Java calls private methods of classes from outside

Considering that we have such a strange class: [java] package org. tsw; public class SecretTool {private SecretTool () {} private void myMotto () {System. out. println ("I like potato");} private int calculate (int left, int right) {return left + right;} There are two strange points: the first, this class displays the declaration of a private constructor (the compiler will not automatically add the default no-argument constructor). Normally, we cannot get an instance of it, even if we get an instance of it, we cannot use it either, because both of its methods are private. How can we call it? Reflection [java] public static void main (String [] args) throws Exception {Constructor <?> Constructor = SecretTool. class. getDeclaredConstructors () [0]; constructor. setAccessible (true); SecretTool tool = (SecretTool) constructor. newInstance (); // obtain an instance of the instance for (Method method: SecretTool. class. getDeclaredMethods () {method. setAccessible (true); if (method. getName (). equals ("mymoals") {method. invoke (tool); // call a private method without return values and parameters} else if (method. getName (). equals ("calculate") {Integer result = (Integer) method. invoke (tool, 1, 2); System. out. println ("1 + 2 =" + result. toString (); // The returned value of the call is an integer and the private method with the parameter }}} output: [plain] I like potato 1 + 2 = 3