OnJava8-Examples/functional/UnboundMethodReference.java

// functional/UnboundMethodReference.java
// (c)2016 MindView LLC: see Copyright.txt
// We make no guarantees that this code is fit for any purpose.
// Visit http://mindviewinc.com/Books/OnJava/ for more book information.
// Method reference without an object

class X {
  String f() { return "X::f()"; }
}

interface MakeString {
  String make();
}

interface TransformX {
  String transform(X x);
}

public class UnboundMethodReference {
  public static void main(String[] args) {
    // MakeString ms = X::f; // (1)
    TransformX sp = X::f;
    X x = new X();
    System.out.println(sp.transform(x)); // (2)
    System.out.println(x.f()); // Same effect
  }
}
/* Output:
X::f()
X::f()
*/