如何实现让一个类有固定个数的对象

手动封装构造方法（private） → 创建静态对象 → final修饰静态对象，使其成为常量

class Season { //枚举类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

从 JDK1.5 开始

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

反编译后，跟上一个步骤类似

枚举类的本质就是一个类，被final修饰了，不能有子类，继承了java.lang.Enum

枚举类方法

• int ordinal()
  返回枚举项的编号，每个枚举项都有一个编号，编号从0开始

  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)
  比较枚举项的大小，比较的是编号

  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()
  返回枚举常量的名称，与其枚举声明中声明的完全相同

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

• String toString()
  返回声明中包含的此枚举常量的名称

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

• static <T extends Enum> T value0f(Class enumType, String name)
  返回具有指定名称的指定枚举类型的枚举常量

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

• public static Week[] values()
  得到所有枚举项的数组

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

• public static Week valueOf(java.lang.String);
  返回具有指定名称的指定枚举类型的枚举常量

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

定义属性

enum中构造方法默认被private修饰

enum Season{SPRING("春季"),SUMMER("夏季"),AUTUMN("秋季"),WINTER("冬季");  private String desc;Season(){}  //默认就是privateSeason(String desc){//默认就是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);}
}

定义方法

静态、非静态方法

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举类前不用写abstract，在每个枚举项里都必须重写抽象方法

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();}
}

实现接口

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;  //多态Object obj=Season.WINTER;}
}

练习

定义一个Person类，有姓名和性别属性，性别定义成枚举

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("赵四",Gender.MALE);System.out.println(ren);//赵四，男}
}