[Day23] CH11：刘姥姥逛物件导向的世界——多型

今天要来接续昨天没介绍完的物件导向的第三个特性——多型。

多型（Polymorphism）

父类别可透过子类别衍伸成多种型态，而父类别为子类别的通用型态，再透过子类别可覆写父类别的方法来达到多型的效果，也就是同样的方法名称会有多种行为。由昨天的范例来看：

public class Zoo2{
    public static void main(String[] args){
        Animal s1 = new Sheep("绵羊1号","黑色");
        Animal s2 = new Sheep();
        s2.setName("绵羊2号");
        //s2.setWoolColor("白色"); 错误
        System.out.println(s1.getName() + s1.move(10)); //s1.getWoolColor() 错误
        System.out.println(s2.getName() + s2.move(5));   //s2.getWoolColor() 错误
    }
}

class Animal{
    private String name;
    
    public Animal(){

    } 
    
    public Animal(String name){
        this.name = name;
    }

    public String move(int units){
        return "移动" + units + "步";
    }

    public String getName(){
        return name;
    }

    public void setName(String name){
        this.name = name;
    }
}

class Sheep extends Animal{
    private String woolColor;

    public Sheep(){
        super();
    }

    public Sheep(String name, String woolColor){
        super(name);
        this.woolColor = woolColor;
    }

    public void setWoolColor(String woolColor){
        this.woolColor = woolColor;
    }

    public String getWoolColor(){
        return woolColor;
    }

    @Override
    public String move(int units){
        return "跑" + units + "步";
    }
}