java enum 举例

1、定义一个enum
public enum Grade { A, B, C, D, F, INCOMPLETE };
2、使用一个enum
private Grade grade;
public void assignGrade(Grade grade) {

           this.grade = grade;

         }
         public Grade getGrade() {

           return grade;

         }
public void testGradeAssignment(PrintStream out) throws IOException {

          student1.assignGrade(Grade.B);

          student2.assignGrade(Grade.INCOMPLETE);

          student3.assignGrade(Grade.A);

        }
3、类内声明Enum
public class Downloader {
       public enum DownloadStatus { INITIALIZING, IN_PROGRESS, COMPLETE };
       // Class body
}
PS.Enum默认是static的，就像interface默认是abstract的一样。
4、遍历Enum
重要是values（）这个方法，它返回该类型所有可能取值的集合。
public void listGradeValues(PrintStream out) throws IOException {

        Grade[] gradeValues = Grade.values();
        // for loop

        for (int i=0; i<gradeValues.length; i++) {

          out.println("Allowed value: '" + gradeValues[i] + "'");

        }
        // for/in loop

        for (Grade g : gradeValues ) {

          out.println("Allowed value: '" + g + "'");

        }

      }
5、Enum对switch的支持
public void testSwitchStatement(PrintStream out) throws IOException {

       StringBuffer outputText = new StringBuffer(student1.getFullName());
       switch (student1.getGrade()) {

         case A: 

           outputText.append(" excelled with a grade of A");

           break;   

         case B: // fall through to C

         case C: 

           outputText.append(" passed with a grade of ")

                     .append(student1.getGrade().toString());

           break;

         case D: // fall through to F

         case F:

           outputText.append(" failed with a grade of ")

                     .append(student1.getGrade().toString());

           break;

         case INCOMPLETE:

           outputText.append(" did not complete the class.");

           break;

         default:

           outputText.append(" has a grade of ")

                     .append(student1.getGrade().toString());

           break;

       }
6、EnumMap的使用
public enum AntStatus {

    INITIALIZING,

    COMPILING,

    COPYING,

    JARRING,

    ZIPPING,

    DONE,

    ERROR

}
public class AntStatusTester {
    public AntStatusTester() { }
    public void testEnumMap(PrintStream out) throws IOException {

      // Create a map with the key and a String message

      EnumMap<AntStatus, String> antMessages =

        new EnumMap<AntStatus, String>(AntStatus.class);
      // Initialize the map

      antMessages.put(AntStatus.INITIALIZING, "Initializing Ant...");

      antMessages.put(AntStatus.COMPILING,      "Compiling
Java classes...");

      antMessages.put(AntStatus.COPYING,        "Copying files...");

      antMessages.put(AntStatus.JARRING,        "JARring up files...");

      antMessages.put(AntStatus.ZIPPING,        "ZIPping up files...");

      antMessages.put(AntStatus.DONE,           "Build complete.");

      antMessages.put(AntStatus.ERROR,          "Error occurred.");
      // Iterate and print messages

      for (AntStatus status : AntStatus.values() ) {

        out.println("For status " + status + ", message is: " +

                    antMessages.get(status));

      }

    }
    public static void main(String[] args) {

      try {

        AntStatusTester tester = new AntStatusTester();
        tester.testEnumMap(System.out);

      } catch (IOException e) {

        e.printStackTrace();

      }

    }

}
7、Enum中添加method
public enum xxx{
xxx(){
}//构造函数
public int getXxx(){
}//接口
}

例一：

[java]
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package com.test4;  
  
public enum Day {  
    SUNDAY, MONDAY, TUESDAY, WEDNESDAY,   
    THURSDAY, FRIDAY, SATURDAY   
}  

[java]
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package com.test4;  
  
public class EnumTest {  
    Day day;  
  
    public EnumTest(Day day) {  
        this.day = day;  
    }  
  
    public void tellItLikeItIs() {  
        switch (day) {  
        case MONDAY:  
            System.out.println("Mondays are bad.");  
            break;  
  
        case FRIDAY:  
            System.out.println("Fridays are better.");  
            break;  
  
        case SATURDAY:  
        case SUNDAY:  
            System.out.println("Weekends are best.");  
            break;  
  
        default:  
            System.out.println("Midweek days are so-so.");  
            break;  
        }  
    }  
  
    public static void main(String[] args) {  
        EnumTest firstDay = new EnumTest(Day.MONDAY);  
        firstDay.tellItLikeItIs();  
        EnumTest thirdDay = new EnumTest(Day.WEDNESDAY);  
        thirdDay.tellItLikeItIs();  
        EnumTest fifthDay = new EnumTest(Day.FRIDAY);  
        fifthDay.tellItLikeItIs();  
        EnumTest sixthDay = new EnumTest(Day.SATURDAY);  
        sixthDay.tellItLikeItIs();  
        EnumTest seventhDay = new EnumTest(Day.SUNDAY);  
        seventhDay.tellItLikeItIs();  
  
    }  
}  

结果：

Mondays are bad.

Midweek days are so-so.

Fridays are better.

Weekends are best.

Weekends are best.