GregorianCalendar class?
The GregorianCalendar provides support for traditional Western calendars.
57. Which Container method is used to cause a container to be laid out and redisplayed?
validate()

58. What is the purpose of the Runtime class?
The purpose of the Runtime class is to provide access to the Java runtime system.

59. How many times may an object's finalize() method be invoked by the
garbage collector?
An object's finalize() method may only be invoked once by the garbage collector.

60. What is the purpose of the finally clause of a try-catch-finally statement?
The finally clause is used to provide the capability to execute code no matter whether or not an exception is thrown or caught.

61. What is the argument type of a program's main() method?
A program's main() method takes an argument of the String[] type.

62. Which Java operator is right associative?
The = operator is right associative.

63. What is the Locale class?
The Locale class is used to tailor program output to the conventions of a particular geographic, political, or cultural region.64. Can a double value be cast to a byte?
Yes, a double value can be cast to a byte.

65. What is the difference between a break statement and a continue statement?
A break statement results in the termination of the statement to which it applies (switch, for, do, or while). A continue statement is used to end the current loop iteration and return control to the loop statement.

66. What must a class do to implement an interface?
It must provide all of the methods in the interface and identify the interface in its implements clause.

67. What method is invoked to cause an object to begin executing as a separate thread?
The start() method of the Thread class is invoked to cause an object to begin executing as a separate thread.

68. Name two subclasses of the TextComponent class.
TextField and TextArea

69. What is the advantage of the event-delegation model over the earlier event-inheritance model?
The event-delegation model has two advantages over the event-inheritance model. First, it enables event handling to be handled by objects other than the ones that generate the events (or their containers). This allows a clean separation between a component's design and its use. The other advantage of the event-delegation model is that it performs much better in applications where many events are generated. This performance improvement is due to the fact that the event-delegation model does not have to repeatedly process unhandled events, as is the case of the event-inheritance
model.

70. Which containers may have a MenuBar?
Frame
71. How are commas used in the initialization and iteration parts of a for statement?
Commas are used to separate multiple statements within the initialization and iteration parts of a for statement.

72. What is the purpose of the wait(), notify(), and notifyAll() methods?
The wait(),notify(), and notifyAll() methods are used to provide an efficient way for threads to wait for a shared resource. When a thread executes an object's wait() method, it enters the waiting state. It only enters the ready state after another thread invokes the object's notify() or notifyAll() methods.

73. What is an abstract method?
An abstract method is a method whose implementation is deferred to a subclass.

74. How are Java source code files named?
A Java source code file takes the name of a public class or interface that is defined within the file. A source code file may contain at most one public class or interface. If a public class or interface is defined within a source code file, then the source code file must take the name of the public class or interface. If no public class or interface is defined within a source code file, then the file must take on a name that is different than its classes and interfaces. Source code files use the .java extension.

75. What is the relationship between the Canvas class and the Graphics class?
A Canvas object provides access to a Graphics object via its paint() method.

76. What are the high-level thread states?
The high-level thread states are ready, running, waiting, and dead.

77. What value does read() return when it has reached the end of a file?
The read() method returns -1 when it has reached the end of a file.
78. Can a Byte object be cast to a double value?
No, an object cannot be cast to a primitive value.

79. What is the difference between a static and a non-static inner class?
A non-static inner class may have object instances that are associated with instances of the class's outer class. A static inner class does not have any object instances.

80. What is the difference between the String and StringBuffer classes?
String objects are constants. StringBuffer objects are not.

81. If a variable is declared as private, where may the variable be accessed?
A private variable may only be accessed within the class in which it is declared.

82. What is an object's lock and which objects have locks?
An object's lock is a mechanism that is used by multiple threads to obtain synchronized access to the object. A thread may execute a synchronized method of an object only after it has acquired the object's lock. All objects and classes have locks. A class's lock is acquired on the class's Class object.

83. What is the Dictionary class?
The Dictionary class provides the capability to store key-value pairs.

84. How are the elements of a BorderLayout organized?
The elements of a BorderLayout are organized at the borders (North, South, East, and West) and the center of a container.
85. What is the % operator?
It is referred to as the modulo or remainder operator. It returns the remainder of dividing the first operand by the second operand.

86. When can an object reference be cast to an interface reference?
An object reference be cast to an interface reference when the object implements the referenced interface.

87. What is the difference between a Window and a Frame?
The Frame class extends Window to define a main application window that can have a menu bar.

88. Which class is extended by all other classes?
The Object class is extended by all other classes.

89. Can an object be garbage collected while it is still reachable?
A reachable object cannot be garbage collected. Only unreachable objects may be garbage collected..

90. Is the ternary operator written x : y ? z or x ? y : z ?
It is written x ? y : z.

91. What is the difference between the Font and FontMetrics classes?
The FontMetrics class is used to define implementation-specific properties, such as ascent and descent, of a Font object.
92. How is rounding performed under integer division?
The fractional part of the result is truncated. This is known as rounding toward zero.

93. What happens when a thread cannot acquire a lock on an object?
If a thread attempts to execute a synchronized method or synchronized statement and is unable to acquire an object's lock, it enters the waiting state until the lock becomes available.

94. What is the difference between the Reader/Writer class hierarchy and the InputStream/OutputStream class hierarchy?
The Reader/Writer class hierarchy is character-oriented, and the InputStream/OutputStream class hierarchy is byte-oriented.

95. What classes of exceptions may be caught by a catch clause?
A catch clause can catch any exception that may be assigned to the Throwable type. This includes the Error and Exception types.

96. If a class is declared without any access modifiers, where may the class be accessed?
A class that is declared without any access modifiers is said to have package access. This means that the class can only be accessed by other classes and interfaces that are defined within the same package.

97. What is the SimpleTimeZone class?
The SimpleTimeZone class provides support for a Gregorian calendar.

98. What is the Map interface?
The Map interface replaces the JDK 1.1 Dictionary class and is used associate keys with values.99. Does a class inherit the constructors of its superclass?
A class does not inherit constructors from any of its super classes.

100. For which statements does it make sense to use a label?
The only statements for which it makes sense to use a label are those statements that can enclose a break or continue statement.

101. What is the purpose of the System class?
The purpose of the System class is to provide access to system resources.

102. Which TextComponent method is used to set a TextComponent to the read-only state?
setEditable()

103. How are the elements of a CardLayout organized?
The elements of a CardLayout are stacked, one on top of the other, like a deck of cards.

104. Is &amp;amp;amp;amp;amp;&= a valid Java operator?
No, it is not.

105. Name the eight primitive Java types.
The eight primitive types are byte, char, short, int, long, float, double, and boolean.
106. Which class should you use to obtain design information about an object?
The Class class is used to obtain information about an object's design.

107. What is the relationship between clipping and repainting?
When a window is repainted by the AWT painting thread, it sets the clipping regions to the area of the window that requires repainting.

108. Is "abc" a primitive value?
The String literal "abc" is not a primitive value. It is a String object.

109. What is the relationship between an event-listener interface and an event-adapter class?
An event-listener interface defines the methods that must be implemented by an event handler for a particular kind of event. An event adapter provides a default implementation of an event-listener interface.

110. What restrictions are placed on the values of each case of a switch statement?
During compilation, the values of each case of a switch statement must evaluate to a value that can be promoted to an int value.

111. What modifiers may be used with an interface declaration?
An interface may be declared as public or abstract.

112. Is a class a subclass of itself?
A class is a subclass of itself.
113. What is the highest-level event class of the event-delegation model?
The java.util.EventObject class is the highest-level class in the event-delegation class hierarchy.

114. What event results from the clicking of a button?
The ActionEvent event is generated as the result of the clicking of a button.

115. How can a GUI component handle its own events?
A component can handle its own events by implementing the required event-listener interface and adding itself as its own event listener.

116. What is the difference between a while statement and a do statement?
A while statement checks at the beginning of a loop to see whether the next loop iteration should occur. A do statement checks at the end of a loop to see whether the next iteration of a loop should occur. The do statement will always execute the body of a loop at least once.

117. How are the elements of a GridBagLayout organized?
The elements of a GridBagLayout are organized according to a grid. However, the elements are of different sizes and may occupy more than one row or column of the grid. In addition, the rows and columns may have different sizes.

118. What advantage do Java's layout managers provide over traditional windowing systems?
Java uses layout managers to lay out components in a consistent manner across all windowing platforms. Since Java's layout managers aren't tied to absolute sizing and positioning, they are able to accommodate platform-specific differences among windowing systems.

119. What is the Collection interface?
The Collection interface provides support for the implementation of a mathematical bag - an unordered collection of objects that may contain duplicates.
120. What modifiers can be used with a local inner class?
A local inner class may be final or abstract.

121. What is the difference between static and non-static variables?
A static variable is associated with the class as a whole rather than with specific instances of a class. Non-static variables take on unique values with each object instance.

122. What is the difference between the paint() and repaint() methods?
The paint() method supports painting via a Graphics object. The repaint() method is used to cause paint() to be invoked by the AWT painting thread.

123. What is the purpose of the File class?
The File class is used to create objects that provide access to the files and directories of a local file system.

124. Can an exception be rethrown?
Yes, an exception can be rethrown.

125. Which Math method is used to calculate the absolute value of a number?
The abs() method is used to calculate absolute values.

126. How does multithreading take place on a computer with a single CPU?
The operating system's task scheduler allocates execution time to multiple tasks. By quickly switching between executing tasks, it creates the impression that tasks execute sequentially.
127. When does the compiler supply a default constructor for a class?
The compiler supplies a default constructor for a class if no other constructors are provided.

128. When is the finally clause of a try-catch-finally statement executed?
The finally clause of the try-catch-finally statement is always executed unless the thread of execution terminates or an exception occurs within the execution of the finally clause.

129. Which class is the immediate superclass of the Container class?
Component

130. If a method is declared as protected, where may the method be accessed?
A protected method may only be accessed by classes or interfaces of the same package or by subclasses of the class in which it is declared.

131. How can the Checkbox class be used to create a radio button?
By associating Checkbox objects with a CheckboxGroup.

132. Which non-Unicode letter characters may be used as the first character of an identifier?
The non-Unicode letter characters $ and _ may appear as the first character of an identifier

133. What restrictions are placed on method overloading?
Two methods may not have the same name and argument list but different return types.
134. What happens when you invoke a thread's interrupt method while it is sleeping or waiting?
When a task's interrupt() method is executed, the task enters the ready state. The next time the task enters the running state, an InterruptedException is thrown.

135. What is casting?
There are two types of casting, casting between primitive numeric types and casting between object references. Casting between numeric types is used to convert larger values, such as double values, to smaller values, such as byte values. Casting between object references is used to refer to an object by a compatible class, interface, or array type reference.

136. What is the return type of a program's main() method?
A program's main() method has a void return type.

137. Name four Container classes.
Window, Frame, Dialog, FileDialog, Panel, Applet, or ScrollPane

138. What is the difference between a Choice and a List?
A Choice is displayed in a compact form that requires you to pull it down to see the list of available choices. Only one item may be selected from a Choice. A List may be displayed in such a way that several List items are visible. A List supports the selection of one or more List items.

139. What class of exceptions are generated by the Java run-time system?
The Java runtime system generates RuntimeException and Error exceptions.

140. What class allows you to read objects directly from a stream?
The ObjectInputStream class supports the reading of objects from input streams.
141. What is the difference between a field variable and a local variable?
A field variable is a variable that is declared as a member of a class. A local variable is a variable that is declared local to a method.

142. Under what conditions is an object's finalize() method invoked by the garbage collector?
The garbage collector invokes an object's finalize() method when it detects that the object has become unreachable.

143. How are this () and super () used with constructors?
this() is used to invoke a constructor of the same class. super() is used to invoke a superclass constructor.

144. What is the relationship between a method's throws clause and the exceptions that can be thrown during the method's execution?
A method's throws clause must declare any checked exceptions that are not caught within the body of the method.

145. What is the difference between the JDK 1.02 event model and the event-delegation model introduced with JDK 1.1?
The JDK 1.02 event model uses an event inheritance or bubbling approach. In this model, components are required to handle their own events. If they do not handle a particular event, the event is inherited by (or bubbled up to) the component's container. The container then either handles the event or it is bubbled up to its container and so on, until the highest-level container has been tried.
In the event-delegation model, specific objects are designated as event handlers for GUI components. These objects implement event-listener interfaces. The event-delegation model is more efficient than the event-inheritance model because it eliminates the processing required to support the bubbling of unhandled events.

146. How is it possible for two String objects with identical values not to be equal under the == operator?
The == operator compares two objects to determine if they are the same object in memory. It is possible for two String objects to have the same value, but located indifferent areas of memory.

147. Why are the methods of the Math class static?
So they can be invoked as if they are a mathematical code library.
148. What Checkbox method allows you to tell if a Checkbox is checked?
getState()

149. What state is a thread in when it is executing?
An executing thread is in the running state.

150. What are the legal operands of the instanceof operator?
The left operand is an object reference or null value and the right operand is a class, interface, or array type.

151. How are the elements of a GridLayout organized?
The elements of a GridBad layout are of equal size and are laid out using the squares of a grid.

152. What an I/O filter?
An I/O filter is an object that reads from one stream and writes to another, usually altering the data in some way as it is passed from one stream to another.

153. If an object is garbage collected, can it become reachable again?
Once an object is garbage collected, it ceases to exist. It can no longer become reachable again.

154. What is the Set interface?
The Set interface provides methods for accessing the elements of a finite mathematical set. Sets do not allow duplicate elements.
155. What classes of exceptions may be thrown by a throw statement?
A throw statement may throw any expression that may be assigned to the Throwable type.

156. What are E and PI?
E is the base of the natural logarithm and PI is mathematical value pi.

157. Are true and false keywords?
The values true and false are not keywords.

158. What is a void return type?
A void return type indicates that a method does not return a value.

159. What is the purpose of the enableEvents() method?
The enableEvents() method is used to enable an event for a particular object. Normally, an event is enabled when a listener is added to an object for a particular event. The enableEvents() method is used by objects that handle events by overriding their event-dispatch methods.

160. What is the difference between the File and RandomAccessFile classes?
The File class encapsulates the files and directories of the local file system. The RandomAccessFile class provides the methods needed to directly access data contained in any part of a file.

161. What happens when you add a double value to a String?
The result is a String object.162. What is your platform's default character encoding?
If you are running Java on English Windows platforms, it is probably Cp1252. If you are running Java on English Solaris platforms, it is most likely 8859_1..

163. Which package is always imported by default?
The java.lang package is always imported by default.

164. What interface must an object implement before it can be written to a stream as an object?
An object must implement the Serializable or Externalizable interface before it can be written to a stream as an object.

165. How are this and super used?
this is used to refer to the current object instance. super is used to refer to the variables and methods of the superclass of the current object instance.

166. What is the purpose of garbage collection?
The purpose of garbage collection is to identify and discard objects that are no longer needed by a program so that their resources may be reclaimed and
reused.

167. What is a compilation unit?
A compilation unit is a Java source code file.

168. What interface is extended by AWT event listeners?
All AWT event listeners extend the java.util.EventListener interface.
169. What restrictions are placed on method overriding?
Overridden methods must have the same name, argument list, and return type.
The overriding method may not limit the access of the method it overrides.
The overriding method may not throw any exceptions that may not be thrown
by the overridden method.

170. How can a dead thread be restarted?
A dead thread cannot be restarted.

171. What happens if an exception is not caught?
An uncaught exception results in the uncaughtException() method of the thread's ThreadGroup being invoked, which eventually results in the termination of the program in which it is thrown.

172. What is a layout manager?
A layout manager is an object that is used to organize components in a container.

173. Which arithmetic operations can result in the throwing of an ArithmeticException?
Integer / and % can result in the throwing of an ArithmeticException.

174. What are three ways in which a thread can enter the waiting state?
A thread can enter the waiting state by invoking its sleep() method, by blocking on I/O, by unsuccessfully attempting to acquire an object's lock, or by invoking an object's wait() method. It can also enter the waiting state by invoking its
(deprecated) suspend() method.

175. Can an abstract class be final?
An abstract class may not be declared as final.176. What is the ResourceBundle class?
The ResourceBundle class is used to store locale-specific resources that can be loaded by a program to tailor the program's appearance to the particular locale in which it is being run.

177. What happens if a try-catch-finally statement does not have a catch clause to handle an exception that is thrown within the body of the try statement?
The exception propagates up to the next higher level try-catch statement (if any) or results in the program's termination.

178. What is numeric promotion?
Numeric promotion is the conversion of a smaller numeric type to a larger numeric type, so that integer and floating-point operations may take place. In numerical promotion, byte, char, and short values are converted to int
values. The int values are also converted to long values, if necessary. The long and float values are converted to double values, as required.

179. What is the difference between a Scrollbar and a ScrollPane?
A Scrollbar is a Component, but not a Container. A ScrollPane is a Container. A ScrollPane handles its own events and performs its own scrolling.

180. What is the difference between a public and a non-public class?
A public class may be accessed outside of its package. A non-public class may not be accessed outside of its package.

181. To what value is a variable of the boolean type automatically initialized?
The default value of the boolean type is false.

182. Can try statements be nested?
Try statements may be tested.
183. What is the difference between the prefix and postfix forms of the ++ operator?
The prefix form performs the increment operation and returns the value of the increment operation. The postfix form returns the current value all of the expression and then performs the increment operation on that value.

184. What is the purpose of a statement block?
A statement block is used to organize a sequence of statements as a single statement group.

185. What is a Java package and how is it used?
A Java package is a naming context for classes and interfaces. A package is used to create a separate name space for groups of classes and interfaces. Packages are also used to organize related classes and interfaces into a single API unit and to control accessibility to these classes and interfaces.

186. What modifiers may be used with a top-level class?
A top-level class may be public, abstract, or final.

187. What are the Object and Class classes used for?
The Object class is the highest-level class in the Java class hierarchy. The Class class is used to represent the classes and interfaces that are loaded by a Java program.

188. How does a try statement determine which catch clause should be used to handle an exception?
When an exception is thrown within the body of a try statement, the catch clauses of the try statement are examined in the order in which they appear. The first catch clause that is capable of handling the exception is executed.
The remaining catch clauses are ignored.

189. Can an unreachable object become reachable again?
An unreachable object may become reachable again. This can happen when the object's finalize() method is invoked and the object performs an operation which causes it to become accessible to reachable objects.190. When is an object subject to garbage collection?
An object is subject to garbage collection when it becomes unreachable to the program in which it is used.

191. What method must be implemented by all threads?
All tasks must implement the run() method, whether they are a subclass of Thread or implement the Runnable interface.

192. What methods are used to get and set the text label displayed by a Button object?
getLabel() and setLabel()

193. Which Component subclass is used for drawing and painting?
Canvas

194. What are synchronized methods and synchronized statements?
Synchronized methods are methods that are used to control access to an object. A thread only executes a synchronized method after it has acquired the lock for the method's object or class. Synchronized statements are similar to synchronized methods. A synchronized statement can only be executed after a thread has acquired the lock for the object or class referenced in the synchronized statement195. What are the two basic ways in which classes that can be run as threads may be defined?
A thread class may be declared as a subclass of Thread, or it may implement the Runnable interface.

196. What are the problems faced by Java programmers who don't use layout managers?
Without layout managers, Java programmers are faced with determining how their GUI will be displayed across multiple windowing systems and finding a common sizing and positioning that will work within the constraints imposed by each windowing system.

197. What is the difference between an if statement and a switch statement?
The if statement is used to select among two alternatives. It uses a boolean expression to decide which alternative should be executed. The switch statement is used to select among multiple alternatives. It uses an int expression to determine which alternative should be executed.

Q 1- What do we call an operator that operates on only one operand? A - An operator that operates on only one operand is called a unary operator.
Q 2- What do we call an operator that operates on two operands? A - An operator that operates on two operands is called a binary operator.
Q 3- Is the minus sign a unary or a binary operator, or both? Explain your answer. A - Both. As a binary operator, the minus sign causes its right operand to be subtracted from its left operand. As a unary operator, the minus sign causes the algebraic sign of the right operand to be changed.
Q 4- Describe operator overloading. A - For those languages that support it (such as C++) operator overloading means that the programmer canredefine the behavior of an operator with respect to objects of a new type defined by that program.
Q5- Java programmers may overload operators: True or False? A 6- False: Unfortunately, Java does not support operator overloading.
Q7 - Show the symbols used for the following operators in Java: assignment, not equal, addition,cast. A - The above listed operators in order are: = != + (type)
Q8 - Is any operator automatically overloaded in Java? If so, identify it and describe its overloadedbehavior. A - The plus sign (+) is automatically overloaded in Java. The plus sign can be used to perform arithmeticaddition. It can also be used to concatenate strings. However, the plus sign does more than concatenate strings. It also performs a conversion to String type. When the plus sign is used to concatenate strings, the operand on the right is automatically converted to a character string before being concatenated with the operand on the left. This assumes that the compiler knows enough about the operand on the right to be able to successfully perform the conversion. It has that knowledge for all of the primitive types and most or all of the built-in reference types.
Q 9- What is the purpose of the cast operator? A - The cast operator is used to purposely convert from one type to another.
Q10 - The increment operator is a binary operator: True or False? A - False: The increment operator is a unary operator.
Q11 - Show the symbol for the increment operator. A - The symbol for the increment operator is two plus signs with nothing between them (++).

Q 12- Describe the appearance and the behavior of the increment operator with both prefix andpostfix notation. Show example, possibly incomplete, code fragments illustrating both notationalforms.
A - The increment operator may be used with both prefix and postfix notation. Basically, the increment operator causes the value of the variable to which it is applied to be increased by one. With prefix notation, the operand appears to the right of the operator ( ++X), while with postfix notation, the operand appears to the left of the operator (X++). The difference in behavior has to do with the point in time that the increment actually occurs if the operator and its operand appear as part of a larger overall expression. With the prefix version, the variable is incremented before it is used to evaluate the larger overall expression. With the postfix version, the variable is used to evaluate the larger overall expression and then it is incremented.
Q13 - Show the output that would be produced by the following Java application.

class prg1
{ //define the controlling class
public static void main(String[] args)
{ //define main methodint x = 5, X = 5, y = 5, Y = 5;
System.out.println("x = " + x );
System.out.println("X = " + X );
System.out.println("x + X++ = " + (x + X++) );
System.out.println("X = " + X );
System.out.println();
System.out.println("y = " + y );
System.out.println("Y = " + Y );
System.out.println("y + ++Y = " + (y + ++Y) );
System.out.println("Y = " + Y );
}
//end main}//End class.

Note no semicolon required//End Java applicationA -

The output from this Java application follows:x = 5X = 5x + X++ = 10X = 6y = 5Y = 5y + ++Y = 11Y = 6

Q 14 - Binary operators use outfix notation: True or False? If your answer is False, explain why.
A - False: Binary operators use infix notation, which means that the operator appears between its operands.
Q15 - In practice, what does it mean to say that an operator that has performed an action returns avalue (or evaluates to a value) of a given type? A - As a result of performing the specified action, an operator can be said to return a value (or evaluate to avalue) of a given type. The type depends on the operator and the type of the operands. To evaluate to a value means that after the action is performed, the operator and its operands are effectively replaced in the expression by the value that is returned.
Q 16 - What are the four categories of operators described in Baldwin's Java tutorial on operators? Doyou agree with this categorization? If not, explain why not. A - Some authors divide Java's operators into the following categories:arithmetic relational and conditional (typically called relational and logical in C++) bitwise and logical assignment
Q17 - Show and describe at least five of the binary arithmetic operators supported by Java(Clarification: binary operators does not mean bitwise operators). A - Java support various arithmetic operators on floating point and integer numbers. The following table lists five of the binary arithmetic operators supported by Java. Operator Description + Adds its operands - Subtracts the right operand from the left operand* Multiplies the operands / Divides the left operand by the right operand % Remainder of dividing the left operand by the right operand
Q18 - In addition to arithmetic addition, what is another use for the plus operator (+)? Show anexample code fragment to illustrate your answer. The code fragment need not be a completestatement. A - The plus operator (+) is also used to concatenate strings : "IMR " + " global Ltd."
Q19 - When the plus operator (+) is used as a concatenation operator, what is the nature of itsbehavior if its right operand is not of type String? If the right operand is a variable that is not of typeString, what is the impact of this behavior on that variable. A - In this case, the operator also coerces the value of the right operand to a string representation for use in the expression only. If the right operand is a variable, the value stored in the variable is not modified in any way.
Q 20- Show and describe four unary arithmetic operators supported by Java. A - Java supports the following four unary arithmetic operators. Operator Description + Indicates a positive value - Negates, or changes algebraic sign ++ Adds one to the operand, both prefix and postfix-- Subtracts one from operand, prefix and postfix
Q20 - What is the type returned by relational operators in Java? A - Relational operators return the boolean type in Java.
Q 21- Show and describe six different relational operators supported by Java. A - Java supports the following set of relational operators: Operator Returns true if > Left operand is greater than right operand >= Left operand is greater than or equal to right operand< operand="=">5 is " + (6>5 ) );}//end main}//End class. Note no semicolon required//End Java applicationA - This program produces the following output: The relational 6<5>5 is true
Q23 - Show and describe three operators (frequently referred to as conditional operators in Java andlogical operators in C++) which are often combined with relational operators to construct morecomplex expressions (often called conditional expressions). Hint: The && operator returns true ifthe left and right operands are both true. What are the other two and how do they behave? A - The following three logical or conditional operators are supported by Java. Operator Typical Use Returns true if &&amp;amp;amp; Left && Right Left and Right are both true Left Right Either Left or Right is true ! ! Right Right is false
Q24 - Describe the special behavior of the operator in the following expression for the case wherethe value of the variable a is less than the value of the variable b. (a <>> OpLeft >> Dist Shift bits of OpLeft right by Dist bits (signed)<<>>> OpLeft >>> Dist Shift bits of OpLeft right by Dist bits (unsigned)& OpLeft & OpRight Bitwise and of the two operands OpLeft OpRight Bitwise inclusive or of the two operands ^ OpLeft ^ OpRight Bitwise exclusive or (xor) of the two operands~ ~ OpRight Bitwise complement of the right operand (unary)
Q28 - In Java, the signed right shift operation populates the vacated bits with the zeros, while the leftshift and the unsigned right shift populate the vacated bits with the sign bit: True or False. If youranswer is False, explain why. A - False: In Java, the signed right shift operation populates the vacated bits with the sign bit, while the left shift and the unsigned right shift populate the vacated bits with zeros.
Q29 - In a signed right-shift operation in Java, the bits shifted off the right end are lost: True or False.If your answer is False, explain why. A - True: For both Java and C++, bits shifted off the right end are lost.
Q30 - Using the symbols 1 and 0 construct a table showing the four possible combinations of 1 and 0.Using a 1 or a 0, show the result of the bitwise and operation on these four combinations of 1 and 0. A - The answer is: 1 and 1 produces 11 and 0 produces 00 and 1 produces 00 and 0 produces 0
Q 31- Using the symbols 1 and 0 construct a truth table showing the four possible combinations of 1and 0. Using a 1 or a 0, show the result of the bitwise inclusive or operation on these fourcombinations on these four combinations of 1 and 0. A - The answer for the inclusive or is: 1 or 1 produces 11 or 0 produces 10 or 1 produces 10 or 0 produces 0
Q 32- Using the symbols 1 and 0 construct a truth table showing the four possible combinations of 1and 0. Using a 1 or a 0, show the result of the bitwise exclusive or operation on these fourcombinations on these four combinations of 1 and 0. A - The answer for the exclusive or is: 1 xor 1 produces 01 xor 0 produces 10 xor 1 produces 10 xor 0 produces 0
Q 33- For the exclusive or, if the two bits are different, the result is a 1. If the two bits are the same,the result is a 0. True or False? If your answer is False, explain why. A - True.
Q 34- Is the assignment operator a unary operator or a binary operator. Select one or the other. A - The assignment operator is a binary operator.
Q 35- In Java, when using the assignment operator, the value stored in memory and represented by theright operand is copied into the memory represented by the left operand: True or False? If youranswer is False, explain why. A - True.
Q 36- Show two of the shortcut assignment operators and explain how they behave by comparingthem with the regular (nonshortcut) versions. Hint: The (^=) operator is a shortcut assignmentoperator. A - Java supports the following list of shortcut assignment operators. These operators allow you to perform an assignment and another operation with a single operator. += -= *= /= %= &= = ^= <<= >>= >>>=For example, the two statements which follow perform the same operation.x += y; x = x + y;The behavior of all the shortcut assignment operators follows this same pattern.
Q 37 - Write a Java application illustrates the difference between the prefix and the postfix versions of the increment operator.
class prog3{static public void main(String[] args){int x = 3;int y = 3;int z = 10;System.out.println("Prefix version gives " + (z + ++x));System.out.println("Postfix version gives " + (z + y++));}//end main}//end class
Q38 Write a Java application that illustrates the use of the following relational operators: < > <= >= == !=class Prog4 { //define the controlling classpublic static void main(String[] args){ //define main methodSystem.out.println("The relational 6<5>5 is " + (6>5 ) );System.out.println("The relational 5>=5 is " + (5>=5 ) );System.out.println("The relational 5<=5 is " + (5<=5 ) );System.out.println("The relational 6==5 is " + (6==5 ) );System.out.println("The relational 6!=5 is " + (6!=5 ) );}//end main}//End prog4 class. Note no semicolon required Q39 - Write a Java application that illustrates the use of the following logical or conditional operators:&& ! class prg5 { //define the controlling classpublic static void main(String[] args){ //define main methodSystem.out.println("true and true is " + (true &&amp;amp;amp; true) );System.out.println("true and false is " + (true && false) ); System.out.println("true or true is " + (true true) );System.out.println("true or false is " + (true false) );System.out.println("false or false is " + (false false) );System.out.println("not true is " + (! true) );System.out.println("not false is " + (! false) ); }//end main} Q40 - Java supports a constant type: True or False. If false, explain why. A - Java does not support a constant type. However, in Java, it is possible to achieve the same result bydeclaring and initializing a variable and making it final. Q41 Provide a code fragment that illustrates the syntax for creating a named constant in Java. A - The syntax for creating a named constant in Java is as follows: final float PI = 3.14159; Q42 - What is the common method of controlling the order of evaluation of expressions in Java? A - you can control the order of evaluation by the use of parentheses. Q43 - What are the three actions normally involved in the operation of a loop (in addition to executingthe code in the body of the loop)? A - The operation of a loop normally involves the following three actions in addition to executing the code in the body of the loop:Initialize a control variable. Test the control variable in a conditional expression. Update the control variable. Q - Java provides two different string classes from which string objects can be instantiated. Whatare they?
A - The two classes are:
String StringBuffer
Q - The StringBuffer class is used for strings that are not allowed to change. The String class isused for strings that are modified by the program: True or False. If false, explain why.
A - False. This statement is backwards. The String class is used for strings that are not allowed to change. TheStringBuffer class is used for strings that are modified by the program.
Q - While the contents of a String object cannot be modified, a reference to a String object can becaused to point to a different String object: True or False. If false, explain why.
A - True.
Q - The use of the new operator is required for instantiation of objects of type String: True orFalse? If false, explain your answer.
A - False. A String object can be instantiated using either of the following statements:
String str1 = new String("String named str2");

String str2 = "String named str1";

Q - The use of the new operator is required for instantiation of objects of type StringBuffer: Trueor False? If false, explain your answer.
A - True.
Q - Provide a code fragment that illustrates how to instantiate an empty StringBuffer object of adefault length and then use a version of the append() method to put some data into the object.
A - See code fragment below:
StringBuffer str5 = new StringBuffer();//accept default initial length
str5.append("StringBuffer named str5");//modify length as needed

Q - Without specifying any explicit numeric values, provide a code fragment that will instantiate anempty StringBuffer object of the correct initial length to contain the string "StringBuffer named str6"and then store that string in the object.
A - See the following code fragment:
StringBuffer str6 = new StringBuffer("StringBuffer named str6".length());
str6.append("StringBuffer named str6");

Q - Provide a code fragment consisting of a single statement showing how to use the Integerwrapper class to convert a string containing digits to an integer and store it in a variable of type int.
A - See code fragment below
int num = new Integer("3625").intValue();

Q - Explain the difference between the capacity() method and the length() methods of theStringBuffer class.
A - The capacity() method returns the amount of space currently allocated for the StringBuffer object. Thelength() method returns the amount of space used.
Q - The following is a valid code fragment: True or False? If false, explain why.
StringBuffer str6 = new StringBuffer("StringBuffer named str6".length());A - True.
Q - Which of the following code fragments is the most efficient, first or second?
String str1 = "THIS STRING IS NAMED str1";String str1 = new String("THIS STRING IS NAMED str1");
A - The first code fragment is the most efficient.
System
Java provides the System class which provides a platform-dependent interface between yourprogram and various system resources: True or False? If false, explain why.
A - False. Java provides the System class which provides a platform-independent interface between yourprogram and those resources.
Q - You must instantiate an object of the System class in order to use it: True or False? If false,explain why.
A - False. You don't need to instantiate an object of the System class to use it, because all of its variables andmethods are class variables and methods.
Q - The following code fragment can be used to instantiate an object of the System class: True orFalse? If false, explain why.
System mySystemObject = new System();

A - False. You cannot instantiate an object of the System class. It is a final class, and all of its constructors areprivate.
Q - What is the purpose of the write() method of the PrintStream class?
A - The write() method is used to write bytes to the stream. You can use write() to write data which is notintended to be interpreted as text (such as bit-mapped graphics data).
Exceptions
Q - The exception-handling capability of Java makes it possible for you to monitor for exceptionalconditions within your program, and to transfer control to special exception-handling code which youdesign. List five keywords that are used for this purpose.
A - try, throw, catch, finally, and throws
Q - All exceptions in Java are thrown by code that you write: True or False? If false, explain why.
A - False. There are situations where an exceptional condition automatically transfers control to specialexception-handling code which you write (cases where you don't provide the code to throw the exception object).
Q - When an exceptional condition causes an exception to be thrown, that exception is an objectderived, either directly, or indirectly from the class Exception: True or False? If false, explain why.
A - False. When an exceptional condition causes an exception to be thrown, that exception is an object derived,either directly, or indirectly from the class Throwable.
Q - All exceptions other than those in the RuntimeException class must be either caught, ordeclared in a throws clause of any method that can throw them: True or False? If false, explainwhy.
A - True.
Q - What method of which class would you use to extract the message from an exception object?
A - The getMessage() method of the Throwable class.
Q - Normally, those exception handlers designed to handle exceptions closest to the root of theexception class hierarchy should be placed first in the list of exception handlers: True or False? Iffalse, explain why.
A - False. The above statement has it backwards. Those handlers designed to handle exceptions furthermost fromthe root of the hierarchy tree should be placed first in the list of exception handlers.
Q - Explain why you should place exception handlers furthermost from the root of the exceptionhierarchy tree first in the list of exception handlers.
A - An exception hander designed to handle a specialized "leaf" object may be preempted by another handlerwhose exception object type is closer to the root of the exception hierarchy tree if the second exception handlerappears earlier in the list of exception handlers.
Q - In addition to writing handlers for very specialized exception objects, the Java language allowsyou to write general exception handlers that handle multiple types of exceptions: True or False? Iffalse, explain why.
A - True.
Q - Your exception handler can be written to handle any class that inherits from Throwable. If youwrite a handler for a node class (a class with no subclasses), you've written a specialized handler: itwill only handle exceptions of that specific type. If you write a handler for a leaf class (a class withsubclasses), you've written a general handler: it will handle any exception whose type is the nodeclass or any of its subclasses. True or False? If false, explain why.
A - False. "Leaf" and "node" are reversed in the above statement. If you write a handler for a "leaf" class (a classwith no subclasses), you've written a specialized handler: it will only handle exceptions of that specific type. Ifyou write a handler for a "node" class (a class with subclasses), you've written a general handler: it will handleany exception whose type is the node class or any of its subclasses."
Q - Java's finally block provides a mechanism that allows your method to clean up after itselfregardless of what happens within the try block. True or False? If false, explain why.
A - True.
Q - Explain how you would specify that a method throws one or more exceptions.
A - To specify that a method throws one or more exceptions, you add a throws clause to the method signature forthe method. The throws clause is composed of the throws keyword followed by a comma-separated list of all theexceptions thrown by that method.
Q - Provide a code fragment that illustrates how you would specify that a method throws more thanone exception.
A - See code fragment below.
void myMethod() throws InterruptedException, MyException,
HerException, UrException
{
//method body
}

Q - What type of argument is required by the throw statement?
A - The throw statement requires a single argument, which must be an object derived either directly or indirectlyfrom the class Throwable.
Q - Some exception objects are automatically thrown by the system. It is also possible for you todefine your own exception classes, and to cause objects of those classes to be thrown whenever anexception occurs. True or False? If false, explain why.
A - True.

=======
Threads
Q - What is the definition of multi-threaded programming according to Patrick Naughton?
A - According to The Java Handbook, by Patrick Naughton,
"Multi-threaded programming is a conceptual paradigm for programming where you divide programs into two or more processes which can be run in parallel."
Q - Multithreading refers to two or more programs executing, "apparently" concurrently, undercontrol of the operating system. The programs need have no relationship with each other, other thanthe fact that you want to start and run them all concurrently. True or False? If false, explain why.
A - False. That is a description of multiprocessing, not multithreading. Multithreading refers to two or moretasks executing, "apparently" concurrently, within a single program.
Q - According to current terminology, the term blocked means that the thread is waiting forsomething to happen and is not consuming computer resources. True or False? If false, explain why.
A - True.
Q - What are the two ways to create threaded programs in Java?
A - In Java, there are two ways to create threaded programs:
Implement the Runnable interface Extend the Thread class
Q - What two steps are required to spawn a thread in Java?
A - The two steps necessary to spawn a thread in Java are:
instantiate an object of type Thread and invoke its run() method.
Q - How do you start a thread actually running in Java?
A - Invoke the start() method on object of the Thread class or of a subclass of the Thread class.
Q - It is always possible to extend the Thread class in your Java applications and applets. True orFalse? If false, explain why.
A - False. Sometimes it is not possible to extend the Thread class, because you must extend some other class and Java does not support multiple inheritance.
Q - Although multithreaded programming in Java is possible, it is also possible to write Javaprograms that do not involve threads: True or False? If false, explain why.
A - False. The main method itself runs in a thread which is started by the interpreter.
Q - What is the name of the method that can be used to determine if a thread is alive?
A - The name of the method is isAlive().
Q - Once you start two or more threads running, unless you specify otherwise, they runsynchronously and independently of one another: True or False? If false, explain why.
A - False. Once you start two or more threads running, unless you specify otherwise, they run asynchronouslyand independently of one another.
Q - The process of keeping one thread from corrupting the data while it is being processed byanother thread is known as synchronization: True or False? If false, explain why.
A - True.
Q - Java allows you to specify the absolute priority of each thread: True or False? If false, explainwhy.
A - False. Java allows you to specify the priority of each thread relative to other threads but not on an absolute basis.
Q - Thread synchronization can be achieved using wait(), notify(), and notifyAll() which aremethods of the Thread class: True or False? If false, explain why.
A - False. wait(), notify(), and notifyAll() are not methods of the Thread class, but rather are methods of theObject class.
Q - When you implement a threaded program, you will always override the _____________method of the Thread class and build the functionality of your threaded program into that method.What is the name of the method?
A - The run() method.
Q - In a multithreaded program, you will start a thread running by invoking the __________ methodon your Thread object which will in turn invoke the ___________ method. What are the names ofthe missing methods, and what are the required parameters for each method?
A - In a multithreaded program, you will start a thread running by invoking the start() method on your Thread object which will in turn invoke the run() method. Neither method takes any parameters.
Q - What do Campione and Walrath list as the four possible states of a thread?
A - New Thread Runnable Not Runnable Dead
Q - What methods can be invoked on a thread object which is in the state that Campione andWalrath refer to as a New Thread and what will happen if you invoke any other method on thethread?
A - When a thread is in this state, you can only start the thread or stop it. Calling any method other than start()or stop() will cause an IllegalThreadStateException.
Q - What, according to Campione and Walrath, will cause a thread to become Not Runnable?
A - a thread becomes Not Runnable when one of the following four events occurs:
Someone invokes its sleep() method. Someone invokes its suspend() method. The thread uses its wait() method to wait on a condition variable. The thread is blocking on I/O.
Q1 - Three keywords are used in Java to specify access control. What are they? A - The three keywords used to specify access control in Java are public, private, and protected.
Q2 - In Java, special access privileges are afforded to other members of the same package: True orFalse? If false, explain your answer. A - True. In Java, special access privileges are afforded to other members of the same package.
Q3 - In Java, class variables are often used with the __________ keyword to create variables thatact like constants.
A - The final keyword.
Q4 - In Java, the ___________ keyword is used to declare a class variable.
A - The static keyword.
Q5 - In Java, the ___________ keyword is used to declare a class method.
A - The static keyword.
Q6 - When you include a method in a Java class definition without use of static keyword, this willresult in objects of that class containing an instance method: True or False? If false, explain why.
A 7- True.
Q8 - Normally each object contains its own copy of each instance method: True or False?
A - False, multiple copies of the method do not normally exist in memory.
Q9- When you invoke an instance method using a specific object, if that method refers to instancevariables of the class, that method is caused to refer to the specific instance variables of the specificobject for which it was invoked: True or False? If false, explain why.
A - True.
Q10 - Instance methods are invoked in Java using the name of the object, the colon, and the name ofthe method as shown below: True or False? If false, explain why.
myObject:myInstanceMethod( )
A - False. Use the period or dot operator, not the colon.
Q11 - Instance methods have access to both instance variables and class variables in Java: True orFalse. If false, explain why.
A - True.
Q12 - Class methods have access to both instance variables and class variables in Java: True orFalse. If false, explain why.
A - False. Class method can only access other class members.
Q13 - What are the two most significant characteristics of class methods?
A - 1. Class methods can only access other class members. 2. Class methods can be accessed using only thename of the class. An object of the class is not required to access class methods.
Q14 - In Java, a class method can be invoked using the name of the class, the colon, and the name ofthe method as shown below: True or False? If false, explain why.
MyClass:myClassMethod()
A - False. You must use the period or dot operator, not the colon.
Q15 - What is meant by overloaded methods?
A - The term overloaded methods means that two or more methods may have the same name so long as theyhave different argument lists.
Q16 - If you overload a method name, the compiler determines at run time, on the basis of thearguments provided to the invocation of the method, which version of the method to call in thatinstance: True or False? If false, explain why.
A - False. The determination is made at compile time.
Q16 - A constructor is a special method which is used to construct an object. A constructor alwayshas the same name as the class in which it is defined, and has no return type specified. True orFalse? If false, explain why.
A - True.
Q17 - Constructors may be overloaded, so a single class may have more than one constructor, all ofwhich have the same name, but different argument lists: True or False. If false, explain why.
A - True
Q18 - What is the purpose of a parameterized constructor?
A - The purpose of a parameterized constructor is to initialize the instance variables of an object when the object is instantiated.
Q 19 - The same set of instance variables can often be initialized in more than one way usingoverloaded constructors: True or False? If false, explain why.
A - True.
Q20 - It is not necessary to provide a constructor in Java. True or False? If false, explain why.
A - True. .
Q 21 You can think of the default constructor as a constructor which doesn't take any parameters:True or False? If false, explain why.
A - True.
Q 22- In Java, if you provide any constructors, the default constructor is no longer providedautomatically: True or False? If false, explain why.
A - True.
Q 23- In Java, if you need both a parameterized constructor and a constructor which doesn't takeparameters (often called a default constructor), you must provide them both: True or False? If false,explain why.
A - True.
Q 24- In Java, you can instantiate objects in static memory at compile time, or you can use the newoperator to request memory from the operating system at runtime and use the constructor toinstantiate the object in that memory: True or False? If false, explain why.
A - False. In Java, objects can only be instantiated on the heap at runtime.
Q25 - Provide a code fragment consisting of a single statement that illustrates how the constructor istypically used in Java to declare, instantiate, and initialize an object. Assume a parameterizedconstructor with three parameters of type int.
A - MyClass myObject = new MyClass(1,2,3);
Q26 - Provide a code fragment consisting of a single statement that illustrates how the defaultconstructor is typically used in Java to declare and instantiate an object.
A - MyClass myObject = new MyClass();
Q 27- What are the three actions performed by the following statement?
MyClass myObject = new MyClass(1,2,3);
A - This statement performs three actions in one.
The object is declared by notifying the compiler of the name of the object. The object is instantiated by using the new operator to allocate memory space to contain the new object. The object is initialized by making a call to the constructor named MyClass.
Q 28- In Java, if you attempt to instantiate an object and the Java Virtual Machine cannot allocate therequisite memory, the system will: ________________________________________.
A - Throw an OutOfMemoryError.
Q 29- The following is a valid method call: True or False. If false, explain why.
obj.myFunction(new myClassConstructor(1,2,3) );//Java version
A - True.
Q30 - In Java, when a method begins execution, all of the parameters are created as local automaticvariables: True or False? If false, explain why.
A - True.
Q31 - In the following statement, an object is instantiated and initialized and passed as a parameter to afunction. What will happen to that object when the function terminates?
obj.myFunction(new myClassConstructor(1,2,3) );//Java version
A - It will become eligible for garbage collection.
Q 32- In Java, you declare and implement a constructor just like you would implement any othermethod in your class, except that: _______________________________________________
A - you do not specify a return type and must not include a return statement.
Q33 - The name of the constructor must be the same as the name of the ___________________.
A - class.
Q 34- Usually in cases of inheritance, you will want the subclass to cause the constructor for thesuperclass to execute last to initialize those instance variables which derive from the superclass:True or False? If false, explain why.
A - False. You will want the subclass to cause the constructor for the superclass to execute first.
Q 35- Provide a code fragment that you would include at the beginning of your constructor for asubclass to cause the constructor for the superclass to be invoked prior to the execution of the bodyof the constructor.
A - super(optional parameters);
Q 36- Every object has a finalize method which is inherited from the class named ________________.
A - object.
Q 37- Before an object is reclaimed by the garbage collector, the _______________ method for theobject is called.
A - finalize
Q 38- In Java, the destructor is always called when an object goes out of scope: True or False? Iffalse, explain why.
A - False. Java does not support the concept of a destructor.
=====
Q 39- The class at the top of the inheritance hierarchy is the Object class and this class is defined in thepackage named java.Object: True or False? If false, explain why.
A - False. The Object class is defined in the package named java.lang.
Q40 - We say that an object has state and behavior: True or False? If false, explain why.
A - True.
Q 41- In Java, a method can be defined as an empty method, normally indicating that it is intended tobe overridden: True or False? If false, explain why.
A - True.
Q 42- Including an empty method in a class definition will make it impossible to instantiate an object ofthat class: True or False.
A - False.
Q 43- A subclass can invoke the constructor for the immediate superclass by causing the last line of ofthe subclass constructor to contain the keyword super followed by a parameter list as though callinga function named super() and the parameter list must match the method signature of the superclassconstructor: True or False? If false, explain why.
A - False. This can only be accomplished by causing the first line of the constructor to contain the keywordsuper followed by a parameter list as though calling a function named super(). The parameter list must match the method signature of the superclass constructor.
Q 43 The equals() method is used to determine if two reference variables point to the same object:True or False? If false, explain why.
A- False. You can use the equals() method to compare two objects for equality. You can use the equality operator (==) to determine if two reference variables point to the same object.
Q 44- The equals() method is used to determine if two separate objects are of the same type andcontain the same data. The method returns false if the objects are equal and true otherwise. Trueor False? If false, explain why.
A - False. The method returns true if the objects are equal and false otherwise.
Q 45 - The equals() method is defined in the Object class: True or False? If false, explain why.
A - True.
Q 46- Your classes can override the equals() method to make an appropriate comparison betweentwo objects of a type that you define: True or False? If false, explain why.
A - True.
Q 47- You must override the equals() method to determine if two string objects contain the same data:True or False? If false, explain why.
A - False. The system already knows how to apply the equals() method to all of the standard classes and objects of which the compiler has knowledge. For example, you can already use the method to test two String objects or two array objects for equality.
Q 48- Given an object named obj1, provide a code fragment that shows how to obtain the name of theclass from which obj1 was instantiated and the name of the superclass of that class.
A - See code fragment below:
System.out.println("Name of class for obj1: " + obj1.getClass().getName());
System.out.println("Name of superclass for obj1: " + obj1.getClass().getSuperclass());
Q 49- Given an object named obj2, provide a code fragment that shows how to use thenewInstance() method to create a new object of the same type
A - See code fragment below:
obj2 = obj1.getClass().newInstance();
Q 50- By overriding the getClass() method, you can use that method to determine the name of theclass from which an object was instantiated: True or False? If false, explain why.
A - False. The getClass() method is a final method and cannot be overridden.
Q 51- You must use the new operator to instantiate an object of type Class: True or False? If false,explain why.
A - False. There is no public constructor for the class Class. Class objects are constructed automatically by theJava Virtual Machine as classes are loaded and or by calls to the defineClass method in the class loader.
Q 52- The Class class provides a toString() method which can be used to convert all objects knownto the compiler to some appropriate string representation. The actual string representation dependson the type of object: True or False? If false, explain why.
A - False. The Object class (not the Class class) provides a toString() method which can be used to convert all objects known to the compiler to some appropriate string representation. The actual string representationdepends on the type of object.
Q 53- You can override the toString() method of the Class class to cause it to convert objects ofyour design to strings: True or False? If false, explain why.
A - False. The toString() method is a method of the Object class, not the Class class.
Q 54- By default, all classes in Java are either direct or indirect descendants of the Class class which isat the top of the inheritance hierarchy: True or False? If false, explain why.
A - False. By default, all classes in Java are either direct or indirect descendants of the Object class (not the Class class) which is at the top of the inheritance hierarchy.
=====
Q 55 - To a limited extent, the interface concept allows you to treat a number of objects, instantiatedfrom different classes, as if they were all of the same type: True or False? If false, explain why.
A - True.
Q 56- At its simplest level, an interface definition has a name, and declares one or more methods:True or False? If false, explain why.
A - True.
Q57- In an interface definition, both the method signatures and the actual implementations (bodies) ofthe methods are provided: True or False? If false, explain why.
A - False. Only the method signatures are provided. The actual implementations (bodies) of the methods are not provided.
Q 58- An interface definition can contain only method declarations: True or False? If false, explainwhy.
A - False. In addition to method declarations, an interface can also declare constants. Nothing else may beincluded inside the body of an interface definition.
Q59 - If classes P, D, and Q all implement interface X, a reference variable for an object of class P,D, or Q could be assigned to a reference variable of type X: True or False? If false, explain why.
A - True.
Q 60- If classes P, D, and Q all implement interface X, then all of the methods declared in X must beexactly the same in classes P, D, and Q: True or False? If false, explain why.
A - False. The interface simply declares the signatures for methods. Classes that implement the interface are free to provide a body for those methods which best suits the needs of the class.
Q 61- If classes P, D, and Q all implement interface X a reference variable for an object of class P,D, or Q could be assigned to a reference variable of type X and that reference variable could beused to access all of the methods of the class (which are not excluded using public, private, orprotected): True or False? If false, explain why.
A - False. If one or more of the classes P, D, and Q, define instance methods which are not declared in theinterface X, then a variable of type X cannot be used to access those instance methods. Those methods can only be accessed using a reference variable of the class in which the method is defined. Reference variables of the type X can only be used to access methods declared in the interface X (or one of its superinterfaces).
Q 61 - The new operator must be used to instantiate an object which is of the type of an interface: Trueor False? If false, explain why.
A - False. Even though you can consider the interface name as a type for purposes of storing references toobjects, you cannot instantiate an object of the interface type itself.
Q 63- One of the difficulties of implementing interfaces is the requirement to coordinate the definition ofinterface methods among the classes that implement the interface: True or False? If false, explainwhy.
A - False. In defining interface methods, each class defines the methods in a manner that is appropriate to its ownclass without concern for how it is defined in other classes.
Q 64- As with classes, multiple interface definitions can be combined into the same source file: True orFalse? If false, explain why.
A- False. The compiler requires interface definitions to be in separate files.
Q 65- List four ways in which interfaces are useful:
A - See the following list:
To a limited extent, the interface concept allows you to treat a number of objects, instantiated fromdifferent classes, as if they were all of the same type Capturing similarities between unrelated classes without forcing a class relationship Declaring methods that one or more classes are expected to implement Revealing an object's programming interface without revealing its class (objects such as these are calledanonymous objects and can be useful when shipping a package of classes to other developers)
Q 66- A minimum interface declaration contains the Java keyword interface, the name of theinterface, and the name of the interface that it extends: True or False? If false, explain why.
A - False. A minimum interface declaration contains the Java keyword interface and the name of the interface. There is no requirement to specify the name of the interface that it extends, because it may not extend another interface.
Q 67 - An interface can extend any number of other interfaces: True or False? If false, explain why.
A - True.
Q 68- Just like a class definition can extend any number of other classes, an interface can extend anynumber of other interfaces: True or False? If false, explain why.
A - False. A class can extend only one other class.
Q 69- An interface can extend any number of other interfaces but not more than one class: True orFalse? If false, explain why.
A - False. An interface cannot extend a class.
Q 70- An interface inherits all constants and methods from its superinterface: True or False? If false,explain why.
A - False. See reasons below:
An interface inherits all constants and methods from its superinterface unless:
the interface hides a constant with another of the same name, or redeclares a method with a new method declaration.
Q 71- The method declaration in an interface consists of the method signature followed by a pair ofempty curly braces: True or False? If false, explain why.
A - False. The method declaration is terminated by a semicolon and no body (no curly braces) is provided for the method.
Q 72- The keyword private is used to restrict access to the members of an interface only to classeswithin the same package: True or False? If false, explain why.
A - False. You may not use private in a member declaration in an interface.
Q 73- All methods declared in an interface are implicitly public and abstract: True or False? If false,explain why.
A - True.
Q 74- In addition to declaring methods, the body of the interface may also define constants. Constantvalues defined in an interface are implicitly public, static, and final: True or False? If false, explainwhy.
A - True.
Q 75- You use an interface by defining a class that extends the interface by name: True or False? Iffalse, explain why.
A - False. You use an interface by defining a class that implements (not extends) the interface by name.
Q 76- When a class claims to implement an interface, it must provide a full definition for all themethods declared in the interface as well as all of the methods declared in all of the superinterfacesof that interface: True or False? If false, explain why.
A - True.
Q 77- A class can implement more than one interface by including several interface names in acomma-separated list of interface names, and by providing a full definition for all of the methodsdeclared in all of the interfaces listed as well as all of the superinterfaces of those interfaces: True orFalse? If false, explain why.
A - True.
Q 78- Whenever a class implements an interface, it is allowed to define only those methods declared inthe interface: True or False? If false, explain why.
A - False. Whenever a class implements an interface, the class must define all of the methods declared in the interface, but is also free to define other methods as well.
Q 79- The definition of an interface is a definition of a new reference data type. You can use interfacenames just about anywhere that you would use other type names, except that you cannot____________________.
A - You cannot instantiate objects of the interface type.
Q 80- Explain in your own words the "bottom line" benefits of the use of an interface.
A - The interface makes it possible for a method in one class to invoke methods on objects of other classes,without the requirement to know the true class of those objects, provided that those objects are all instantiated from classes that implement one or more specified interfaces. In other words, objects of classes that implement specified interfaces can be passed into methods of other objects as the generic type Object, and the methods of the other objects can invoke methods on the incoming objects by first casting them as the interface type.
Q - The Java read() method reads and returns a single byte from the standard input device. Itstores that byte according to what type. What does the method return if the user enters an eof?
A - The Java read() method reads and returns a single byte from the standard input device and stores that bytein an integer. It returns an integer value of -1 if the user enters an eof.
Q - What keystroke combination can be used to simulate an eof at the keyboard of a DOS system?
A - An eof can be simulated on a DOS system keyboard by holding down the ctrl key and pressing the z key.
Q - Provide a Java code fragment illustrating how you would read a stream of bytes from thestandard input device until encountering an eof and quit reading when the eof is encountered.
A - The following Java code fragment will read a stream of bytes from the standard input device untilencountering an eof.
while(System.in.read() != -1) { //do something }
This code fragment accesses the read()method of the object referred to by the class variable named in of theclass named System.
Q - Provide a Java code fragment illustrating two different ways to display a String argument on theJava standard output device. Explain how your code works in object-oriented terms. Make certainthat you explain the difference between the two.
A - The following two code fragments will each display a string argument on the Java standard output device.System.out.println("String argument")
System.out.print("String argument")
In the first case, the code fragment accesses the println() method of the object referred to by the class variablenamed out of the class named System. In the second case, the print() method is accessed instead of the println() method.
The difference between the two is that the println() method automatically inserts a newlineat the end of thestring argument whereas the print() method leaves the display cursor at the end of the string argument. ===============OOP
Q - In Object-Oriented Programming, an object is often said to be an ____________ of a class.
A - An object is often said to be an instance of a class.
Q - In Object-Oriented Programming, an object is often said to have s_______ and b_______.Provide the missing words which begin with the letters shown.
A - In OOP, an object is often said to have state and behavior.
Q - An object's state is contained in its ________ and its behavior is implemented through its________. A - An object's state is contained in its member variables ( or data members) and its behavior is implemented through its methods ( or member functions).
Q - The member variables of an object can be either ____________ or _________ .
A - Its member variables can be either instance variables or class variables.
Q - What is generally meant by the terminology "sending a message to an object?"
A - We activate the behavior of an object by invoking one of its methods (sending it a message).
Q - What are the two things that can usually happen when an object receives a message?
A - When an object receives a message, it usually either performs an action, or modifies its state, or both.
Q - What happens to the memory occupied by an object in Java when the object is no longerneeded, and what do we normally do to make that happen?
A - When an object is no longer needed in Java, we simply forget it. Eventually, the garbage collector may (or may not) come by and pick it up for recycling.
Q - Identify as the stages of an object's life?
A - The stages of an Object's life are:
Creation Use Cleanup
Q - The creation of an object involves three steps (which are often combined). What are the three steps?
A - The three steps are:
declaration (providing a name for the object) instantiation (setting aside memory for the object) optional initialization (providing initial values for the object's instance variables)
Q - Java allows the instantiation of variables of primitive types in dynamic memory: True or False?If false, explain why and what you might be able to do to achieve almost the same result.
A - False. Java does not allow the instantiation of primitive variables in dynamic memory. (However, there are wrapper classes for primitive types which can be used to turn them into objects for this purpose.)
Q - An array of objects in Java is instantiated as an array of reference variables where eachreference variable can then be used to instantiate an object pointed to by the reference variable:True or False. If false, explain why and either provide a code fragment that illustrates your answer
A - True.
Q - In Java, it is always necessary to declare (give a name to) all new objects: True or False? Iffalse, explain why and either provide a code fragment that illustrates your answer
A - It is not always necessary in Java to declare an object (to give it a name). Consider, for example a case where anew object is instantiated to be used in an expression and there is no requirement to be able to access that object outside of the expression.
Q - Instance variables and instance methods can be accessed using an object as the accessmechanism. What is the difference in the syntax used to access an instance variable and aninstance method.
A - None. There is essentially no difference in the syntax used to access a variable or a method.
Q - Once you have instantiated an object, it is always possible to access all of the instancevariables and instance methods of that object by joining the name of the object to the name of thevariable or method using a period: True or False? If false, explain why.
A - False. Sometimes variables or methods may be hidden so as to make it impossible to access them. It is very common to hide the variables and to provide methods which can be accessed to serve as a pathway to the variables.
Q - Given an object named obj that has a public instance method named myMethod(), provide acode fragment that shows the proper syntax for accessing the method.
A - The proper syntax for accessing an instance method named myMethod() follows:
obj.myMethod()
Q - The object-oriented approach normally recommends hiding instance variables behind accessmethods: True or False? If true, explain why.
A - True. The object-oriented approach normally recommends hiding instance variables behind access methods. There are a variety of reasons why. One important reason is that hiding the instance variables makes it possible to later modify the implementation of instance variables to improve the behavior of objects of the class, without a requirement for modifying code that uses the clsss, provided that the access methods are not modified.
Q - The returning of memory (to the operating system) occupied by objects that are no longerneeded is automatically accomplished in Java by a feature commonly known as the____________________. A - The returning of memory to the operating system is taken care of automatically by a feature of Java known as the garbage collector.
Q - All necessary cleanup in a Java program is performed automatically by the garbage collector:True or False? If false, explain why.
A - False. Java does not support anything like a destructor that is guaranteed to be called whenever the object is no longer needed. Therefore, other than returning allocated memory, it is the responsibility of the programmer to explicitly perform any other required cleanup at the appropriate point in time.
Q - When does an object become eligible for garbage collection?
A - An object becomes eligible for garbage collection when there are no more references to that object.
Q - What can your program do to purposely make an object eligible for garbage collection.
A - Your program can make an object eligible for garbage collection by assigning null to all references to the object.
Q - The purpose of garbage collection in Java is to perform all necessary cleanup and the memoryoccupied by objects that are no longer needed will always be reclaimed by the garbage collector:True or False? If false, explain why.
A - False. The sole purpose of garbage collection is to reclaim memory occupied by objects that are no longer needed, and it has no other purpose relative to necessary cleanup. An object becomes eligible for garbage collection when there are no more references to that object. However, just because an object is eligible for garbage collection doesn't mean that it will be reclaimed. The garbage collector runs in a low-priority thread, and may not run at all unless a memory shortage is detected.
Q - Before the garbage collector reclaims the memory occupied by an object, it always calls theobject's _________ method. (Provide the name of the method.) Explain why this method is one ofthe methods in all new classes that you define.
A - Before the garbage collector reclaims the memory occupied by an object, it calls the object's finalizemethod. The finalize method is a member of the Object class. Since all classes inherit from the Object class, your classes also contain the default finalize method.
Q - What must you do to make effective use of the finalize method? Explain why you might want todo this.
A - In order to make use of the finalize method, you must override it, providing the code that you want to have executed before the memory is reclaimed.
Q - You can always be confident that the finalize method will be promptly executed to performnecessary cleanup in a Java program when an object becomes eligible for garbage collection: Trueor False? If false, explain why.
A - False. Although you can be confident that the finalize method will be called before the garbage collector reclaims the memory occupied by a particular object, you cannot be certain when, or if that memory will be reclaimed. There is no guarantee that the memory will be reclaimed by the garbage collector during the execution of your program.
Q - Provide a code fragment illustrating the method call that you can make to ask the garbagecollector to run. This guarantees that garbage collection will take place: True or False? If false,explain why.
A - False. Campione and Walrath indicate that you can ask the garbage collector to run at any time by calling the method shown below. They further point out, however, that making the request does not guarantee that your objects will be reclaimed through garbage collection. System.gc();

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Monday, May 01, 2006

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