package 多态;
/**
 * 封装:坐标点相关的属性、方法代码
 * 封装成Point类
 */
public class Point {
    int x;
    int y;
    /*
     * 无参构造方法
     */
    public Point() {
    }
    /*
     * 有参构造方法
     */
    public Point(int x, int y) {
        this.x = x;
        this.y = y;
    }

    public double distance(){
        //没有同名局部变量，可以省略this
        return Math.sqrt(this.x*x+y*y);
    }
    public String toString() {
        return "("+x+","+y+")";
    }
}

package 多态;

public class Point3D extends Point{
    int z;
    public Point3D(int x,int y,int z){
        /**
         * 从父类继承的x y
         */
        this.x=x;
        this.y=y;
        this.z=z;
    }
    @Override
    public double distance() {
        return Math.sqrt(x*x+y*y+z*z);
    }
    @Override
    public String toString() {
        return "("+x+","+y+","+z+")";
    }
}

package 多态;

public class TestPoint {

    public static void main(String[] args) {
        zhuan(new Point(3,4));
        //子类对象，转型成父类型传递到zhuan方法
        zhuan(new Point3D(3,0, 4));
    }

    static void zhuan(Point p){
        System.out.println(p.toString());
        System.out.println(p.distance());
    }
}

运行结果

(3,4)
5.0
(3,0,4)
5.0