Java HashSet duplicates comparison

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 l开发者_运维百科ike firstName+lastName to figure out duplicates?

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.

You need to make your .equals() method return true for two Persons with the same first and last name. You need to also implement the .hashcode() method to ensure that two equal object have the same hashcode.

Your question refers to using a List, and then mentions HashSet. If preserving insertion order is important then a HashSet is not what you want, you should use LinkedHashSet.

You should just use a Set instead of a List. If you care about insertion order, use a LinkedHashSet.

Important -> You need to implement equals AND hashcode

Always implement both. And they must be consistent-> if 2 object are equals they must have the same hashcode.

THIS IS VERY IMPORTANT. READ AGAIN. :)

HashSets and HashMaps use hashcode and equals to compare elements. Diferent elements may have the same hashcode, but they are not equals