OverridingAndExceptions.java

/**
 * Rule #1:
 * If the super-class overridden method does not throw an exception, 
 * subclass overriding method can only throws the unchecked exception, 
 * throwing checked exception will lead to compile-time error.
 * 
 * Rule #2:
 * If the super-class overridden method does throws an exception, subclass 
 * overriding method can only throw same, subclass exception. Throwing parent 
 * exception in Exception hierarchy will lead to compile time error. Also there 
 * is no issue if subclass overridden method is not throwing any exception.
 * 
 */

class ParentClass {
    void method1 () {
        System.out.println("parent method1");
    }

    void method2 () {
        System.out.println("parent method1");
    }

    void method3 () throws RuntimeException{
        System.out.println("parent method3");
    }
}

class ChildClass {

    @Override
    void method1 () throws ArithmeticException{
        System.out.println("child method1");
    }

    // Throwing checked exception will give compilation error
    // @Override
    // void method2 () throws Exception
    //     System.out.println("child method2");
    // }

    /**
     * This method can throw the same exception (RunTimeException), can throw subclass of
     * the parent thrown exception like (ArithmaticException), can throw no exceptions but 
     * it can't throw parent of RunTimeException (Here) in exception hierarchy (e.g. Exception). 
     * This  will give compilation error.
     */
    @Override
    void method3 () {
        System.out.println("child method3");
    }
}