值传递和引用传递

public class Test {
    public static void main(String[] args) {
        UserA u = new UserA("AAA", 1);
        Test t = new Test();
        System.out.println("初始 ： " + u);
        t.test(u);
        System.out.println("最终 ： " + u);

    }
    public void test(UserA userA) {
        System.out.println("入参 userA : " + userA);
        userA.setName("ooooo");
        userA = new UserA("xxxxxxxxxxx", 99);
        System.out.println("出参 userA : " + userA);
    }
}

class UserA {
    private String name;
    private int age;

    public UserA() {
    }

    public UserA(String name, int age) {
        this.name = name;
        this.age = age;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    @Override
    public String toString() {
        return "UserA[name=" + name + ", age = " + age + "]";
    }
}

执行结果：
初始 ： UserA[name=AAA, age = 1]
入参 userA : UserA[name=AAA, age = 1]
出参 userA : UserA[name=xxxxxxxxxxx, age = 99]
最终 ： UserA[name=ooooo, age = 1]