java - Stream foreach Java 8 中的递增计数器

Question

我想在使用 foreach 循环时增加一个 counter，它是一个 AtomicInteger

public class ConstructorTest {

public static void main(String[] args) {
    AtomicInteger counter = new AtomicInteger(0);
    List<Foo> fooList = Collections.synchronizedList(new ArrayList<Foo>());
    List<String> userList = Collections.synchronizedList(new ArrayList<String>());
    userList.add("username1_id1");
    userList.add("username2_id2");

    userList.stream().map(user -> new Foo(getName(user), getId(user))).forEach(fooList::add);
    //how do I increment the counter in the above loop

    fooList.forEach(user -> System.out.println(user.getName() + "   " + user.getId()));
}

private static String getName(String user) {
    return user.split("_")[0];
}

private static String getId(String user) {
    return user.split("_")[1];
}
}

Answer 1

取决于你想增加的地方。

要么

userList.stream()
        .map(user -> {
               counter.getAndIncrement();
               return new Foo(getName(user), getId(user));
            })
        .forEach(fooList::add);

或

userList.stream()
        .map(user -> new Foo(getName(user), getId(user)))
        .forEach(foo -> {
            fooList.add(foo);
            counter.getAndIncrement();
        });