Question

I have a class Person which contains String firstName, lastName. I want to insert instances of this class into a List, but I don’t want to insert duplicates.

How do I use a HashSet such that it uses something like firstName+lastName to figure out duplicates?

Answer 1

You need an equals() and a hashCode() method in your Person class.

equals() is straightforward, and for hashCode() the easiest solution is:

public int hashCode() {
  return Arrays.hashCode( new Object[] { firstName, lastName } );
}

Although if your Person object is immutable (as it should be, if you’re putting it in a HashSet), you should cache this value.