Optional class ifPresent, map method

ifPresent() is given Consumer interface
ifPresentOrElse() is given Consumer interface and Runnable interface
map() is given Function interface, and Function#apply method return
map returns Optional
flatMap() is given Function interface, and Function#apply method return Optional
flatMap returns Optional

public class Outer {
    public static void main(String[] args) {
        Optional<String> o = Optional.of("abc");
        o.ifPresent((str) -> { System.out.println("optional value is " + str);});
        o.ifPresentOrElse(str -> { System.out.println("orelse optional value is " + str);},
                          () ->  { System.out.println("orelse optional value is empty");});
        System.out.println("mapping function is "+ o.<Integer>map(str -> str.length()).get());
        System.out.println("flat mapping function is "+ o.<Integer>flatMap(str -> Optional.of(str.length())).get());
        o = Optional.empty();
        o.ifPresent((str) -> { System.out.println("optional value is " + str);});
        o.ifPresentOrElse(str -> { System.out.println("orelse optional value is " + str);},
                          () ->  { System.out.println("orelse optional value is empty");});
    }
}

optional value is abc
orelse optional value is abc
mapping function is 3
flat mapping function is 3
orelse optional value is empty