JAVA--多态及向上、向下转型问题
public class Polymorphic {public static void main(String [] args){//多态-----动态绑定(后期绑定)//程序运行时根据具体参数地址找到内存对象 从而能够正确执行对应的方法。ShapeController objShapeController = new ShapeController();Shape objShape = new Circle();objShapeController.doActive(objShape); // 结果:Circle.draw Circle.moveobjShape = new Square();objShapeController.doActive(objShape); // 结果:Square.draw Square.move//向上转型:安全的 但可能会丢失子类数据Shape objShape11 = new Circle();//向上转型objShape11.draw();//结果:Circle.draw . objShape11引用指向 new Circle()的地址。//objShape11.ping(); //此方法掉不通。----方法丢失//向下转型:不安全 必须知道确切的类型 并且执行过程中是程序效率降低(执行类型检查)Shape objShape22 = new Circle();//向上转型((Circle)objShape22).ping();//向下转型。 必须知道具体的子类类型 执行强制转换objShape22 = new Square();//((Circle)objShape22).ping();//结果：ClassCastException//((Circle)objShape22).draw();//结果：ClassCastException}}class ShapeController{void doActive(Shape objShape){objShape.draw();objShape.move();}}class Shape{void draw (){};void move (){};} class Circle extends Shape{@Overridevoid draw() {System.out.println("Circle.draw");}@Overridevoid move() {System.out.println("Circle.move");}void ping(){System.out.println("Circle.ping");}}class Square extends Shape{@Overridevoid draw() {System.out.println("Square.draw");}@Overridevoid move() {System.out.println("Square.move");}void tt(){System.out.println("Square.tt");}}?