Java hashCode from one field

Question

Edit: Prepare my objects for the use within a HashMap.

after reading a bit about how to generate a hash code, im kind of confused now. My (probably trivial) question

Answer 1

If you want objects with different ids to identified by that id all you need to do is return it/compare it.

private final int id;

public int hashCode() { return id; }

public boolean equals(Object o) { 
    return o instanceof ThisClass && id == ((ThisClass)o).id;
}