[FIXED] Filter Objects from two lists and do subtract with the attributes and store it in 3rd list in Java 8

Issue

List<Manipulate> a = new ArrayList<>();
        a.add(new Manipulate(1,100));
        a.add(new Manipulate(2,200));

        List<Manipulate> b = new ArrayList<>();
        b.add(new Manipulate(1,10));
        b.add(new Manipulate(2,20));

i have to filter these two lists by comparing the ids and subtract b(10,20) from a(100,200) and store the List of Maipulate Object to some new lists using only java 8

List<Manipulate> c = a.stream().map(k -> {
            b.stream().filter(j -> j.getId() == k.getId())
                    .forEach(i -> {
                        int i1 = k.getQuantity() - i.getQuantity();
                        k.setQuantity(i1);
                    });
            return k;
        });

Thorwing error

Required type:
List
<Manipulate>
Provided:
Stream
<Object>
no instance(s) of type variable(s) R exist so that Stream<R> conforms to List<Manipulate>

Solution

You just forgot to collect the stream back into a list.

List<Manipulate> c = a.stream().map(k -> {
            b.stream().filter(j -> j.getId() == k.getId())
                    .forEach(i -> {
                        int i1 = k.getQuantity() - i.getQuantity();
                        k.setQuantity(i1);
                    });
            return k;
        }).collect(Collectors.toList());

Answered By - Robert McKay
Answer Checked By - Terry (JavaFixing Volunteer)