Java 枚举 Enumeration

　　　　

枚举:

1. 自定义枚举类
2. 使用enum关键字

 

1. 不需要提供setXxx方法, 枚举对象通常只读
2. 对枚举对象使用static final, 实现底层优化
3. 枚举对象可有多个属性

package com.gibe;

public class Enumeration {
  public static void main(String[] args) {
    System.out.println(Season.AUTUMN);
    System.out.println(Season.WINTER);
  }
}

class Season {
  private String name;
  private String desc;
  // 定义四个固定类属性
  public static final Season SPRING = new Season("spring", "warm");
  public static final Season SUMMER = new Season("summber", "hot");
  public static final Season AUTUMN = new Season("autumn", "cool");
  public static final Season WINTER = new Season("winter", "cold");

  // 构造器私有, 防止new
  // 去掉setXxx, 防止属性被修改
  // 在类内部, 直接创建固定对象
  // 加入final
  private Season(String name, String desc) {
    this.name = name;
    this.desc = desc;
  }

  public String getName() {
    return name;
  }

  public String getDesc() {
    return desc;
  }

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

　　

steps:

1. 构造器私有化
2. 本类内部创建对象
3. 对外暴露对象 (public static final)
4. 提供get方法, 不提供set方法

 

package com.gibe;

public class Enumeration {
  public static void main(String[] args) {
    System.out.println(Season.AUTUMN);
    System.out.println(Season.WINTER);
  }
}

enum Season {
  SPRING("spring", "warm"), WINTER("winter", "cold"),
  AUTUMN("autumn", "cool"), SUMMER("summer", "hot");

  private String name;
  private String desc;

  private Season() {
  }

  private Season(String name, String desc) {
    this.name = name;
    this.desc = desc;
  }

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

  public String getName() {
    return name;
  }

  public String getDesc() {
    return desc;
  }
}

　　

1. 使用enum关键字开发枚举类时,默认继承Enum类,而且时一个final类, javap 反编译
2. 传统的 public static final Season2 SPRING = new Season2("春天", "温暖"); 简化成 SPRING("春天", "温暖")， 这里必 须知道，它调用的是哪个构造器
3. 使用无参构造器 创建 枚举对象, 实参列表 () 都可省

 

enum Gender{
    BOY,GIRL;  // 调用了Gender类的无参构造器
}

　　

 enum枚举类方法

1. name() 返回枚举类名称
2. ordinal() 从 0 编号
3. values() 反编译才能看到,返回 数组 含有定义所有枚举对象
   

    

    

4. valueOf() 从String转为 enum对象
5. compareTo 比较enum对象ordinal

package com;

public class Enumeration {
  public static void main(String[] args) {
    Season autumn = Season.AUTUMN;
    System.out.println(autumn.name());  // AUTUMN
    System.out.println(autumn.ordinal());  // 2
    Season[] values = Season.values();
    for (Season value : values) System.out.println(value);
    Season autumn_ = Season.valueOf("AUTUMN");
    System.out.println(autumn==autumn_);  // true
    System.out.println(Season.AUTUMN.compareTo(Season.SPRING));  // 2
  }
}

enum Season {
  SPRING("spring", "warm"), SUMMER("summer", "hot"), AUTUMN("autumn", "cool"), WINTER("winter", "cold");
  private String name;
  private String desc;

  private Season() {
  }

  Season(String name, String desc) {
    this.name = name;
    this.desc = desc;
  }

  public String getName() {
    return name;
  }

  public String getDesc() {
    return desc;
  }
}

　　

Notice:

1. 使用enum关键字后, 不能在继承其他类, enum会隐式继承Enum, Java单继承机制

    

    

2. enum实现的枚举类, 可以实现接口
   

   package com;
   
   public class Enumeration {
     public static void main(String[] args) {
       Music.music.play();
     }
   }
   
   interface Play{
     public abstract void play();
   }
   
   enum Music implements Play{
     music;
     @Override
     public void play(){
       System.out.println("playing ...");
     }
   }