Java 8 Distinct by property

Question

In Java 8 how can I filter a collection using the Stream API by checking the distinctness of a property of each object?

For example I have a list of

Answer 1

You can wrap the person objects into another class, that only compares the names of the persons. Afterward, you unwrap the wrapped objects to get a person stream again. The stream operations might look as follows:

persons.stream()
    .map(Wrapper::new)
    .distinct()
    .map(Wrapper::unwrap)
    ...;

The class Wrapper might look as follows:

class Wrapper {
    private final Person person;
    public Wrapper(Person person) {
        this.person = person;
    }
    public Person unwrap() {
        return person;
    }
    public boolean equals(Object other) {
        if (other instanceof Wrapper) {
            return ((Wrapper) other).person.getName().equals(person.getName());
        } else {
            return false;
        }
    }
    public int hashCode() {
        return person.getName().hashCode();
    }
}