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.
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