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javajava-8predicatechaining

Java predicate chaining with nested object

private static final Predicate<Parent> HAS_SON = parent -> IS_CHILD(parent.getChild);
private static final Predicate<Child> IS_CHILD = Objects::nonNull;
private static final Predicate<Parent> IS_PARENT = Objects::nonNull;
private static final Predicate<Parent> IS_FATHER = IS_PARENT.and(HAS_SON);

I am trying to chain predicates, with one twist, and that is at one of predicate I want to use child object.

This is hypothetical situation I tried to make things easier for understanding.

  1. Call will be made to is_father (parent)
  2. is_father will check if parent is not null
  3. and() has_son
  4. has_son will call is_child (parent.getChild())
  5. is_child will check if child is not null

There is a problem HAS_SON, I know syntax is not right, and may be nesting(parent.child) might not be allowed. Can some one please confirm? right now work around I am using is 

private static final Predicate<Parent> HAS_SON = parent -> parent.getChild() != null;
Solution

  • Do not forget that a Predicate is triggered by using the test method of the FunctionalInterface. The following will work

    private static final Predicate<Child> IS_CHILD = Objects::nonNull;
private static final Predicate<Parent> HAS_SON = parent -> IS_CHILD.test(parent.getChild);
private static final Predicate<Parent> IS_PARENT = Objects::nonNull;
private static final Predicate<Parent> IS_FATHER = IS_PARENT.and(HAS_SON);