How to move to the next value in a loop when using Java 8 Stream API

Question

When using external iteration over an java collectios we use keyword "continue" for move to the next value in a loop. What about in the case, when we use java stream API? Example:

List<User> users;

for(Item item : item){
    users.stream()
        .filter(user -> user.getName().equals("Tom"))
        .findFirst()
        .ifPresent(move to the next value in a outer loop(items) ???? like **continue**;);

    more code here...
}

Without stream:

 for(Item item : item){
    for(User user : users){
     if(user.getName("Tom") exist = true;
    }
  if (exist) continue;

    more code here...
}

What you want to do exactly? What you want to do after you find any match ? — Youcef LAIDANI
– Youcef LAIDANI, Commented Jun 5, 2018 at 13:33
findFirst() returns just a single element (if present). If you want to iterate over all the elements, use forEach(). — Eran
– Eran, Commented Jun 5, 2018 at 13:33
I want to skip itteration, if user.getName().equals("Tom"), only one itteration, and move to next item — FranzF
– FranzF, Commented Jun 5, 2018 at 13:37

Pratik soni · Accepted Answer · 2018-06-05 13:46:21Z

2

Java stream api is used only to work on that particular stream of elements. You can never use it for control statements like ‘break’ or ‘continue’ to control external loops (like here you want to control ‘Item’ loop).

answered Jun 5, 2018 at 13:46

Pratik soni

1081 gold badge3 silver badges13 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Bohemian · Accepted Answer · 2018-06-05 13:57:23Z

2

Maybe you just want:

for (Item item : item){
    if (users.stream().anyMatch(u -> u.getName().equals("Tom"))) {
        continue;
    }

    // more code here...
}

answered Jun 5, 2018 at 13:57

Bohemian♦

427k103 gold badges603 silver badges750 bronze badges

3 Comments

Nikolas Over a year ago

I'd firstly evaluate the condition and then enter the loop.

Bohemian Over a year ago

@Nikolas except "more code here" might add Tom to users.

Nikolas Over a year ago

@Boheamian: A very good point! :)) +1.. It depends that "more code here" really does.

Nikolas · Accepted Answer · 2018-06-05 17:04:48Z

The Stream-API doesn't provide the iteration mechanism like the Iterator does, for this you have to use the Iterator<User>. However, it's good to filter the correct values first.

List<User> filteredUsers = users.stream()
    .filter(user -> user.getName().equals("Tom"))
    .collect(Collectors.toList());

Now get an Iterator<User> and iterate through.

Iterator<User> iterator = filteredUsers.iterator();
while (iterator.hasNext()) {
    User user = iterator.next()
    // Take a control over the further iteration here...
}

Edit:

According to your edit, you want to find out if any User has a name Tom, then perform the iteration over the items. Use the anyMatch(Predicate<? super T> predicate) method which returns true if any element of the stream matches the predicate. It accepts the same predicate as the filter(Predicate<? super T> predicate) does.

if (users.stream().anyMatch(user -> user.getName().equals("Tom"))) {
    for (Item item : item) {
        // ...
    }
}

Edit2: As @Bohemian has correctly noted, consider checking the presence of the element with each iteration since there may be an element with "Tom" added and the condition no longer remains false.

Collectives™ on Stack Overflow

How to move to the next value in a loop when using Java 8 Stream API

3 Answers 3

Comments

3 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

Comments

3 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related