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.
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.
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