Advanced Java Interview Question -7
1. 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.
2. What modifiers may be used with an interface declaration?
An interface may be declared as public or abstract.
3. Is a class a subclass of itself?
A class is a subclass of itself.
4. 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.
5. What event results from the clicking of a button?
The ActionEvent event is generated as the result of the clicking of a button.
6. 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.
7. 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.
8. 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.
9. 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.
10. What is the immediate superclass of Menu?
11. 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.
12. 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 accomodate platform-specific differences among windowing systems.
13. 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.
14. What modifiers can be used with a local inner class?
A local inner class may be final or abstract.
15. What Checkbox method allows you to tell if a Checkbox is checked?
16. What state is a thread in when it is executing?
An executing thread is in the running state.
17. 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.
18. What happens when you add a double value to a String?
The result is a String object.
19. 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.
20. Which package is always imported by default?
The java.lang package is always imported by default.
21. 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.
22. 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.
23. Can an abstract class be final?
An abstract class may not be declared as final.
24. 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.
25. What modifiers may be used with a top-level class?
A top-level class may be public, abstract, or final.
26. 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..
27. 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.
28. 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.
29. What methods are used to get and set the text label displayed by a Button object?
getLabel() and setLabel().
30. Which Component subclass is used for drawing and painting?
31. 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.
32. 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.
33. Name three subclasses of the Component class.
Box.Filler, Button, Canvas, Checkbox, Choice, Container, Label, List, Scrollbar, or TextComponent.
34. What is the GregorianCalendar class?
The GregorianCalendar class provides support for traditional Western calendars.
35. Which Container method is used to cause a container to be laid out and redisplayed?
validate() method is used to cause a container to be laid out and redisplayed.
36. What is the purpose of the Runtime class?
The purpose of the Runtime class is to provide access to the Java runtime system.
37. 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.
38. What is the return type of a program’s main() method?
A program’s main() method has a void return type.
39. Name four Container classes.
Window, Frame, Dialog, FileDialog, Panel, Applet, or ScrollPane.
40. 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.
41. What class of exceptions are generated by the Java run-time system?
The Java runtime system generates RuntimeException and Error exceptions.
42. What class allows you to read objects directly from a stream?
The ObjectInputStream class supports the reading of objects from input streams.
43. 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.
44. 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.
45. What are the high-level thread states?
The high-level thread states are ready, running, waiting, and dead.
46. 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.
47. Can a Byte object be cast to a double value?
No. An object cannot be cast to a primitive value.
48. 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.
49. What is the difference between the String and StringBuffer classes?
String objects are constants. StringBuffer objects are not constants.
50. 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.
51. What is an object’s lock and which object’s 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.
52. What is the Dictionary class?
The Dictionary class provides the capability to store key-value pairs.
53. 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.
54. 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.
55. 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.
56. 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.
57.What one should take care of while serializing the object?
One should make sure that all the included objects are also serializable. If any of the objects is not serializable then it throws a NotSerializableException.
58. What is a compilation unit?
A compilation unit is a Java source code file.
59. What interface is extended by AWT event listeners?
All AWT event listeners extend the java.util.EventListener interface.
60. 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.
61. How can a dead thread be restarted?
A dead thread cannot be restarted.
62. 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.
63. 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.
64. 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.
65. 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.
66. 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.
67. 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.
68. Why are the methods of the Math class static?
So they can be invoked as if they are a mathematical code library.
69. 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..
70. 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.
71. 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.
72. 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.
73. 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.
74. 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.
75. 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.
76. What is the argument type of a program’s main() method?
A program’s main() method takes an argument of the String type.
77. Which Java operator is right associative?
The = operator is right associative.
78. Can a double value be cast to a byte?
Yes, a double value can be cast to a byte.
79. 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.
80. Which class is the immediate superclass of the Container class?
81. 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.
82. How can the Checkbox class be used to create a radio button?
By associating Checkbox objects with a CheckboxGroup.
83. 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
84. What restrictions are placed on method overloading?
Two methods may not have the same name and argument list but different return types.
85. 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.
86. Does a class inherit the constructors of its superclass?
A class does not inherit constructors from any of its superclasses.
87. 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.
88. What is the purpose of the System class?
The purpose of the System class is to provide access to system resources.
89. Which TextComponent method is used to set a TextComponent to the read-only state?
90. 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.
91. Is &&= a valid Java operator?
No. It is not a valid java operator.
92. Name the eight primitive Java types.
The eight primitive types are byte, char, short, int, long, float, double, and boolean.
93. 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.
94. 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.
95. Is “abc” a primitive value?
The String literal “abc” is not a primitive value. It is a String object.
96. 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.
97. How is rounding performed under integer division?
The fractional part of the result is truncated. This is known as rounding toward zero.
98. 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.
99. 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.
100. What is the SimpleTimeZone class?
The SimpleTimeZone class provides support for a Gregorian calendar.
101. 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.
102. 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.