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.
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
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 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
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 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
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 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
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 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
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 statement.
195. 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.
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.
