Java 8 stream – merge two sets to make them unique in a specific field [copy]

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This is the best I can do in Java, but it collects unique names instead of dogs: (dogs contain fields other than names)

// collect all dogs names from first list
List<String> dogNames1 = dogsList1.stream()
     .map(x -> x.getName()).collect(Collectors.toList()); 

dogList2.stream()
     .filter(x->!dogNames1.contains(x.getName()))
     .forEach( x->
            dogsList1.add(x);
     );

Can it be improved? There are other better solutions or optimization methods

Solution

You can use to merge multiple streams and delete duplicates

For the first dog with a given name, you can do it

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.stream.Collectors;
import java.util.stream.Stream;

public class A {

    public static void main(String[] args) {
        List<Dog> dogList1 = Arrays.asList(new Dog("a",1),new Dog("b",2),new Dog("f",3));
        List<Dog> dogList2 = Arrays.asList(new Dog("b",4),new Dog("c",5),6));
        List<Dog> dogList3 = Arrays.asList(new Dog("b",7),new Dog("d",8),new Dog("e",9));
        List<Dog> dogs = new ArrayList<>(
                Stream.of(dogList1,dogList2,dogList3)
                        .flatMap(List::stream)
                        .collect(Collectors.toMap(Dog::getName,d -> d,(Dog x,Dog y) -> x == null ? y : x))
                        .values());
        dogs.forEach(System.out::println);
    }
}

class Dog {
    String name;
    int id;

    public Dog(String name,int id) {
        this.name = name;
        this.id = id;
    }

    public String getName() {
        return name;
    }

    @Override
    public String toString() {
        return "Dog{" +
                "name='" + name + '\'' +
                ",id=" + id +
                '}';
    }
}

print

Dog{name='a',id=1}
Dog{name='b',id=2}
Dog{name='c',id=5}
Dog{name='d',id=8}
Dog{name='e',id=9}
Dog{name='f',id=3}

In each case, you can see the first instance of the reserved name

For unique names

Set<String> names = Stream.of(dogList1,dogList3)
                          .flatMap(List::stream)
                          .map(Dog::getName)
                          .collect(Collectors.toSet());