JDK5-枚举

1. 使用普通类模拟枚举

 public class Weekday {
     private Weekday() {} // 私有化

     public static final Weekday MONDAY = new Weekday();　　// 每个枚举都是一个对象
     public static final Weekday TUESDAY = new Weekday();

     public String toString() {
         if(this == MONDAY)
             return "Monday";
         else if(...) ...
     }
 }

2. 使用抽象类模拟枚举

 public abstract class Weekday {
     private Weekday() {}

     public final static Weekday MONDAY = new Weekday() {
         public Weekday nextDay() {
             return TUESDAY;
         }
     };

     public final static Weekday TUESDAY = new Weekday() {
         public Weekday nextDay() {
             return WEDNESDAY;
         }
     };

     ...

     public abstract Weekday nextDay();
 }

使用抽象类模拟可以免除写大量的if-else语句，不需要对每个对象进行判断，只需要有具体实现类完成即可

3. 枚举类

 public enum Weekday {
     SUN, MON, TUE, WED, THU, FRI, SAT
 }

普通的枚举类末尾不需要写分号

4. 带构造参数枚举

 public enum Weekday {
     SUN(5), MON(), TUE(7), WED(), THU(9), FRI, SAT;    // 必须第一行，且以分号结尾

     private Weekday() {}
     private Weekday(int number) {
         System.out.println(number);
     }
 }

枚举中每个变量都是static final的

5. 带抽象函数的枚举

 public enum Weekday {    // enum不用abstract修饰
     SUN(5) {
         public Weekday nextDay() {
             return MON;
         }
     },
     MON() {
         public Weekday nextDay() {
             return TUE;
         }
     },
     TUE() {
         public Weekday nextDay() {
             return WED;
         }
     },
     WED() {
         public Weekday nextDay() {
             return THU;
         }
     },
     THU() {
         public Weekday nextDay() {
             return FRI;
         }
     },
     FRI() {
         public Weekday nextDay() {
             return SAT;
         }
     },
     SAT() {
         public Weekday nextDay() {
             return SUN;
         }
     };

     private Weekday() {}
     private Weekday(int number) {
         System.out.println(number);
     }

     public abstract Weekday nextDay();
 }

6. 枚举类中的方法

　　toString()　　- String

　　name()　　- String

　　ordinal()　　- int

　　valueOf(String name)　　- Weekday

　　values()　　- Weekday[]