How does method reference casting work?

Question

public class Main {
    interface Capitalizer {
        public String capitalize(String name);
    }

    public String toUpperCase() {
        return \"ALLCAPS\";
          


        

Answer 1

You have a method which

public String capitalize(String name);

Takes a String and returns a String. Such a method can have a number of patterns.

A constructor

c = String::new; // calls new String(String)
// or
c = s -> new String(s);

A function on String which takes no arguments

c = String::toLowerCase; // instance method String::toLowerCase()
// or
c = s -> s.toLowerCase();

of a method which takes a String as the only argument

// method which takes a String, but not a Main
public static String toUpperCase(String str) { 

c = Main::toUpperCase;
// or
c = s -> toUpperCase(s);

In every case, the method referenced has to take the String.

If not you can do this instead.

c = s -> capitalize(); // assuming Main.capitalize() is static

This tells the compiler to ignore the input.