Access static method on generic class

Question

I'd like to access a static method on a class, but have that class passed in a generic.

I've done the following:

class Base{
  public static String getStaticName(){
    return "Base";
  }
}


class Child extends Base{
  public static String getStaticName(){
    return "Child";
  }
}

class StaticAccessor{
  public static <T extends Base>String getName(Class<T> clazz){
    return T.getStaticName();
  }
}

StaticAccessor.getName() // --> "Base"

This will return "Base" but what i'd like is "Child" anybody a suggestion without reflections?

Joachim Sauer · Accepted Answer · 2011-05-05 12:17:08Z

9

You can't do that without reflection, because the type T is erased at runtime (meaning it will be reduced to its lower bound, which is Base).

Since you do have access to a Class<T> you can do it with reflection, however:

return (String) clazz.getMethod("getStaticName").invoke(null);

Note that I'd consider such code to be code smell and that it is pretty fragile. Could you tell us why you need that?

answered May 5, 2011 at 12:17

Joachim Sauer

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4 Comments

Nathan Ryan Over a year ago

Simpler: return clazz.getSimpleName();

Joachim Sauer Over a year ago

@Nathan: yes, if the implementation will always look like that.

Nathan Ryan Over a year ago

correct. My suggestion works only if the intention of the getStaticName() method is to return the simple (or binary/canonical) name of the class.

TommasoF Over a year ago

@joachimSauer could you please explain better "...the type T is erased at runtime".

Jérôme Verstrynge · Accepted Answer · 2011-05-05 12:30:45Z

0

If it is OK for you to pass an object instance rather than Class in your static accessor, then, there is a simple and elegant solution:

public class Test {

    static class Base {
        public static String getStaticName() { return "Base"; }
        public String myOverridable() { return Base.getStaticName(); };
    }

    static class Child extends Base {
        public static String getStaticName() { return "Child"; }
        @Override
        public String myOverridable() { return Child.getStaticName(); };
    }

    static class StaticAccessor {
        public static <T extends Base>String getName(T instance) {
            return instance.myOverridable();
    }

}


    public static void main(String[] args) {

        Base b = new Base();
        Child c = new Child();

        System.out.println(StaticAccessor.getName(b));
        System.out.println(StaticAccessor.getName(c));

    }

}

The output is:

Base
Child

answered May 5, 2011 at 12:30

Jérôme Verstrynge

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3 Comments

planetjones Over a year ago

Yep this is just using polymorphism though to get the Name. The original example seemed to imply it should work without any Object instances and work just against the Class. I guess in the example you could just call the getName method on the object instance itself.

Jérôme Verstrynge Over a year ago

@planetjones No, you cannot call getStaticName() on the instance itself, because it would only return 'Base' in both cases.

planetjones Over a year ago

oh sorry I meant to say call the method against the Object i.e. myOverridable() could be called directly against b or c.

Peter Lawrey · Accepted Answer · 2011-05-05 12:57:35Z

0

I don't believe you can do this without reflection.

It appears you should be doing is not using static methods. You are using inheritance but static methods do not follow inheritance rules.

answered May 5, 2011 at 12:57

Peter Lawrey

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