Wednesday, 23 May 2012

Exception Interview Questions with answers

Exception Interview Questions

1) What is an Exception?
An exception is an abnormal condition that arises in a code sequence at run time. In other
words, an exception is a run-time error.

2) What is a Java Exception?
A Java exception is an object that describes an exceptional condition i.e., an error condition
that has occurred in a piece of code. When this type of condition arises, an object
representing that exception is created and thrown in the method that caused the error by
the Java Runtime. That method may choose to handle the exception itself, or pass it on.
Either way, at some point, the exception is caught and processed.

3) What are the different ways to generate and Exception?
There are two different ways to generate an Exception.
1. Exceptions can be generated by the Java run-time system.
Exceptions thrown by Java relate to fundamental errors that violate the rules of the
Java language or the constraints of the Java execution environment.
2. Exceptions can be manually generated by your code.
Manually generated exceptions are typically used to report some error condition to
the caller of a method.

4) Where does Exception stand in the Java tree hierarchy?
• java.lang.Object
• java.lang.Throwable
• java.lang.Exception
• java.lang.Error

5) Is it compulsory to use the finally block?
It is always a good practice to use the finally block. The reason for using the finally block is,
any unreleased resources can be released and the memory can be freed. For example while
closing a connection object an exception has occurred. In finally block we can close that
object. Coming to the question, you can omit the finally block when there is a catch block
associated with that try block. A try block should have at least a catch or a finally block.

6) How are try, catch and finally block organized?
A try block should associate with at least a catch or a finally block. The sequence of try,
catch and finally matters a lot. If you modify the order of these then the code won’t
compile. Adding to this there can be multiple catch blocks associated with a try block. Thefinal concept is there should be a single try, multiple catch blocks and a single finally block
in a try-catch-finally block.

7) What is a throw in an Exception block?
“throw” is used to manually throw an exception (object) of type Throwable class or a
subclass of Throwable. Simple types, such as int or char, as well as non-Throwable
classes, such as String and Object, cannot be used as exceptions. The flow of execution
stops immediately after the throw statement; any subsequent statements are not
throw ThrowableInstance;
ThrowableInstance must be an object of type Throwable or a subclass of Throwable.
throw new NullPointerException("thrownException");

8) What is the use of throws keyword?
If a method is capable of causing an exception that it does not handle, it must specify this
behavior so that callers of the method can guard themselves against that exception. You do
this by including a throws clause in the method’s declaration. A throws clause lists the
types of exceptions that a method might throw.
type method-name(parameter-list) throws exception-list
// body of method
Warning: main(
failed to open stream: HTTP request failed! HTTP/1.1 404 Not Found in
/home/content/k/k/s/kkskrishna/html/faqs/exception/exception-faqs-1.html on line 195
Warning: main(
failed to open stream: HTTP request failed! HTTP/1.1 404 Not Found in
/home/content/k/k/s/kkskrishna/html/faqs/exception/exception-faqs-1.html on line 195
Warning: main(): Failed opening '' for inclusion
(include_path='.:/usr/local/lib/php') in /home/content/k/k/s/kkskrishna/html/faqs/exception/exception-faqs-1.html
on line 195
Here, exception-list is a comma-separated list of the exceptions that a method can throw.
static void throwOne() throws IllegalAccessException {
System.out.println("Inside throwOne.");

9) What are Checked Exceptions and Unchecked
The types of exceptions that need not be included in a methods throws list are called
Unchecked Exceptions.
• ArithmeticException
• ArrayIndexOutOfBoundsException
• ClassCastException
• IndexOutOfBoundsException
• IllegalStateException
• NullPointerException
• SecurityException
The types of exceptions that must be included in a methods throws list if that method can
generate one of these exceptions and does not handle it itself are called Checked
• ClassNotFoundException
• CloneNotSupportedException
• IllegalAccessException
• InstantiationException
• InterruptedException
• NoSuchFieldException
• NoSuchMethodException

10) What are Chained Exceptions?
The chained exception feature allows you to associate another exception with an exception.
This second exception describes the cause of the first exception. Lets take a simple
example. You are trying to read a number from the disk and using it to divide a number.
Think the method throws an ArithmeticException because of an attempt to divide by zero
(number we got). However, the problem was that an I/O error occurred, which caused the
divisor to be set improperly (set to zero). Although the method must certainly throw an
ArithmeticException, since that is the error that occurred, you might also want to let the
calling code know that the underlying cause was an I/O error. This is the place where
chained exceptions come in to picture.
Throwable getCause( )
Throwable initCause(Throwable causeExc)

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