Lambda: UnaryOperator is a Function whose input and output types match

UnaryOperator<T> is a specialization of Function<T, T> for the common case of transforming a value into another value of the same type, such as a String into a String.

Code

UnaryOperator<String> shout = s -> s.toUpperCase() + "!";
System.out.println(shout.apply("hello"));

Output

HELLO!