共有四种方式：

1 /** 2  * Method One 3  * 定义接口类，采用接口(Interface)的中变量默认为static final的特性。 4  */ 5 interface ConstantInterface { 6     String SUNDAY = "SUNDAY"; 7     String MONDAY = "MONDAY"; 8     String TUESDAY = "TUESDAY"; 9     String WEDNESDAY = "WEDNESDAY";10     String THURSDAY = "THURSDAY";11     String FRIDAY = "FRIDAY";12     String SATURDAY = "SATURDAY";13 }14 /**15  * Method Two16  * 定义枚举17  */18 enum ConstantEnum {19     SUNDAY, MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY, SATURDAY20 }21 /**22  * Method Three23  * 定义常量类24  */25 class ConstantClassField {26     public static final String SUNDAY = "SUNDAY";27     public static final String MONDAY = "MONDAY";28     public static final String TUESDAY = "TUESDAY";29     public static final String WEDNESDAY = "WEDNESDAY";30     public static final String THURSDAY = "THURSDAY";31     public static final String FRIDAY = "FRIDAY";32     public static final String SATURDAY = "SATURDAY";33 }34 /**35  * Method Four36  * 定义bean37  */38 class ConstantClassFunction {39     private static final String SUNDAY = "SUNDAY";40     private static final String MONDAY = "MONDAY";41     private static final String TUESDAY = "TUESDAY";42     private static final String WEDNESDAY = "WEDNESDAY";43     private static final String THURSDAY = "THURSDAY";44     private static final String FRIDAY = "FRIDAY";45     private static final String SATURDAY = "SATURDAY";46     public static String getSunday() {47         return SUNDAY;48     }49     public static String getMonday() {50         return MONDAY;51     }52     public static String getTuesday() {53         return TUESDAY;54     }55     public static String getWednesday() {56         return WEDNESDAY;57     }58     public static String getThursday() {59         return THURSDAY;60     }61     public static String getFirday() {62         return FRIDAY;63     }64     public static String getSaturday() {65         return SATURDAY;66     }67 }68 69 /**70  * 测试代码71  * */72 class TestConstant {73     static final String day = "saturday";74     public static void main(String[] args) {75         System.out.println("Is today Saturday?");76         System.out.println(day.equalsIgnoreCase(ConstantInterface.SATURDAY));77         System.out.println(day.equalsIgnoreCase(ConstantEnum.SATURDAY.name()));78         System.out.println(day.equalsIgnoreCase(ConstantClassField.SATURDAY));79         System.out.println(day.equalsIgnoreCase(ConstantClassFunction.getSaturday()));80     }81 }

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(枚举)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，类似bean，也就是有自带的get方法。

 

使用常量类原因：

定义全局变量会增加程序耦合成都。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，否则方法二是最为推荐。方法三是比较直观。方法一和方法三本质上一样。方法四提供了灵活性。