CODEWITHSUNDEEP
java
Anil Kumar C
Anil Kumar C

Reputation: 1624

can we write custom marker interfaces

I want to write my own marker interfaces like java.io.Serializable or Cloneable which can be understandable to JVM. Please suggest me the implementation procedure.

For example I implemented a interface called NotInheritable and all the classes implementing this interface has to avoid inheritance.

Upvotes: 7

Views: 17630

Answers (5)

Vijay Bhatt
Vijay Bhatt

Reputation: 1391

Yes We can write our own marker exception.... see following example....

interface Marker{   
}

class MyException extends Exception {   

    public MyException(String s){
        super(s);
    }
}

class A implements Marker {

   void m1() throws MyException{        
     if((this instanceof Marker)){
         System.out.println("successfull");
     }
     else {
         throw new MyException("Unsuccessful  class must implement interface Marker ");
     }      
}   
}

/* Class B has not implemented Maker interface .
 * will not work & print unsuccessful Must implement interface Marker
*/
class B extends A  {    


}

// Class C has not implemented Maker interface . Will work & print successful

public class C  extends A implements Marker   
 { // if this class will not implement Marker, throw exception
     public static void main(String[] args)  {
     C a= new C();
     B b = new B();

     try {
        a.m1(); // Calling m1() and will print
        b.m1();
     } catch (MyException e) {

        System.out.println(e);
    }

}
}

OUTOPUT

Upvotes: 2

Kumar Nishant
Kumar Nishant

Reputation: 11

suppose myMethod should be called only if marker MyInterface should be marked there.

interface MyInterface{}

class MyException extends RuntimeException{

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

class MyClass implements MyInterface{
    public void myMethod(){
        if(!(this instanceOf MyInterface)){
            throw new MyException();
        }else{
            // DO YOUR WORK
        }
    }
}

Upvotes: 1

Marko Topolnik
Marko Topolnik

Reputation: 200158

public interface MyMarkerInterface {}

public class MyMarkedClass implements MyMarkerInterface {}

Then you can for example have method taking only MyMarkerInterface instance:

public myMethod(MyMarkerInterface x) {}

or check with instanceof at runtime.

Upvotes: 3

Balaswamy Vaddeman
Balaswamy Vaddeman

Reputation: 8530

You can write your own Marker interface ,JVM do not know anything about it.

You have to provide functionality by using instanceof. check this

Upvotes: 0

Damian Leszczyński - Vash
Damian Leszczyński - Vash

Reputation: 30865

A marker interface is an empty interface. This mean you just need to create a interface and do not create any method in it. Better explanation you will find here.

This approach can be replaced with Annotations that have similar functionality over types. more

Upvotes: -3

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