在列表上迭代一次，但返回两个列表

Question

I have a List<Foo> : foos . And I have two methods that return Bar : Bar doThingOne(Foo foo) and Bar doThingTwo(Foo foo) . I want to end up with two List<Bar> s – one by iterating over foos and applying doThingOne() to each Foo , and the other by doing the same thing but with doThingTwo() . Is it possible to do this without iterating over foos twice?

Answer 1

Isn't it what you want? It's so simple that I have some doubt.

List<Bar> lb1 = new ArrayList<Bar>();
List<Bar> lb2 = new ArrayList<Bar>();
for (Foo f : foos) {
    lb1.add(doThingOne(f));
    lb2.add(doThingTwo(f));
}

Answer 2

You can do this with stream :

List<Bar> barList1 = new ArrayList<>();
List<Bar> barList2 = fooList.stream().peek(f -> barList1.add(doThingOne(f))
    .map(f -> doThingTwo(f)).collect(Collectors.toList());