Advanced Concepts

filter is another usefull function to select elements from a collection having a particular property (aka. predicate):

  public static void main(String[] args) {
    List<Integer> xs,ys,zs;
    xs = Arrays.asList(-1,-2,-1,0,1);
    ys = xs.stream().filter(x->(x%2)==0).toList();
    zs = xs.stream().filter(x->!ys.contains(x)).toList(); // (*)
    System.out.println(zs);
  }

What are the values of ys and zs ? What set's operation is performed by (*) ?