Java难点，函数参数传递引用传递，值传递的理解

package com.day1204;

public class MethodTest01 {
    public static void main(String[] args) {
        int x = 10;
        add(x);
        System.out.println("main:\t"+x);
    }

    public static void add(int x) {
        x++;
        System.out.println("add:\t" + x);
    }
}

package com.day1205;
public class MethodTest02 {
    public static void main(String[] args) {
        Person p = new Person();
        p.age = 10;
        add(p);
        System.out.println("main:\t"+p.age);
    }
    public static void add(Person p) {
        p.age++;
        System.out.println("add:\t"+p.age);
    }
}
class Person {
    int age;
}