How to define custom exception class in Java, the easiest way?

I'm trying to define my own exception class the easiest way, and this is what I'm getting:

public class MyException extends Exception {}

public class Foo {
  public bar() throws MyException {
    throw new MyException("try again please");
  }
}

This is what Java compiler says:

cannot find symbol: constructor MyException(java.lang.String)

I had a feeling that this constructor has to be inherited from java.lang.Exception, isn't it?

Solution 1:

No, you don't "inherit" non-default constructors, you need to define the one taking a String in your class. Typically you use super(message) in your constructor to invoke your parent constructor. For example, like this:

public class MyException extends Exception {
    public MyException(String message) {
        super(message);
    }
}

Solution 2:

A typical custom exception I'd define is something like this:

public class CustomException extends Exception {

    public CustomException(String message) {
        super(message);
    }

    public CustomException(String message, Throwable throwable) {
        super(message, throwable);
    }

}

I even create a template using Eclipse so I don't have to write all the stuff over and over again.

Solution 3:

If you use the new class dialog in Eclipse you can just set the Superclass field to java.lang.Exception and check "Constructors from superclass" and it will generate the following:

package com.example.exception;

public class MyException extends Exception {

    public MyException() {
        // TODO Auto-generated constructor stub
    }

    public MyException(String message) {
        super(message);
        // TODO Auto-generated constructor stub
    }

    public MyException(Throwable cause) {
        super(cause);
        // TODO Auto-generated constructor stub
    }

    public MyException(String message, Throwable cause) {
        super(message, cause);
        // TODO Auto-generated constructor stub
    }

}

In response to the question below about not calling super() in the defualt constructor, Oracle has this to say:

Note: If a constructor does not explicitly invoke a superclass constructor, the Java compiler automatically inserts a call to the no-argument constructor of the superclass.

Solution 4:

Reason for this is explained in the Inheritance article of the Java Platform which says:

"A subclass inherits all the members (fields, methods, and nested classes) from its superclass. Constructors are not members, so they are not inherited by subclasses, but the constructor of the superclass can be invoked from the subclass."

Solution 5:

package customExceptions;

public class MyException extends Exception{

    public MyException(String exc)
    {
        super(exc);
    }
    public String getMessage()
    {
        return super.getMessage();
    }
}

import customExceptions.MyException;

public class UseCustomException {

    MyException newExc=new MyException("This is a custom exception");

    public UseCustomException() throws MyException
    {
        System.out.println("Hello Back Again with custom exception");
        throw newExc;       
}

    public static void main(String args[])
    {
        try
        {
            UseCustomException use=new UseCustomException();
        }
        catch(MyException myEx)
        {
            System.out.println("This is my custom exception:" + myEx.getMessage());
        }
    }
}