How to check if an object implements an interface?

Question

How to check if some class implements interface? When having:

Character.Gorgon gor = new Character.Gorgon();

how to check if gor implements Monster interface?

public interface Monster {

    public int getLevel();

    public int level = 1;
}

public class Character {
    public static class Gorgon extends Character implements Monster {
        public int level;
        @Override
        public int getLevel() { return level; }

        public Gorgon() {
            type = "Gorgon";
        }
    }
}

Is the method getLevel() overridden in Gorgon correctly, so it can return level of new gor created?

I think you Need the instanceof keyword. – Martin Röbert Apr 15 '12 at 20:43 — Martin Röbert, Apr 15 '12 at 20:43

score 250 · Accepted Answer · answered Apr 15 '12 at 20:43

250

For an instance

Character.Gorgon gor = new Character.Gorgon();

Then do

gor instanceof Monster

For a Class instance do

Class<?> clazz = Character.Gorgon.class;
Monster.class.isAssignableFrom(clazz);

answered Apr 15 '12 at 20:43

Mike Q

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How about method parameter `public void doSomething([Object implements Serializable] param)`? What's the right syntax for that? – Tomáš Zato Mar 26 '15 at 00:35
1

Yeh, `...isAssignableFrom()`, the only way to determine a Gorgonite is a monster. – Joe Almore Dec 09 '16 at 12:58

score 46 · Answer 2 · answered Apr 15 '12 at 20:43

46

Use

if (gor instanceof Monster) {
    //...
}

answered Apr 15 '12 at 20:43

krock

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This answer is useful for users who don't have any complex inner classes or that stuff. Good job. – Macintosh Fan Aug 22 '21 at 19:05

score 35 · Answer 3 · answered Apr 18 '16 at 06:43

35

In general for AnInterface and anInstance of any class:

AnInterface.class.isAssignableFrom(anInstance.getClass());

answered Apr 18 '16 at 06:43

Oleg Mikhailov

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score 1 · Answer 4 · answered Dec 06 '15 at 11:57

If you want a method like public void doSomething([Object implements Serializable]) you can just type it like this public void doSomething(Serializable serializableObject). You can now pass it any object that implements Serializable but using the serializableObject you only have access to the methods implemented in the object from the Serializable interface.

How to check if an object implements an interface?

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