Overriding "equals" method: how to figure out the type of the parameter?

Question

I'm trying to override equals method for a parameterized class.

@Override
public boolean equals(Object obj) {
    if (this == obj)
        return true;
    if (obj == null)
        return false;
    if (!(obj instanceof Tuple))
        return false;

    Tuple<E> other = (Tuple<E>) obj; //unchecked cast
    if (!a0.equals(other.a0) && !a0.equals(other.a1)) {
        return false;
    }
    if (!a1.equals(other.a1) && !a1.equals(other.a0)) {
        return false;
    }

    return true;
}

How can I make sure that <E> of the other object is the same as this?

Answer 1

You can do it by retaining a reference to Class<E> type. However, in my opinion, equality tests should be about the values the objects represent rather than the concrete types the values get expressed.

A classic example of this is the Collections API for example. new ArrayList<String>().equals(new LinkedList<Object>()) returns true. While these have completely different types, they represent the same value, namely "an empty collection".

Personally, should two Tuples that represent the same data (e.g. ("a", "b")) be not equal, because one is of type Tuple<String> while the other is Tuple<Object>?