Find out if .class file implements interface

Question

Given the path to a class file, how can I find out if it implements a certain interface?

I could use javap and parse the output, but there are probably more intelligent ways.

I do not want to parse the source code because it may not be available. I should also note that the path of the class file will be available only at runtime.

Can't you load that class and use something like [this](http://stackoverflow.com/questions/6616055/get-all-derived-interfaces-of-a-class) to get all interfaces — TheLostMind, Nov 18 '15 at 07:56
@ParkerHalo: not really a duplicate. here the question is about the class, there it was about parsing through source code itself — Stultuske, Nov 18 '15 at 07:59
@VinodMadyalkar: that's overkill. for one specific interface, an instanceof check will do. — Stultuske, Nov 18 '15 at 08:00
It is easier to use `isAssignableFrom` when you have two classes. http://stackoverflow.com/a/3949379/1651233 — BobTheBuilder, Nov 18 '15 at 08:02
@Stultuske - Yes. Probably. `instanceof` would not be a bad idea here :) — TheLostMind, Nov 18 '15 at 08:49

score 0 · Accepted Answer · answered Nov 18 '15 at 08:57

If you need to check it from the command line then javap is an option.

If you need to check it from within the code this should work

interface MyInterface {
    ...
}
try {
    URL classUrl;
    classUrl = new URL(<path to the dir containg the .class file>); 

    URL[] classUrls = { classUrl };
    URLClassLoader ucl = new URLClassLoader(classUrls);

    Class clazz = ucl.loadClass(<your class name>); 
    if (MyInterface.class.isInstance(clazz.newInstance())){
        ...
    }
}
catch (Exception e){ System.out.println(e);}

Kumar Saurabh · Answer 2 · 2015-11-18T08:49:19.770

-1

Let us assume Class A implements Interface B

To check that you can use InstanceOf operator

A a = new A();
if(a instanceof B)  // here a is refernce variable holding object of class A
{
//do your thing
}

EDIT

Class clazz = (Class) Class.forName("Your class name");
for (Class c : clazz.getClass().getInterfaces()) {
   String name=c.getName());
   if(name.equals("org.apache.SomethingInterface"))
    {
     now u know u have it implemented
    }
}

edited Nov 18 '15 at 08:49

answered Nov 18 '15 at 07:57

Kumar Saurabh

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don't you mean: new A() instanceof B ? – Stultuske Nov 18 '15 at 07:58
thanks for pointing that out, I missed that – Kumar Saurabh Nov 18 '15 at 07:59
How do I do such a check if I only know the class file at runtime? – J Fabian Meier Nov 18 '15 at 08:10
do you mean the name of class/interFace? – Kumar Saurabh Nov 18 '15 at 08:10
At runtime, I get a path to a class file. I want to find out if this class file implements an interface. – J Fabian Meier Nov 18 '15 at 08:12
@JFMeier: something like ( a.getClass() instanceOf atRuntimeKnown.getClass()) or similar – Stultuske Nov 18 '15 at 08:12
Or use can use Class.Forname(name of class in string ) to to get a class type object of that class – Kumar Saurabh Nov 18 '15 at 08:13
I don't get it: Assume I am given "C:\bio.class" and want to find out if it implements "org.apache.SomethingInterface", what do I do? – J Fabian Meier Nov 18 '15 at 08:15
i edit the answer I dont have a editor right now so didnt tested for exact syntax, but idea is simiar – Kumar Saurabh Nov 18 '15 at 08:50

Find out if .class file implements interface

2 Answers2