有意思的问题

public class Test
{
    public void changeApple(Apple a)
    {
        Apple a2 = new Apple();
        a2.color = "red";
        a = a2;
    }
    public void changeApple2(Apple a)
    {
        a.color = "red";
    }
    public static void main(String[] args)
    {
        Apple a = new Apple();
        a.color="blue";
        new Test().changeApple(a);
        System.out.println(a.color);
        new Test().changeApple2(a);
        System.out.println(a.color);
    }
}
class Apple
{
    public String color;
}

//输出结果:blue
             red