Remove from ArrayList if one value of objects repeats

Question

How to remove duplicate object from ArrayList, but only if one specific value from object repeats with another object?

For example: I have class named Person with fields:

private String city;
private String firstName;
private String lastName;
private Long magicNumber;

I want to remove "older" Person with same "magicNumber" as the new One and keep him in ArrayList.

Answer 1

Using streams :

Collection<Person> filterd = persons.stream()
            .collect(Collectors.toMap(
                    Person::getMagicNumber, p -> p, (p1, p2) -> p2))
            .values();

Answer 2

Well, assuming you have overriden public boolean equals(Object object) in your class in order to compare your magicNumber field:

https://docs.oracle.com/javase/7/docs/api/java/lang/Object.html#equals(java.lang.Object)

List<Person> persons = new ArrayList<>();
public void addToList(Person person) {
     if(persons.contains(person)) {
         persons.set(persons.indexOf(person), person);
     } else {
         persons.add(person);
     }

}

Answer 3

public void addPerson(Person p) {
    list.removeIf(o -> o.magicNumber.equals(p.magicNumber));
    list.add(p);
}