Frequently Asked Questions on Java

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. 

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.

What is the Dictionary class?
The Dictionary class provides the capability to store key-value pairs.

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.

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.

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.

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.

Which class is extended by all other classes? 
The Object class is extended by all other classes. 

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..

Is the ternary operator written x : y ? z or x ? y : z ? 
It is written x ? y : z. 

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.

How is rounding performed under integer division?
The fractional part of the result is truncated. This is known as rounding toward zero.

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.

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.

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.

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.

What is the SimpleTimeZone class?
The SimpleTimeZone class provides support for a Gregorian calendar.

What is the Map interface?
The Map interface replaces the JDK 1.1 Dictionary class and is used associate keys with values.

Does a class inherit the constructors of its superclass?
A class does not inherit constructors from any of its superclasses.

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.

More Java Questions

Do you have a Java Problem?
Ask It in The Java Forum

Java Books
Java Certification, Programming, JavaBean and Object Oriented Reference Books

Return to : Java Programming Hints and Tips

All the site contents are Copyright © www.erpgreat.com and the content authors. All rights reserved.
All product names are trademarks of their respective companies.
The site www.erpgreat.com is not affiliated with or endorsed by any company listed at this site.
Every effort is made to ensure the content integrity.  Information used on this site is at your own risk.
 The content on this site may not be reproduced or redistributed without the express written permission of
www.erpgreat.com or the content authors.