125. 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.
126. Which class is the immediate superclass of
the Container class? Component
127. 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 is the List interface?
The List interface provides
support for ordered collections of objects.