Question

I’m overriding the equals(Object o) method of an Object that is identified by an string:

class User {
@Override
public boolean equals(Object o) {       
    return o != null && o.hashCode() == this.hashCode();
}

@Override
public int hashCode() {
    return id.hashCode();
}
}

But I’d like to check also if o is a subclass of this or vice versa before returning true in the method equals()

for the first case I can use if (o instance of User) but how can I make the check in the other way?

Thanks

Edit: Since I’ve not explained it correctly I’m going to explain the complete problem:

I have the class

public abstract class UniqueIdentifiedObject<E> {
    private E id;

    protected UniqueIdentifiedObject(E id) {
        super();
        this.id = id;
    }

    public E getId() {
        return id;
    }

    @Override
    public boolean equals(Object o) {
        return o != null && o.hashCode() == this.hashCode();
    }

    @Override
    public int hashCode() {
        return id.hashCode();
    }

}

and the idea is to inherit this class with an object when it is unique identified by a element: For example if the Users of my app are identified by a integer i’ll use:

class User extends UniqueIdentifiedObject<Integer>

and for the Movies

class Movie extends UniqueIdentifiedObject<Integer>

The problem with this implementation of UniqueIdentifiedObject is that if call equals() with the movie with id = 1 and the user with the id=1 it will return true.

How can I solve this?

Answer 1

this.getClass().isAssignableFrom(o.getClass());

Class.isAssignableFrom

From the javadoc:

Determines if the class or interface represented by this Class object is either the same as, or is a superclass or superinterface of, the class or interface represented by the specified Class parameter. It returns true if so; otherwise it returns false. If this Class object represents a primitive type, this method returns true if the specified Class parameter is exactly this Class object; otherwise it returns false.

So the above checks that the class returned by this is a superclass of the class returned be o.