// functional/UnboundMethodReference.java

// (c)2020 MindView LLC: see Copyright.txt

// We make no guarantees that this code is fit for any purpose.

// Visit http://OnJava8.com for more book information.

// Method reference without an object

interface MakeString {

String make();

}

class X {

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

}

interface MakeString2 {

String make();

}

class X2 {

String f() {

System.err.println("success!");

return "success!";

}

}

interface TransformX {

String transform(X x);

}

public class UnboundMethodReference {

public static void main(String[] args) {

X2 x2 = new X2();

// MakeString2 c = X2::f; 没有实例

MakeString2 c = x2::f;

c.make();

// MakeString ms = X::f; // [1] self-note: 这个是大写的X,不是上面例子的小写d了,没有实例,因此其实需要一个实例用作参数.

TransformX sp = X::f; //总之静态方法引用 X::f 写法是需要多一个参数，要么就用非静态的方法引用 x2::f

X x3 = new X();

System.err.println(sp.transform(x3)); // [2]

System.err.println(x3.f()); // Same effect

}

}

/* Output:

X::f()

X::f()

*/