Java 8: modify specific element in the stream by using lambda expressions

Question

I need to modify a list on int as it follows:

• Every element == 10 needs to be doubled

Here is my attempt:

list.stream()
            .filter(val -> val.getValue() == 10)
            .map(val -> {
                val.doubleValue();
                return val;
            })
            .forEach(System.out::println);

The problem is that I'm filtering the elements, while I would like to keep them all and just modify the ones == 0.

EDIT: the list is composed of elements of MyType, defined as it follows:

public class MyType {

    private int val;

    public MyType(int v){
        this.val = v;
    }

    public void doubleVal(){
        val*val;
    }

    public int getValue(){
        return val;
    }
}

Any suggestion?

Answer 1

Don't use filter. Put all the logic in map :

list.stream()
    .map(val -> val == 10 ? 2*val : val)
    .forEach(System.out::println);

EDIT : I simplified the code after your clarification that the elements of the list are Integers. Note that the original List remains unchanged.

Answer 2

Assuming that your list is a list of Val, and Val is something like

class Val {
  private int v;

  public Val(int v) {
    this.v = v;
  }
  int getValue() {
    return v;
  }

  public void doubleValue() {
    v *= 2;
  }
}

then

  public static void main(String ... args ) {
        List<Val> ints = Arrays.asList(new Val(1), new Val(5), new Val(10), new Val(2));
        ints.stream().map((v) -> {
            if (v.getValue() == 10) v.doubleValue(); return v;
        }).forEach(v -> System.out.println(v.getValue()));

    }

will do the trick.