Java中枚举类

发表于 更新于 分类于 ， 阅读次数： Valine：

我们现在需要一个枚举出四季以及他们各自的特点，四季只有春夏秋冬这四个季节，而且特点固定，所以我们不需要用户去创建新的季节对象。

自定义枚举

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package Learn;
public class Test {
    public static void main(String[] args) {
        System.out.println(Season.SPRING.toString());
        System.out.println(Season.SUMMER.toString());
        System.out.println(Season.AUTUMN.toString());
        System.out.println(Season.WINTER.toString());
    }
}
class Season{
    private String season, characteristic;
    /**将构造其私有化，防止在main方法中直接new对象*/
    private Season(String season,String characteristic){
        this.season=season;
        this.characteristic=characteristic;
    }
    /**定义四个季节的特点,使用static使得在main方法中不用创建实例对象，但是会造成类的加载，所以再加上final变成常量值，避免了类的加载*/
   public static final Season SPRING =new Season("春天","温暖");
   public static final Season SUMMER =new Season("夏天","炎热");
   public static final Season AUTUMN =new Season("秋天","凉爽");
   public static  final Season WINTER =new Season("冬天","寒冷");

    @Override
    public String toString(){
        return season+characteristic;
    }

}

image-20220322084509210

  1. 不需要提供set方法，因为枚举对象值通常为只读。
  2. 对枚举对象属性使用final+static共同修饰，实现底层优化
  3. 枚举对象属于常量，通常全部大写

enum关键字枚举

将定义的常量对象定义在最前面

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package Learn;
public class Test {
    public static void main(String[] args) {
        System.out.println(Season.SPRING.toString());
        System.out.println(Season.SUMMER.toString());
        System.out.println(Season.AUTUMN.toString());
        System.out.println(Season.WINTER.toString());
    }
}
enum Season{
    SPRING("春天","温暖"),
    SUMMER ("夏天","炎热"),
    AUTUMN ("秋天","凉爽"),
    WINTER ("冬天","寒冷");
    private String season, characteristic;
    /**将构造其私有化，防止在main方法中直接new对象*/
    private Season(String season,String characteristic){
        this.season=season;
        this.characteristic=characteristic;
    }


    @Override
    public String toString(){
        return season+characteristic;
    }

}

image-20220322084543249

注意事项：

  • 当我们使用enum关键字时，默认会继承enum类，我们反编译一下文件，可以发现同时也是final类型点击并拖拽以移动image-20220322084630144

  • 如果使用无参构造器，则实参列表与小括号都可以省略。例如下面的OTHER

image-20220322084718169

  • img点击并拖拽以移动这个也是正确的，默认调用的无参构造器。

枚举中常用的方法

上面我们说到，enum其实是继承了ENUM类的，所以也会继承其方法

方法名 作用
name 输出对象的名字
ordinal 输出该对象在枚举中的位置（从0开始）
hascode 输出对应的对象地址编号
value 将枚举填入数组中
valueof 到对应的对象中去寻找，如果找到了，返回该对象，否则为false
compareTo 比较两个对象的枚举编号，是他们顺序号的差值，可以crtl+B查看源码 
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package Learn;
public class Test {
    public static void main(String[] args) {
        System.out.println(Season.SPRING.toString());
        System.out.println(Season.SUMMER.toString());
        System.out.println(Season.AUTUMN.toString());
        System.out.println(Season.WINTER.toString());
        System.out.println(Season.SPRING.name());
        System.out.println(Season.SPRING.hashCode());
        //输出相应的编号，编号从0开始
        System.out.println(Season.SPRING.ordinal());
        Season []values=Season.values();
        for (Season A :values){
            System.out.println(A);
        }
        System.out.println(Season.valueOf("SPRING"));
        //System.out.println(Season.valueOf("dj"));
        System.out.println(Season.SPRING.compareTo(Season.AUTUMN));

    }
}
enum Season{
    SPRING("春天","温暖"),
    SUMMER ("夏天","炎热"),
    AUTUMN ("秋天","凉爽"),
    WINTER ("冬天","寒冷"),
    OTHER;
    private String season, characteristic;
    /**将构造其私有化，防止在main方法中直接new对象*/
    private Season(){}
    private Season(String season,String characteristic){
        this.season=season;
        this.characteristic=characteristic;
    }


    @Override
    public String toString(){
        return season+characteristic;
    }

}

image-20220322084756180

练习：输出每一周的星期

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package Learn;

public class Exercise {
    public static void main(String[] args) {
        Week [] weeks= Week.values();
        for (Week week :weeks){
            System.out.println(week.toString());
        }

    }
}
enum Week{
    Monday("星期一"),
    Tuesday("星期二"),
    Wednesday("星期三"),
    Thursday("星期四"),
    Friday("星期五"),
    Saturday("星期六"),
    Sunday("星期日");

    private String week;
    Week(String week){
        this.week=week;
    }

    @Override
    public String toString() {
        return  week ;
    }
}

image-20220322084840211

注意：

如果我们使用enum关键字之后，就不可以继承其他类了，Java是单继承机制。但是实质上enum还是一个类，所以可以继承实现接口。