Why doesn't Java 8's Predicate extend Function

Question

If I wrote the Predicate interface, I\'d want to encode in the interface the fact that it\'s just a function that returns a primitive boolean, like thi

Answer 1

The method in Predicate returns boolean. The method in Function returns Boolean. They are not the same. Although there is autoboxing, Java methods don't use wrapper classes when primitives would do. Also, there are differences like Boolean can be null while boolean can't.

It's even more different in the case of Consumer. The method in Consumer has return type void, which means it can implicitly return or return using return;, but the method in Function must return using return null; explicitly.