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77 lines
1.3 KiB
77 lines
1.3 KiB
public class Jb31_ObjPol
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{
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//对象的多态性;代码中的体现就是父类或接口的引用指向其子类的对象
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public static void main(String[] args)
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{
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/*自动类型提升(向上转型)，猫对象提升为动物类型.但特有功能无法访问
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作用是限制对特有功能的访问*/
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Animal a = new Cat();
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a.eat();
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//如果仍要使用猫的特用功能，可将对象向下转型
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//自始至终都是子类对象进行类型的变换
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Cat c = (Cat)a; //向下转型目的是为了使用子类的特用方法
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c.eat();
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c.catch();
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/*
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Cat c = new Cat();
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//Dog d = new Dog();
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//c.eat();
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method(c);
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method(new Dog());
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*/
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method(new Cat());
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}
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/*多态好处：提高代码的扩展性，前面定义的代码可使用后期的内容
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弊端：前期定义的内容不能使用（调用）后期子类的特有内容
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使用多态前提：必须有关系、继承、实现
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要有方法覆盖
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*/
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public static void method(Animal a)
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{
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a.eat();
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if (a instanceof Cat)
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//instanceof 用于判断对象的具体类型，只能用于引用数据类型判断
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//通常在向下转型前用于健壮性的判断
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{
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Cat c2 = (Cat)a;
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c2.catch();
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}
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else if (a instanceof Dog)
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{
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Dog d2 = (Dog)a;
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d2.watchHome();
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}
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}
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}
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abstract class Animal
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{
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abstract void eat();
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}
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class Dog extends Animal
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{
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public void eat()
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{
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System.out.println("吃屎");
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}
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public void watchHome()
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{
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System.out.println("看家");
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}
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}
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class Cat extends Animal
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{
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public void eat()
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{
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System.out.println("吃鱼");
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}
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public void catch()
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{
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System.out.println("捉老鼠");
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}
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}
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