Question

public class A<T> {
    public <K> void m(A<K> target) {
        // determine if T equals K
    }
}

Is it possible to check if <T> and <K> are the same types?

Answer 1

Yes, this works the same way as the generic TypeReference. Normally types are erased but it works with anonymous inner classes:

public abstract class A<T> {

    private Type type;

    public A() {
        Type superclass = getClass().getGenericSuperclass();
        this.type = ((ParameterizedType) superclass).getActualTypeArguments()[0];
    }

    public <K> void m(A<K> target) {
            System.out.println( type.equals( target.type ) );
    }
}

To use it:

    A<String> as = new A<String>(){};
    A<String> a2s = new A<String>(){};
    A<Integer> ai = new A<Integer>(){};

    as.m(a2s); // prints true
    as.m(ai);  // prints false

The class does not have to be abstract but it serves as a reminder to make it anonymous inner class. The only real downside is that you have to put {} in the end.