java中对象转换

java的变量类型之间可以进行转换，对象之间也可以。

子类对象转为父类对象，可以不进行强制转换，因为子类继承父类对象。
但是，当父类对象转换为子类对象时（当且仅当父类对象本来是由子类默认转换过去的情况），可以对父类对象进行强制转换。

public class TestObject {
    public static void main(String[] args) {
        // TODO Auto-generated method stub

        Animal a = new Animal();
        Dog d = new Dog("yellow");
        d.name = "bigYellow";
        System.out.println( a.print( d ) );    
    }
}

class Animal{
    String name;
    
    public void setName(String n){
        this.name = n;
    }
    
    public String getName(){
        return this.name;
    }
    
    public String print(Animal a){
        String result = "";
        if (a instanceof Dog) {
            Dog d = (Dog)a;
            result = "Name:" + a.name + "\n" + "FurColor:" + d.furColor;
        }else if (a instanceof Cat) {
            Cat c = (Cat)a;
            result = "Name:" + a.name + "\n" + "EyeColor:" + c.eyeColor;
        }else{
            result = "Name:" + a.name;
        }
        return result;    
    }
}

class Cat extends Animal{
    String eyeColor;
    public void setEyeColor(String e){
        this.eyeColor = e;
    }
    public String getEyeColor(){
        return this.eyeColor;
    }
    
    Cat(String e){
        this.setEyeColor(e);
    }
}

class Dog extends Animal{
    String furColor;
    public void setFurColor(String f){
        this.furColor = f;
    }
    public String getFurColor(){
        return this.furColor;
    }
    
    Dog (String d){
        this.setFurColor(d);
    }
}