Custom Exception in Java

Custom Exception in Java

If any exception is design by the user known as user defined or Custom Exception. Custom Exception is created by user.

Rules to design user defined Exception

1.     Create a package with valid user defined name.

2.     Create any user defined class.

3.     Make that user defined class as derived class of Exception or RuntimeException class.

4.     Declare parametrized constructor with string variable.

5.     call super class constructor by passing string variable within the derived class constructor.

6.     Save the program with public class name.java

Example

// save by AgeException.java

package nage;

public class AgeException extends Exception

{

public AgeException(String s)

{

super(s);

}

}

Compile: javac -d . AgeException.java

Example

// save by CheckAge.java

package nage;

public class CheckAge

{

public void verify(int age)throws AgeException

{

if (age>0)

{

System.err.print("valid age");

}

else

{

AgeException ae=new AgeException("Invalid age");

throw(ae);

}

}

}

Compile: javac -d . CheckAge.java

Example

// save by VerifyAgeException

import nage.AgeException;

import nage.CheckAge;

import java.util.*;

public class VerifyAgeException

{

public static void main(String args[])

{

int a;

System.out.println("Enter your age");

Scanner s=new Scanner(System.in);

a=s.nextInt();

try

{

CheckAge ca=new CheckAge();

ca.verify(a);

}

catch(AgeException ae)

{

System.err.println("Age should not be -ve");

}

catch(Exception e)

{

System.err.println(e);

}

}

}

Compile: javac VerifyAgeException.java

Steps to compile and run above program

First you save verify-age files into you PC in any where, here i will save this file in C:\>

·         C:\verify-age\>javac -d . AgeException.java

·         C:\verify-age\>javac -d . CheckAge.java

·         C:\verify-age\>javac VerifyAgeException.java

Note: First compile AgeException.java code then CheckAge.java and at last compile VerifyAgeException.java code.