java - How to add two stream elements together?

Question

I am new to streams and collections.I have a class foo with a name and number of balls which each person has. I have this as a list of foo objects.I would like to search if two foo objects have the same name and add their balls together and give of names back based on the lowest no of balls. So I know how to do this with loops.How is this possible to do with streams? Thank you

Answer 1

This might work for you:

import java.util.*;
import java.util.function.Function;
import java.util.stream.Collectors;


class Foo {
    String name;
    Integer noOfBalls;

    public Foo(String name, Integer noOfBalls) {
        this.name = name;
        this.noOfBalls = noOfBalls;
    }

    public String getName() {
        return name;
    }

    public Integer getNoOfBalls() {
        return noOfBalls;
    }

    @Override
    public String toString() {
        return "Foo{" +
                "name='" + name + ''' +
                ", noOfBalls=" + noOfBalls +
                '}';
    }
}
public class Test {

    public static void main(String[] args){
        ArrayList<Foo> arrayList = new ArrayList<>();
        arrayList.add(new Foo("John",10));
        arrayList.add(new Foo("Babu",1));
        arrayList.add(new Foo("Alex",5));
        arrayList.add(new Foo("Babu",5));
        arrayList.add(new Foo("John",10));
        ArrayList<Foo> arrayListTemp = arrayList.stream()
                .collect(Collectors.collectingAndThen(Collectors.toMap(Foo::getName, Function.identity(), (left, right) -> {
                    left.noOfBalls= left.noOfBalls + right.noOfBalls;
                    return left;
                }), m -> new ArrayList<>(m.values())));
        arrayListTemp.sort(Comparator.comparingInt(Foo::getNoOfBalls));
        arrayListTemp.forEach(System.out::println);

    }

}

Here I am converting list to map(key as name and value as Foo object) and if the name already exists then merging Foo object by adding noOfBalls.