枚举类的使用

1.枚举类的理解：类的对象只有有限个，确定的。我们称此类为枚举类
2.当需要定义一组常量时，强烈建议使用枚举类
3.如果枚举类中只有一个对象，则可以作为单例模式的实现方式

定义枚举类

方式一

jdk5.0之前，自定义枚举类

  1. public class SeasonTest {
  3.     public static void main(String[] args) {
  4.         Season spring = Season.SPRING;
  5.         System.out.println(spring);
  6.     }
  8. }
  9. //自定义枚举类
  10. class Season{
  12.     //1.声明Season对象的属性：private final修饰
  13.     private final String seasonName;
  14.     private final String seasonDesc;
  16.     //2.私有化类的构造器，并给对象属性赋值
  17.     private Season (String seasonName,String seasonDesc){
  18.         this.seasonName = seasonName;
  19.         this.seasonDesc = seasonDesc;
  20.     }
  22.     //3.提供当前枚举类的多个对象：public static final的
  23.     public static final Season SPRING = new Season("春天","春暖花开" );
  24.     public static final Season SUMMER = new Season("夏天","夏日炎炎" );
  25.     public static final Season AUTUMN = new Season("秋天","秋高气爽" );
  26.     public static final Season WINTER = new Season("冬天","冰树银花" );
  28.     //4.其他诉求：获取枚举类对象的属性
  29.     public String getSeasonName() {
  30.         return seasonName;
  31.     }
  33.     public String getSeasonDesc() {
  34.         return seasonDesc;
  35.     }
  36.     //5.提供toString方法
  38.     @Override
  39.     public String toString() {
  40.         return "Season{" +
  41.                 "seasonName='" + seasonName + '\'' +
  42.                 ", seasonDesc='" + seasonDesc + '\'' +
  43.                 '}';
  44.     }
  45. }

方式二

jdk5.0，可以使用enum关键字定义枚举类
说明：定义的枚举类默认继承于java.lang.Enum类

  1. public class SeasonTest1 {
  3.     public static void main(String[] args) {
  4.         Season1 summer = Season1.SUMMER;
  5.         System.out.println(summer);
  6.     }
  7. }
  8. //自定义枚举类
  9. enum Season1{
  11.     //1.提供当前枚举类的对象，多个对象之间用”,“隔开，最后一个对象”;“结束
  12.     SPRING ("春天","春暖花开" ),
  13.     SUMMER ("夏天","夏日炎炎" ),
  14.     AUTUMN ("秋天","秋高气爽" ),
  15.     WINTER ("冬天","冰树银花" );
  17.     //2.声明Season对象的属性：private final修饰
  18.     private final String seasonName;
  19.     private final String seasonDesc;
  21.     //3.私有化类的构造器，并给对象属性赋值
  22.     private Season1 (String seasonName,String seasonDesc){
  23.         this.seasonName = seasonName;
  24.         this.seasonDesc = seasonDesc;
  25.     }
  28.     //4.其他诉求：获取枚举类对象的属性
  29.     public String getSeasonName() {
  30.         return seasonName;
  31.     }
  33.     public String getSeasonDesc() {
  34.         return seasonDesc;
  35.     }
  36.     //5.提供toString方法
  38.     //@Override
  39.     //public String toString() {
  40.         //return "Season{" +
  41.                 //"seasonName='" + seasonName + '\'' +
  42.                 //", seasonDesc='" + seasonDesc + '\'' +
  43.                 //'}';
  44.     //}
  45. }

Enum类中常用方法

  1. //toString():
  2. System.out.println(summer.toString());
  4. //value():
  5. Season1[] values = Season1.values();
  6. for (int i =0;i < values.length;i++){
  7.     System.out.println(values[i]);
  8. }
  10. //valueOf(String objName):返回枚举类中对象名是objName的对象
  11. //如果没有objName的枚举类对象，则抛异常：IllegalArgumentException
  12. Season1 winter = Season1.valueOf("WINTER");
  13. System.out.println(winter);

enum关键字定义枚举类实现接口情况

①实现接口，在enum类中实现抽象方法

  1. interface Info{
  2.     void show();
  3. }
  6. public void show(){
  7.        System.out.println("这是一个季节");
  8.     }

②让枚举类的对象分别实现接口中的抽象方法

  1. interface Info{
  2.     void show();
  3. }
  5. SPRING ("春天","春暖花开" ){
  6.         @Override
  7.         public void show() {
  9.         }
  10.     },
  11.     SUMMER ("夏天","夏日炎炎" ){
  12.         @Override
  13.         public void show() {
  15.         }
  16.     },
  17.     AUTUMN ("秋天","秋高气爽" ){
  18.         @Override
  19.         public void show() {
  21.         }
  22.     },
  23.     WINTER ("冬天","冰树银花" ){
  24.         @Override
  25.         public void show() {
  27.         }
  28.     };