java的值传递还是引用传递

public class Stu {private int age = 10;public static void doMethod(Stu a,Stu b){a.age = 20;b = a;b.age = 30;}public static void main(String[] args) {Stu stu = new Stu();Stu stu2 = new Stu();stu.age  = 40;doMethod(stu,stu2);System.out.println(stu.age);System.out.println(stu2.age);}}猜猜输出结果是什么？哈哈