[Java知识库]Java——枚举(enum)简单实例讲解

一.枚举介绍

1.枚举是一组常量的集合
2.理解：美剧属于一种特殊的类，里面只包含一组有限的特定的对象

1.自定义枚举实现

1.不需要提供Set方法，枚举对象值通常为只读。
2.对枚举对象/属性使用final和static关键字修饰，实现底层优化
3.枚举对象名通常使用全部大写，常量的命名规范
4.枚举·对象根据需要，可以有一到多个属性

（1）示例

package com.demo;

import javax.sound.midi.Soundbank;

/**
 * @version 1.0
 * @auther Demo龙
 */
public class Enum01 {
    public static void main(String[] args) {
        System.out.println(Season.SPRING);
        System.out.println(Season.SUMMER);
        System.out.println(Season.AUTUMN);
        System.out.println(Season.WINTER);
    }
}
//演示自定义枚举实现
class Season{
    private String name;
    private String desc;//描述特性

    //1.将构造器私有化，目的防止直接new出来
    private Season(String name, String desc) {
        this.name = name;
        this.desc = desc;
    }
    //2.去掉set方法，只能读取，不能修改属性

    public String getName() {
        return name;
    }

    public String getDesc() {
        return desc;
    }
    //3.在season内部创建固定的对象
    //定义了四个对象
//    public static Season SPRING=new Season("春天","温暖");
//    public static Season SUMMER=new Season("夏天","炎热");
//    public static Season AUTUMN=new Season("秋天","凉爽");
//    public static Season WINTER=new Season("冬天","寒冷");
    //最终优化，加入final
    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");

    //重写toString方法
    @Override
    public String toString() {
        return "Season{" +
                "name='" + name + '\'' +
                ", desc='" + desc + '\'' +
                '}';
    }
}

（2）测试结果

2.enum关键字实现枚举

如果使用enum关键字来实现枚举类
1.使用关键字enum替换class
2.public static final Season02 SPRING=new Season02(“春天”,“温暖”);可替换为
SPRING(“春天”,“温暖”),//解读：常量名（实参列表）
3.如果有多个常量使用逗号间隔即可
4.如果使用enum关键字实现枚举，要求将定义的常量对象写下前面

（1）示例

package com.demo;

/**
 * @version 1.0
 * @auther Demo龙
 */
public class Enum02 {
    public static void main(String[] args) {
        System.out.println(Season.SPRING);
        System.out.println(Season.SUMMER);
        System.out.println(Season.AUTUMN);
        System.out.println(Season.WINTER);
    }
}
//演示使用enum关键字来实现枚举类
enum Season02{
    //如果使用enum关键字来实现枚举类
    //1.使用关键字enum替换class
    //2.public static final Season02 SPRING=new Season02("春天","温暖");可替换为

    SPRING("春天","温暖"),//解读：常量名（实参列表）
    //3.如果有多个常量使用逗号间隔即可
    SUMMER("夏天","炎热"),
    AUTUMN("秋天","凉爽"), WINTER("冬天","寒冷");
    //4.如果使用enum关键字实现枚举，要求将定义的常量对象写下前面
    private String name;
    private String desc;//描述特性

    //1.将构造器私有化，目的防止直接new出来
    private Season02(String name, String desc) {
        this.name = name;
        this.desc = desc;
    }
    //2.去掉set方法，只能读取，不能修改属性

    public String getName() {
        return name;
    }

    public String getDesc() {
        return desc;
    }
    //3.在season内部创建固定的对象
    //定义了四个对象
//    public static Season SPRING=new Season("春天","温暖");
//    public static Season SUMMER=new Season("夏天","炎热");
//    public static Season AUTUMN=new Season("秋天","凉爽");
//    public static Season WINTER=new Season("冬天","寒冷");
    //最终优化，加入final
//    public static final Season02 SPRING=new Season02("春天","温暖");
//    public static final Season02 SUMMER=new Season02("夏天","炎热");
//    public static final Season02 AUTUMN=new Season02("秋天","凉爽");
//    public static final Season02 WINTER=new Season02("冬天","寒冷");

    //重写toString方法
    @Override
    public String toString() {
        return "Season{" +
                "name='" + name + '\'' +
                ", desc='" + desc + '\'' +
                '}';
    }
}

（2）测试结果

3.enum关键字注意事项

1.当我i们使用enum关键字开发一个枚举类时，默认会继承Enum类
2.传统的public static final Season02 SPRING=new Season02("春天","温暖");，这里要知道他调用的是哪个构造器
3.如果使用无参构造器创建枚举对象，则实参列表和小括号都可以省略.
4.当有多个枚举对象时，使用逗号间隔，最后有一个分号结尾
5.枚举对象必须放在枚举类的行首

（1）示例

package com.demo;

/**
 * @version 1.0
 * @auther Demo龙
 */
public class Enum02 {
    public static void main(String[] args) {
        System.out.println(Season.SPRING);
        System.out.println(Season.SUMMER);
        System.out.println(Season.AUTUMN);
        System.out.println(Season.WINTER);
    }
}
//演示使用enum关键字来实现枚举类
enum Season02{
    //如果使用enum关键字来实现枚举类
    //1.使用关键字enum替换class
    //2.public static final Season02 SPRING=new Season02("春天","温暖");可替换为

    SPRING("春天","温暖"),//解读：常量名（实参列表）
    //3.如果有多个常量使用逗号间隔即可
    SUMMER("夏天","炎热"),
    AUTUMN("秋天","凉爽"), WINTER("冬天","寒冷"),
    //3.如果使用无参构造器创建枚举对象，则实参列表和小括号都可以省略.两种写法
    HAHA,//调用无参构造器
    HAHAHA();//调用无参构造器
    //4.如果使用enum关键字实现枚举，要求将定义的常量对象写下前面
    private String name;
    private String desc;//描述特性

    //1.将构造器私有化，目的防止直接new出来
    private Season02(String name, String desc) {
        this.name = name;
        this.desc = desc;
    }
    private Season02() {
        //无参构造器
    }
    //2.去掉set方法，只能读取，不能修改属性

    public String getName() {
        return name;
    }

    public String getDesc() {
        return desc;
    }
    //3.在season内部创建固定的对象
    //定义了四个对象
//    public static Season SPRING=new Season("春天","温暖");
//    public static Season SUMMER=new Season("夏天","炎热");
//    public static Season AUTUMN=new Season("秋天","凉爽");
//    public static Season WINTER=new Season("冬天","寒冷");
    //最终优化，加入final
//    public static final Season02 SPRING=new Season02("春天","温暖");
//    public static final Season02 SUMMER=new Season02("夏天","炎热");
//    public static final Season02 AUTUMN=new Season02("秋天","凉爽");
//    public static final Season02 WINTER=new Season02("冬天","寒冷");

    //重写toString方法
    @Override
    public String toString() {
        return "Season{" +
                "name='" + name + '\'' +
                ", desc='" + desc + '\'' +
                '}';
    }
}

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