How can I convert my java code containing simple for loop using stream and lambda?

Question

I'm trying to convert old-style for loop with some newly generated variables and if statements int the new style using java streams and lambda expression.

    for (MyClass a : list_1) {
      if (a.myMethod() != null) {
        List<Integer> list_2 = myMap.get(/*some code*/);                 
        if (list_2 == null) {
          list_2 = new ArrayList<>();
          myMap.put(/*some code*/);
        }
        list_2.add(/*some code*/);
      }
    }

Christian · Accepted Answer · 2019-07-12 11:15:20Z

2

Let's take a closer look to the different parts.

First you need a stream:

list_1.stream()

Next you have an if. This can most of the time be converted into filter:

.filter(a -> a.myMethod() != null)

Then, you want to do some things with your data. you can use forEach for that:

list_1.stream()
  .filter(a -> a.myMethod() != null)
  .forEach(a -> {
    // only put list in if absent
    myMap.putIfAbsent(/* your stuff */);
    myMap.get(/* some code */).add(/* your stuff */);
  });

answered Jul 12, 2019 at 11:15

Christian

22.4k11 gold badges84 silver badges107 bronze badges

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

2 Comments

Devender Kumar Over a year ago

Where should I create list_2 ? @christian-wörz

Christian Over a year ago

Where you need it. I think you just put it inside your map and then get it from your map.

Collectives™ on Stack Overflow

How can I convert my java code containing simple for loop using stream and lambda?

1 Answer 1

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related