1.参数传递的统一是值
2.构造方法

 public class ParamTest
{
     public void changePoint(Point point)
 {
        point = new Point();

    point.x = 3;
            point.y = 4;

 } 

 public static void main(String[] args)
 {
        ParamTest pt = new ParamTest();
    Point point = new Point();

    pt.changePoint(point);

    System.out.println(point.x);
    System.out.println(point.y);

 }
}

class Point
{
    int x;//横坐标
int y;//纵坐标
}