import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;

public class test {
    public static void main(String[] args) throws NoSuchMethodException, InvocationTargetException, IllegalAccessException, InstantiationException {
        System.out.println("Hello World!");
        Class<User> clas = User.class;
        Method m = clas.getMethod("method", String.class);
        m.invoke(null, "aa");//静态方法可省略对象，直接用null替代，或用clas

        m = clas.getDeclaredMethod("method", int.class);//非public方法要用declared获取
        m.setAccessible(true);//非public方法需要设置为可访问
        m.invoke(clas.newInstance(), 1);//非静态方法需要提供底层的类对象
    }
}

class User {
    public static void method(String s) {
        System.out.println(s);
    }

    private void method(int i) {
        System.out.println(i);
    }
}

不同元类的方式

import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;

public class test {
    public static void main(String[] args) throws NoSuchMethodException, InvocationTargetException, IllegalAccessException, InstantiationException {
        System.out.println("Hello World!");
        User us = new User();
        Method m = us.getClass().getMethod("method", String.class);
        m.invoke(us, "aa");//静态方法可省略对象，直接用null替代，或用clas
        m = us.getClass().getDeclaredMethod("method", int.class);
        m.setAccessible(true);//非public方法需要设置为可访问
        m.invoke(us, 1);//非静态方法需要提供底层的类对象

    }
}

class User {
    public static void method(String s) {
        System.out.println(s);
    }

    private void method(int i) {
        System.out.println(i);
    }
}