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Exceptions

Mr.Prasad SawantDepartment Of Computer Science

Prof .Ramkurshana More Arts, Commerce and Science College Akurdi. Mobile :9665755707Email:[email protected]

Blog:http://prasadmsawant.blogspot.com/

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Agenda

Define exception. Discuss what is meant by exception

handing.

Describe the try,catch and finallyblocks.

Examine multiple catch blocks.

Explore nested try catch blocks. Explain the use of throw and throws

keywords.

Create user defined exception.

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What is exception?

When an error is encountered duringthe execution of a program an

exception is said to have occurred.

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Handling Exception

…

IF B IS ZERO GO TO EROR

C=A/B

PRINT C

GO TO EXITERROR:

DISPLAY “CODE CAUSING ERROR DUE TODIVISION BY ZERO”

EXIT:

END

BLOCKTHAT

HANDLES

ERROR

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HANDLING EXCEPTION IN

JAVAOBJECT

THROWABLEError Exception

AWT ERROR

Thread Death..

………

SQLException

ClassNotFoundException

………

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System-Defined Exception

Raised implicitly by system because ofillegal execution of program

When cannot continue program

execution any more Created by Java System automatically

Exception extended from Error class

and RuntimeException class

[DivByZero.java]

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IndexOutOfBoundsException :◦ When beyond the bound of index in the object which use

index, such as array, string, and vector

ArrayStoreException :◦ When assign object of incorrect type to element of array

NegativeArraySizeException :◦ When using a negative size of array

NullPointerException : ◦ When refer to object as a null pointer

SecurityException :

◦ When violate security. Caused by security manager

IllegalMonitorStateException :◦ When the thread which is not owner of monitor involves wait

or notify method

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Programmer-Defined Exception

Exceptions raised by programmer

Check by compiler whether the

exception handler for exception

occurred exists or not

◦ If there is no handler, it is error

Sub class of Exception class

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The exception handling model

try

{

// code which is expected to throw an exception

}

Catch (exception e1){

/*

If exception is thrown in the try block ,is of typee1,then perform necessary action here

*/

}

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Multiple catch block

Class catch22{

public static void main(String args[])

{

try

{

String num=args[0];

int numValue=Interger.parseInt(num);System.out.println(“The squre is ”+numValue*numvalue”);

}

catch(ArrayIndexOutOfBoundException e1)

{

System.out.println(“No argument is given!”);

}

catch(NumberFormatException e2){

System.out.println(“Not a number “);

}

}

}

C:>javac catch22

No argument is given!

C:>javac catch22 a

Not a number

C:>javac catch22 3

The squre is 9

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Nested try-catch

… try

{

int num=args.length;

try

{

int numValue=Integer.parseInt(args[0]);System.out.println(“The squre is “+numValue*numValue);

}

catch(NumberFormatExcption e1)

{

System.out.println(“Not a Number!”);

}

}

catch (ArrayIndexOutOf BoundException e2)

{

System.out.println(“No arguments given!”);

}

….

C:>javac catch

No argument is given!

C:>javac catch22 a

Not a number

C:>javac catch22 3

The squre is 9

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Finally block

The ‘finally ’block is guaranteed to run whether or notan exception occurs. The finally clauses of a try catchblock will always execute ,even if there are returnstatement in the try catch part .

Try block

finally Catch block

finally

No exception Exception

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Using throws and throw

Exception are thrown with the help of the „throw‟ keyword .The „throw‟ keyword isused to indicate that an exception hasoccurred .The operand of throw is an object

of any class that is derived from the class‟ Throwable‟.

The throws keyword is used to list theexception that method can throw.

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