Question

I am using generics in my class. MyObject must use T as an class, e.g. new MyObject(Long.class). In the method equal I want to ensure that the argument given to the method is an instance of T.

Object<T> is not a valid Java Source, I know.
I added it to the code example to show you what I mean, i.e. that value is an instance of T.

But what is the correct way to implement the equal method??

public class MyObject<T extends Class> {

    public boolean equal(Object<T> value) {
        return true;
    }
}

Answer 1

Assuming that you’re not out to override Object.equals(Object):

T extends Class makes scant sense because Class is final anyway, so the only thing T could be would be Class<U> for some U, and then you might as well let U be the type parameter. So what you might want it something like:

public class MyClass<T> {
  private Class<T> cl ;
  public MyClass(Class<T> cl) {
    this.cl = cl ;
    ...
  }
  public boolean equal(T value) {
    return true;
  }
}

and you then get to write, say, new MyClass<Long>(Long.class).

But are you sure you need to store the cl parameter at runtime at all? Normally you would leave it out completely, so you just write new MyClass<Long>().