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SCJP Tutorial -- Exception Handling

Tags: exception
Exception Handling



Defination :-
An exception is an event that occurs during the execution of a program that disrupts the normal flow of instructions.

There are 3 main advantages for exceptions:
1. Separates error handling code from "regular" code
2. Propagating errors up the call stack (without tedious programming)
3. Grouping error types and error differentiation


Syntax :-


try {

int y =5;

for(int i =5; i

{ int z = x/i; }

}catch(Exception e1)

{ system.out.println( "Exception Occured" +e.printstacktrace());

}

finally {

System.out.println("Fional code is always executed");

}


Important tricks to be Noted :-

" An exception causes a jump to
the end of try block. If the exception occurred in a method called from a try
block, the called method is abandoned.


******************************************************************************************************


" If there's a catch block for
the occurred exception or a parent class of the exception, the exception is now
considered handled.

*******************************************************************************************************

" At least one 'catch' block or one 'finally' block
must accompany a 'try' statement. If all 3 blocks are present, the order is
important. (try/catch/finally)

*******************************************************************************************************

" finally and catch can come only with
try, they cannot appear on their own.

****************************************************************************************************

" Regardless of whether or not an
exception occurred or whether or not it was handled, if there is a finally
block, it'll be executed always. (Even if there is a return statement in try
block).

**************************************************************************************************

" System.exit() and error conditions are the only exceptions
where finally block is not executed.

****************************************************************************************************

" If there was no exception or the
exception was handled, execution continues at the statement after the
try/catch/finally blocks.

****************************************************************************************************

" If the exception is not handled, the process
repeats looking for next enclosing try block up the call hierarchy. If this
search reaches the top level of the hierarchy (the point at which the thread was
created), then the thread is killed and message stack trace is dumped to
System.err.

****************************************************************************************************

" Use throw new xxxException() to throw an exception. If the
thrown object is null, a NullPointerException will be thrown at the handler.

****************************************************************************************************

" If an exception handler re-throws an exception (throw in a catch
block), same rules apply. Either you need to have a try/catch within the catch
or specify the entire method as throwing the exception that's being re-thrown in
the catch block. Catch blocks at the same level will not handle the exceptions
thrown in a catch block - it needs its own handlers.

****************************************************************************************************

" The method
fillInStackTrace() in Throwable class throws a Throwable object. It will be
useful when re-throwing an exception or error.

****************************************************************************************************

" The Java language
requires that methods either catch or specify all checked exceptions that can be
thrown within the scope of that method.

****************************************************************************************************

" All objects of type
java.lang.Exception are checked exceptions. (Except the classes under
java.lang.RuntimeException) If any method that contains lines of code that might
throw checked exceptions, compiler checks whether you've handled the exceptions
or you've declared the methods as throwing the exceptions. Hence the name checked exceptions.

****************************************************************************************************

" If there's no
code in try block that may throw exceptions specified in the catch blocks,
compiler will produce an error. (This is not the case for super-class Exception)

****************************************************************************************************

" Java.lang.RuntimeException and java.lang.Error need not be handled or
declared.

****************************************************************************************************



Classification of Exception:


Exception-->ClassNotFoundException, ClassNotSupportedException, IllegalAccessException, InstantiationException, IterruptedException, NoSuchMethodException, RuntimeException, AWTException, IOException

RuntimeException-->EmptyStackException, NoSuchElementException, ArithmeticException, ArrayStoreException, ClassCastException, IllegalArgumentException, IllegalMonitorStateException,
IndexOutOfBoundsException, NegativeArraySizeException, NullPointerException, SecurityException.

IllegalArgumentException-->IllegalThreadStateException, NumberFormatException

IndexOutOfBoundsException-->ArrayIndexOutOfBoundsException, StringIndexOutOfBoundsException

IOException-->EOFException, FileNotFoundException, InterruptedIOException, UTFDataFormatException, MalformedURLException, ProtocolException, SockException, UnknownHostException, UnknownServiceException.


This post first appeared on SCJP Tutorial -1.5 Tips And Tricks, please read the originial post: here

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SCJP Tutorial -- Exception Handling

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