java - Loading a Class from a String

Question

I want to instantiate a class by the value of a String. I found several tutorials that show several methods for doing this. The class MUST inherit from a certain interface, ImplementMe which has a special method called runMe(). So here's what I tried:

ImplmentMe a =
   (ImplementMe) ImplementMe.class
                   .getClassLoader()
                   .loadClass("my.package.IImplementedYou")
                   .newInstance();
a.runMe();

It works, but it's so ugly. I at least expected not needing a cast. Please tell me there is a better way.

Answer 1

No, there is no better way (by design). You are not supposed to do this, Java is designed as a type-safe language. However, I can understand that you sometimes need to do things like this, and for that purposes you can create a library function like this:

public <T> T instantiate(final String className, final Class<T> type){
    try{
        return type.cast(Class.forName(className).newInstance());
    } catch(InstantiationException
          | IllegalAccessException
          | ClassNotFoundException e){
        throw new IllegalStateException(e);
    }
}

Now your client code can at least call this method without casting:

MyInterface thingy =
    instantiate("com.foo.bar.MyInterfaceImpl", MyInterface.class);