How to check if a class implements a interface [duplicate]

Question

here we go,

I have an marker interface :

interface IPOJO {
}

And then i have a class implementing this interface :

class MePOJO implements IPOJO {
}

Now suppose i have a class object holding reference of class MePOJO :

Class<MePOJO> classObj = MePOJO.class;

So how can i determine if MePOJO class implements IPOJO just by using classObj ?

Answer 1

You should use Class#isAssignableFrom(Class<?> cls) method here:

Class<?> classObj = MePOJO.class;
System.out.println(IPOJO.class.isAssignableFrom(classObj));

Output:

true

Answer 2

There are several approaches for this.

Either by using the Class type of the object you've created and retrieve the list with all the interfaces that it implements.

MePOJO test = new MePOJO();
Class[] interfaces = test.getClass().getInterfaces();
for (Class c : interfaces) {
   if ("IPOJO".equals(c.getSimpleName()) {
      System.out.println("test implements IPOJO");
   }
}

Or using the Class#isAssignableFrom(Class clazz) method:

Class<?> clazz = MePOJO.class;
System.out.println(IPOJO.class.isAssignableFrom(clazz));