Java谓词与嵌套对象的链接

Question

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;

Answer 1

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);