如何在Java中定义常量(Constant)

首先看示例：

/** * 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/java/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

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