如何在Java中定义常量(Constant)

原本引自  http://blog.csdn.net/autofei/article/details/6419460

 /**
  * Method One
  */
 interface ConstantInterface {
     String SUNDAY = "SUNDAY";
     String MONDAY = "MONDAY";
     String TUESDAY = "TUESDAY";
     String WEDNESDAY = "WEDNESDAY";
     String THURSDAY = "THURSDAY";
     String FRIDAY = "FRIDAY";
     String SATURDAY = "SATURDAY";
 }
 /**
  * Method Two
  */
 enum ConstantEnum {
     SUNDAY, MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY, SATURDAY
 }
 /**
  * Method Three
  */
 class ConstantClassField {
     public static final String SUNDAY = "SUNDAY";
     public static final String MONDAY = "MONDAY";
     public static final String TUESDAY = "TUESDAY";
     public static final String WEDNESDAY = "WEDNESDAY";
     public static final String THURSDAY = "THURSDAY";
     public static final String FRIDAY = "FRIDAY";
     public static final String SATURDAY = "SATURDAY";
 }
 /**
  * Method Four
  * http://www.ibm.com/developerworks/cn/<a href="http://lib.csdn.net/base/17" class='replace_word' title="Java EE知识库" target='_blank' style='color:#df3434; font-weight:bold;'>Java</a>/l-java-interface/index.html
  */
 class ConstantClassFunction {
     private static final String SUNDAY = "SUNDAY";
     private static final String MONDAY = "MONDAY";
     private static final String TUESDAY = "TUESDAY";
     private static final String WEDNESDAY = "WEDNESDAY";
     private static final String THURSDAY = "THURSDAY";
     private static final String FRIDAY = "FRIDAY";
     private static final String SATURDAY = "SATURDAY";
     public static String getSunday() {
         return SUNDAY;
     }
     public static String getMonday() {
         return MONDAY;
     }
     public static String getTuesday() {
         return TUESDAY;
     }
     public static String getWednesday() {
         return WEDNESDAY;
     }
     public static String getThursday() {
         return THURSDAY;
     }
     public static String getFirday() {
         return FRIDAY;
     }
     public static String getSaturday() {
         return SATURDAY;
     }
 }
 public class TestConstant {
     static final String day = "saturday";
     public static void main(String[] args) {
         System.out.println("Is today Saturday?");
         System.out.println(day.equalsIgnoreCase(ConstantInterface.SATURDAY));
         System.out.println(day.equalsIgnoreCase(ConstantEnum.SATURDAY.name()));
         System.out.println(day.equalsIgnoreCase(ConstantClassField.SATURDAY));
         System.out.println(day.equalsIgnoreCase(ConstantClassFunction
                 .getSaturday()));
     }
 }

方法一采用接口(Interface)的中变量默认为static final的特性

方法二采用了Java 5.0中引入的Enum类型。

方法三采用了在普通类中使用static final修饰变量的方法。

方法四类似方法三，但是通过函数来获取常量。

首先定义全局变量似乎有违Java的面向对象的封装特性，增加的耦合。所以最佳的方法是避免定义全局变量。如果是参数等，可以写入配置文件。如果实在是必须的，方法二是最为推荐的。方法三是大家都能想到的，非常的直观。方法一和方法三本质上一样。方法四提供了灵活性，具体参考引用【1】。

参考

http://www.ibm.com/developerworks/cn/java/l-java-interface/index.html