Question

As per the title, can there be more than one object on the heap with the same hash code?

Answer 1

Yes.

public class MyObject {
    @Override
    public int hashCode() {
        return 42;
    }

    public static void main(String[] args) {
        MyObject obj1 = new MyObject();
        MyObject obj2 = new MyObject(); // Ta-da!
    }
}

For a less flippant answer, consider the hashCode Javadocs:

The general contract of hashCode is:

• … (snip) …
• If two objects are equal according to the equals(Object) method, then calling the hashCode method on each of the two objects must produce the same integer result.