Refactor for-loop with side effects to stream

Question

I want to refactor a Java 7 code to Java 8.

Here the Java 7 code:

List<A> aList = new ArrayList<>();
for (B b : bList) {
    D d = new D(b.getSomeWhat());
    d.setDisabled(true);
    aList.add(d);
}

I try this one in Java 8:

bList.stream().map(b -> {
    D d = new new D(b.getSomeWhat());
    d.setDisabled(true);
}).collect(Collectors.toList());

I have a missisng return statement error.

How can I write the code with Java 8 streams?

Answer 1

Return d in your mapping:

bList.stream().map(b -> {
    D d = new D(b.getSomeWhat());
    d.setDisabled(true);
    return d;
}).collect(Collectors.toList());

Answer 2

There are two problems in your code:

1. using () - {} construct requires return statement,
2. d.setDisabled(true) returns void.

You could do something like this:

    bList.stream()
        .map(B::getSomeWhat)
        .map(D::new)
        .map(d -> {
            d.setDisabled(true);
            return d;
    }).collect(Collectors.toList());