Java面向对象基础之多态性,抽象类和接口

public class Animal {
 public void eat(){
 System.out.println("动物可以吃东西");
 }
}

public class Dog extends Animal{
 public void eat(){
 System.out.println("狗狗可以吃东西");
 }
}

public class Cat extends Animal{
 public void getMouse(){
 System.out.println("猫会抓老鼠");
 }
}

public class InitTest {
 public static void main(String[] args) {
 Animal obj1 = new Animal();//父类的引用指向本类对象
 Animal obj2 = new Dog();//父类的引用指向子类对象
 Animal obj3 = new Cat();
 obj1.eat();//动物可以吃东西
 obj2.eat();//20岁的狗狗可以吃东西
 obj3.eat();//动物可以吃东西
 }
}

public class InitTest {
 public static void main(String[] args) {
 Animal obj = new Dog();//向上类型转换
 if(obj instanceof Dog){
  Dog dog = (Dog)obj; //向下类型转换
 }else{
  System.out.println("不能进行Dog类型转换");
 }
 if(obj instanceof Cat){
  Cat cat = (Cat)obj;
 }else{
  System.out.println("不能进行Cat类型转换");
 }
 }
}

public abstract class Shape {
 public abstract double perimeter();
 public abstract double area();
}
public class Rectangle extends Shape {
 double length;
 double width;

 public Rectangle(double length,double width){
 this.length = length;
 this.width = width;
 }

 @Override
 public double perimeter() {
 return 2*(length+width);
 }

 @Override
 public double area() {
 return length*width;
 }

}
public class Circle extends Shape {
 double radius;
 final double PI = 3.14;

 public Circle(double radius){
 this.radius = radius;
 }

 @Override
 public double perimeter() {
 return 2*PI*radius;
 }

 @Override
 public double area() {
 return PI*radius*radius;
 }

}
这里，由于不同的形状求解周长和面积时，需要的参数个数不同，在定义抽象方法中无法统一给出参数，可以在子类中定义变量，通过初始化构造方法进行参数的传递。下面是测试方法代码：

public class ShapeTest {
 public static void main(String[] args) {
 Shape s1 = new Rectangle(2,4);
 Shape s2 = new Circle(3.9);
 System.out.println("矩形的周长："+s1.perimeter());
 System.out.println("矩形的面积："+s1.area());
 System.out.println("圆形的周长："+s2.perimeter());
 System.out.println("圆形的面积："+s2.area());
 }
}

public interface IPlayGame {
 public void playGame();
}
public class SmartPhone extends Telphone implements IPlayGame{

 @Override
 public void call() {
 System.out.println("SmartPhone可以打电话");
 }

 @Override
 public void message() {
 System.out.println("SmartPhone可以发短信");
 }

 @Override
 public void playGame() {
 System.out.println("玩游戏的功能");
 }

}
public class PSP implements IPlayGame{
 @Override
 public void playGame() {
 System.out.println("玩游戏的功能");
 }
}
public class InterfaceTest {

 public static void main(String[] args) {
 IPlayGame ip1 = new SmartPhone();
 IPlayGame ip2 = new PSP();
 ip1.playGame();
 ip2.playGame();
 }

}

 public static void main(String[] args) {
 IPlayGame ip3 = new IPlayGame(){
 @Override
 public void playGame() {
  System.out.println("使用匿名内部类的方式实现接口");
 }
 };
 ip3.playGame();
}