【Java基础】枚举（二）

• 1 枚举的使用场景
• 2 如何定义一个枚举类
• 3 `Enum`类的主要方法
• • 3.1 `values()`方法
  • 3.2 `valueOf(String str)`方法
  • 3.3 `toString()`方法
• 4 枚举类的对象分别实现接口的抽象方法

• 类的对象只有有限个，且是确定的

如：
订单的状态{已下单，待支付，已支付，已完成}
季节{春、夏、秋、冬}
星期{一、二、三、四、五、六、七}

• 当需要定义一组常量时，一般会用枚举类。

• 若枚举类中只有一个对象，则可以作为一种单例模式的实现方式

• jdk1.5之前，自定义枚举类

public class SeasonTest {
    public static void main(String[] args) {
        Season spring = Season.SPRING;
        System.out.println(spring);
    }
}


class Season {
    // 1、声明Season对象的属性，使用private final修饰
    private final String seasonName;
    private final String seasonDesc;

    // 2、构造方法私有
    private Season(String seasonName, String seasonDesc) {
        this.seasonName = seasonName;
        this.seasonDesc = seasonDesc;
    }

    // 3、提供枚举类的多个对象，使用public static final修饰
    public static final Season SPRING = new Season("春天","春暖花开");
    public static final Season SUMMER = new Season("夏天","夏日烟火");
    public static final Season AUTUMN = new Season("秋天","秋风落叶");
    public static final Season WINTER = new Season("冬天","冬泳怪鸽");

    // 4、获取属性的get方法和toString方法使用public修饰
    public String getSeasonName() {
        return seasonName;
    }

    public String getSeasonDesc() {
        return seasonDesc;
    }

    @Override
    public String toString() {
        return "Season{" +
                "seasonName='" + seasonName + ''' +
                ", seasonDesc='" + seasonDesc + ''' +
                '}';
    }
}

• jdk1.5之后，使用enum关键字定义枚举类

public class SeasonTest1 {
    public static void main(String[] args) {
        Season1 spring = Season1.SPRING;
        System.out.println(spring);
    }
}


enum Season1 {
    // 1、枚举类的对象，多个对象之间使用","隔开，末尾对象使用";"结束
    SPRING("春天","春暖花开"),

    SUMMER("夏天","夏日烟火"),

    AUTUMN("秋天","秋风落叶"),

    WINTER("冬天","冬泳怪鸽");

    // 2、声明Season对象的属性，使用private final修饰
    private final String seasonName;
    private final String seasonDesc;

    // 3、构造方法默认私有
    Season1(String seasonName, String seasonDesc) {
        this.seasonName = seasonName;
        this.seasonDesc = seasonDesc;
    }

    // 4、获取属性的get方法和toString方法使用public修饰
    public String getSeasonName() {
        return seasonName;
    }

    public String getSeasonDesc() {
        return seasonDesc;
    }

    // 5、toString方法已经被重写
    @Override
    public String toString() {
        return "Season{" + "seasonName='" + seasonName + ''' + ", seasonDesc='" + seasonDesc + ''' + '}';
    }
}

• 返回枚举的对象数组，可以遍历所有的枚举值

Season1[] season1s = Season1.values();
for (Season1 season1 : season1s) {
    System.out.println(season1);
}

• 把一个字符串转换为对应的枚举类对象，该字符串必须是枚举类对象的名称

System.out.println(Season1.valueOf("SPRING"));
System.out.println(Season1.valueOf("SUMMER"));
System.out.println(Season1.valueOf("AUTUMN"));
System.out.println(Season1.valueOf("WINTER"));

• 返回枚举类对象的名称

public class SeasonTest2 {
    public static void main(String[] args) {
        Season2[] season2s = Season2.values();
        for (Season2 season2 : season2s) {
            System.out.println(season2);
            season2.show();
        }
    }
}

interface info {
    void show();
}

enum Season2 implements info {
    SPRING("春天", "春暖花开") {
        @Override
        public void show() {
            System.out.println("这是春天的show方法");
        }
    },

    SUMMER("夏天", "夏日烟火") {
        @Override
        public void show() {
            System.out.println("这是夏天的show方法");
        }
    },

    AUTUMN("秋天", "秋风落叶") {
        @Override
        public void show() {
            System.out.println("这是秋天的show方法");
        }
    },

    WINTER("冬天", "冬泳怪鸽") {
        @Override
        public void show() {
            System.out.println("这是冬天的show方法");
        }
    };

    private final String seasonName;
    private final String seasonDesc;

    Season2(String seasonName, String seasonDesc) {
        this.seasonName = seasonName;
        this.seasonDesc = seasonDesc;
    }

    public String getSeasonName() {
        return seasonName;
    }

    public String getSeasonDesc() {
        return seasonDesc;
    }
}

参考资料
【1】https://www.bilibili.com/video/BV1Kb411W75N?p=498&vd_source=57da47e21dacf219d3e527efc72514b6