java如何在一个只能由类修改而不能由其实例修改的类中生成静态变量？

Question

如何创建只能由类修改而不能由其实例修改的类变量

class BullDog{
    String name;
    static String breed = "BullDog";

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

public class MainClass{
    public static void main(String [] args){
        Dog Mydog = new BullDog("Fluffy");
        Mydog.breed = "Shepherd"; // Should not be modified

        System.out.Println(Dog.breed);
    }
}

实际产出：

Shepherd

期望输出：

BullDog

Answer 1

将静态变量设为私有。有关详细信息，请参阅this

Answer 2

使字段final保持不变。而且static final是在班级层面

public class BullDog {
    public String name;
    public static final String breed = "BullDog";

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

问题是继承是不可能的。贵宾犬需要自己的静态品种，你不能让狗提供一个品种

public abstract class Dog {
    public String name;

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

    public abstract String getBreed();   
}

public class BullDog extends Dog {

    public BullDog(String name){
        super(name);
    }

    @Override
    public String getBreed() {
        return "Bulldog";
    }
}

public class Poodle extends Dog {

    public Poodle(String name){
        super(name);
    }

    @Override
    public String getBreed() {
        return "Wolf";
    }
}

List<Dog> dogs = Arrays.asList(new BullDog("fluffy"), new Poodle("Herman"));