Making Custom (User Defined) Exceptions
<<<<<<< making_custom.shtml
Making Custom (User Define Exceptions)
So far you would have been known, how to be handled the exceptions in java
=======
So far you would have been known, how to be handled the exceptions in java
>>>>>>> 1.3
that are thrown by the Java API but sometimes you may occasionally need to throw
your own exception i.e. if you encounter a situation where none of those
exception describe your exception accurately or if you can't find
the appropriate exception in the Java API, you can code a class that defines an
exception that is more appropriate and that mechanism of handling exception is
called Custom or User Defined Exception.
In Java API all exception classes have two type of constructor. First is
called default constructor that doesn't accept any arguments. Another
constructor accepts a string argument that provides the additional information
about the exception. So in that way the Custom exception behaves like the
rest of the exception classes in Java API.
There are two primary use cases for a custom exception.
- your code can simply throw the custom exception when something goes
wrong.
- You can wrap an exception that provides extra information by adding
your own message.
The code of a Custom exception:
|
public
class ExceptionClassName extends Exception
{
public ExceptionClassName(){ }
public ExceptionClassName(StringMessage)
{
super(message);
}
}
|
Lets see an example that has the
implementation of User Define Exception:
import java.io.*;
import java.util.*;
class MyException extends Exception
{
private String nm="";
public String getMessage(String
s)
{
nm=s;
return ("you are not permitted to enter
inside "+nm);
}
}
public class ExcepDemo
{
public static void main(String args[])throws MyException,IOException
{
String temp="";
try
{
String str="amit";
System.out.println("Enter the your name");
BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
temp=br.readLine();
if(!temp.equals(str))
throw new MyException();
else
System.out.println("Welcome to Rose
India");
}
catch(MyException e)
{
System.err.println(e.getMessage(temp));
}
catch(Exception e){
System.err.println(e);
}
}
} |
Output of the program:
| C:\Roseindia\>javac
ExcepDemo.java
C:\Roseindia\>java ExcepDemo
Enter the your name
nisha
you are not permitted to enter inside nisha
C:\Roseindia\>java ExcepDemo
Enter the your name
amit
Welcome to Rose India
|
In this example we have created own exception class as MyException
that throws an exception and a function with argument as getMessage that
shows an exception message, if the user tries to enter the another name which
doesn't match with a particular predefined name. After throwing exception
the control will be transferred in the catch block to handle the exception where the
function is invoked to display the message included in that function.
Download this example
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