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Java Interview Questions and Answers
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.
Can an abstract class be final?
An abstract class may not be declared as final.
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.
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.
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.
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.
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.
To what value is a variable of the boolean type automatically
initialized?
The default value of the boolean type is false.
Can try statements be nested?
Try statements may be tested.
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.
What is the purpose of a statement block?
A statement block is used to organize a sequence of statements as a
single statement group.
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.
What modifiers may be used with a top-level class?
A top-level class may be public, abstract, or final.
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.
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.
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.
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