如何實現讓一個類有固定個數的對象

手動封裝構造方法（private） → 創建靜態對象 → final修飾靜態對象，使其成為常量

class Season { //枚舉類public final static Season SPRING = new Season();public final static Season SUMMER = new Season();public final static Season SUTUMN = new Season();public final static Season WINTER = new Season();private Season() {}public void show() {System.out.println("hello");}
}
class Demo7 {public static void main(String[] args) {Season chunji = Season.SPRING;chunji.show();}
}

enum

從 JDK1.5 開始

enum Season {SPRING,SUMMER,AUTUMN,WINTER  //枚舉項，枚舉常量
}
class Demo7{public static void main(String[] args) {Season chunji = Season.SPRING;chunji.show();}
}

反編譯后，跟上一個步驟類似

枚舉類的本質就是一個類，被final修飾了，不能有子類，繼承了java.lang.Enum

枚舉類方法

• int ordinal()
  返回枚舉項的編號，每個枚舉項都有一個編號，編號從0開始

  enum Week{MONDAY,TUESDAY,WEDNESDAY,THURSDAY,FRIDAY,SATURDAY,SUNDAY
  }
  class Demo10{public static void main(String[] args){Week[] weeks={Week.MONDAY,Week.TUESDAY,Week.WEDNESDAY,Week.THURSDAY,Week.FRIDAY,Week.SATURDAY,Week.SUNDAY};System.out.println(weeks[0].ordinal());//0System.out.println(weeks[2].ordinal());//2System.out.println(weeks[6].ordinal());//6
  

• int compareTo(E o)
  比較枚舉項的大小，比較的是編號

  System.out.println(weeks[6].compareTo(weeks[2]));//4
  System.out.println(weeks[2].compareTo(weeks[4]));//-2
  System.out.println(weeks[2].compareTo(weeks[2]));//0
  

• String name()
  返回枚舉常量的名稱，與其枚舉聲明中聲明的完全相同

  System.out.println(weeks[6].name());//SUNDAY
  System.out.println(weeks[4].name());//FRIDAY
  

• String toString()
  返回聲明中包含的此枚舉常量的名稱

  System.out.println(weeks[6].toString());//SUNDAY
  System.out.println(weeks[4].toString());//FRIDAY
  

• static <T extends Enum> T value0f(Class enumType, String name)
  返回具有指定名稱的指定枚舉類型的枚舉常量

  Week obj = Enum.valueOf(Week.class,"MONDAY"); //MONDAY
  

• public static Week[] values()
  得到所有枚舉項的數組

  Week[] arr = Week.values();
  for(Week wk:arr)System.out.println(wk);//MONDAY TUESDAY WEDNESDAY ……
  

• public static Week valueOf(java.lang.String);
  返回具有指定名稱的指定枚舉類型的枚舉常量

  Week xingqi = Week.valueOf("MONDAY");
  System.out.println(xingqi);//MONDAY
  

定義屬性

enum中構造方法默認被private修飾

enum Season{SPRING("春季"),SUMMER("夏季"),AUTUMN("秋季"),WINTER("冬季");  private String desc;Season(){}  //默認就是privateSeason(String desc){//默認就是privatethis.desc=desc;}public String getDesc(){return desc;}public String toString(){return desc;} 
}
class Demo11{public static void main(String[] args){Season ss = Season.SUMMER;System.out.println(ss);}
}

定義方法

靜態、非靜態方法

enum Season{……………………public static void show(){System.out.println("Hello");}public void fun(){System.out.println("fun");}
}
class  Demo12 
{public static void main(String[] args) {Season xiaji=Season.SUMMER;xiaji.show();xiaji.fun();}
}

抽象方法

含有抽象方法前的枚舉類前不用寫abstract，在每個枚舉項里都必須重寫抽象方法

enum Season{SPRING("春季"){public void show(){System.out.println("春季");}},SUMMER("夏季"){public void show(){System.out.println("夏季");}},AUTUMN("秋季"){public void show(){System.out.println("秋季");}},WINTER("冬季"){public void show(){System.out.println("冬季");}};  ……………………public abstract void show();
}
class Demo13 
{public static void main(String[] args){Season.WINTER.show();}
}

實現接口

interface inter{void ff();
}
enum Season implements inter{SPRING("春季"),SUMMER("夏季"),AUTUMN("秋季"),WINTER("冬季");  ………………public void ff(){System.out.println("ok");}
}
class Demo14{public static void main(String[] args){Season.AUTUMN.ff();Enum  jijie=Season.WINTER;  //多態Object obj=Season.WINTER;}
}

練習

定義一個Person類，有姓名和性別屬性，性別定義成枚舉

enum Gender{MALE("男"),FEMALE("女");private String desc;Gender(){}Gender(String desc){this.desc=desc;}public String toString(){return desc;}
}
class Person{private String name;private Gender sex;Person(){}Person(String name,Gender sex){this.name=name;this.sex=sex;}public String toString(){return name+","+sex;}
}
class Demo15 {public static void main(String[] args) {Person ren=new Person("趙四",Gender.MALE);System.out.println(ren);//趙四，男}
}