public class RefDemo {
    public static void main(String[] args) {
        Person person1 = new Person();
        PersonPack personPack = new PersonPack();
        personPack.person = person1;

        // 打印person
        System.out.println(personPack.person);

        change(personPack);

        // 再打印person
        System.out.println(personPack.person);
    }

    public static void change(PersonPack personPack) {
        Person person2 = new Person();
        personPack.person = person2;
    }
}

/**
 * Person类
 */
class Person {

}

/**
 * 包装类：PersonPack
 */
class PersonPack {
    public Person person;
}