Core
Java
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,
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.
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
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.
23What 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 wrapped classes?
Wrapped 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
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 an 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
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
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 intialization 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 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.
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
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
superclasses.
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 &&= 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
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 accomodate
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
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
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
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
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
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
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
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
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 statement.
195. What are the two basic ways in which classes that can
be run as threads
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.
198. What happens when you add a double value to a
String?
The result is a String object.
199. What is the List interface?
The List interface provides support for ordered collections
of objects.