java中定义常量

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/**  * 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/javase" class='replace_word' title="Java SE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】。

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