Java Stream, Need to update list of list objects

March 27, 2024

Test.java

  
  private String Names;
  private List<InnerList> innerlist = new ArrayList<InnerList>();

InnertList.java

  private String id;
  private Long x;
  private Long y;

[class Test {
    Name: test
    innerlist: [class Innerlist{
        id: 1
        x: 0
        y: 0
    }]
}]

I have following list:
List\<Test\> list = new ArrayList\<Test\>();

Now, I need to update x or y based on two conditions: if Name matches to "Test" & id matches to 1.

I tried writing, but I’m not sure how to update the x/y using setter. I need filter it twice but not sure how to put a condition when getInnerList because the condition is on the variable of inner list.

list.stream().filter(u-\>u.getName().equals("Test")).filter(t1-\>t1.getInnerList());

>Solution :

The part .filter(t1->t1.getInnerList()) doesn’t really make sense, since .filter(...) expects a predicate as the argument, i.e. a lambda with boolean as the return value. I’m not 100% sure about what you want to achieve, but I assume this would solve your case:

list.stream()
  .filter(u -> "Test".equals(u.getName()))
  .flatMap(u -> u.getInnerList().stream())
  .filter(i -> i.getId() == 1)
  .forEach(i -> {
    // write your setters on `i` here
  }
)

Using Stream::flatMap here, we obtain a stream of the elements of innerList for the list elements which satisfies the previous filter.