User & Custom Defined Exceptions

User defined exceptions are those which are developed by JAVA programmer as a part of application development for dealing with specific problems such as negative salaries, negative ages, etc.

Guide lines fordeveloping userdefined exceptions:

Choose the appropriate package name.

Choose the appropriate user defined class.

Every user defined class which we have choose in step 2 must extends either java.lang.Exception or java.lang.RunTimeException class.

Every user defined sub-class Exception must contain a parameterized Constructor by taking string as a parameter.

Every user defined sub-class exception parameterized Constructor must called parameterized Constructor of either java.lang.Exception or java.lang.RunTimeException class by using super (string parameter always).

For example:

package na; // step1
public class Nage  extends Exception // step2 & step3
{
    public Nage (String s) // step4
    {
        super (s);// step5
    }
};

Write a JAVA program which illustrates the concept of user defined exceptions?

Answer:

package na;
public class Nage extends Exception
{
    public Nage (String s)
    {
        super (s);
    }
};

package ap;
import na.Nage;
public class Age
{
    public void decide (String s) throws NumberFormatException, Nage
    {
        int ag= Integer.parseInt (s); if (ag<=0)
        {
            Nage na=new Nage ("U HAV ENTERED INVALID AGE..!");
            throw (na);
        }
        else
        {
            System.out.println ("OK, U HAV ENTERED VALID AGE..!");
        }
    }
};

import na.Nage;
import ap.Age;
class CDemo
{
    public static void main(String[] args)
    {

        try
        {
            String s1=args [0];
            ap.Age Ao=new ap.Age ();
            Ao.decide (s1);
        }
        catch (Nage na)
        {
            System.out.println (na);
        }
        catch (NumberFormatException nfe)
        {
            System.out.println ("PASS ONLY INTEGER VALUES..!");
        }
        catch (ArithmeticException ae)
        {
            System.out.println ("PASS INTEGER VALUES ONLY..!");
        }
        catch (ArrayIndexOutOfBoundsException aioobe)
        {
            System.out.println ("PASS VALUES THROUGH COMMAND PROMPT..!");
        }
        catch (Exception e)
        {
            System.out.println (e);
        }
    }
};

Note:

Main method should not throw any exception since the main method is called by JVM and JVM cannot provide user friendly message.