Stream.findFirst different than Optional.of?

Question

Let\'s say I have two classes and two methods:

class Scratch {
    private class A{}
    private class B extends A{}

    public Optional getItems(List&         


        

Answer 1

An Optional is not a sub-class of Optional.

In the first case, you have a Stream, so findFirst returns an Optional, which cannot be converted to an Optional.

In the second case, you have a stream pipeline that returns an instance of B. When you pass that instance to Optional.of(), the compiler sees that the return type of the method is Optional, so Optional.of() returns an Optional (since an Optional can hold an instance of B as its value (since B extends A)).