学步园

首先看示例：

/**<br /> * Method One<br /> */<br /> interface ConstantInterface {<br /> String SUNDAY = "SUNDAY";<br /> String MONDAY = "MONDAY";<br /> String TUESDAY = "TUESDAY";<br /> String WEDNESDAY = "WEDNESDAY";<br /> String THURSDAY = "THURSDAY";<br /> String FRIDAY = "FRIDAY";<br /> String SATURDAY = "SATURDAY";<br /> }<br /> /**<br /> * Method Two<br /> */<br /> enum ConstantEnum {<br /> SUNDAY, MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY, SATURDAY<br /> }<br /> /**<br /> * Method Three<br /> */<br /> class ConstantClassField {<br /> public static final String SUNDAY = "SUNDAY";<br /> public static final String MONDAY = "MONDAY";<br /> public static final String TUESDAY = "TUESDAY";<br /> public static final String WEDNESDAY = "WEDNESDAY";<br /> public static final String THURSDAY = "THURSDAY";<br /> public static final String FRIDAY = "FRIDAY";<br /> public static final String SATURDAY = "SATURDAY";<br /> }<br /> /**<br /> * Method Four<br /> * http://www.ibm.com/developerworks/cn/java/l-java-interface/index.html<br /> */<br /> class ConstantClassFunction {<br /> private static final String SUNDAY = "SUNDAY";<br /> private static final String MONDAY = "MONDAY";<br /> private static final String TUESDAY = "TUESDAY";<br /> private static final String WEDNESDAY = "WEDNESDAY";<br /> private static final String THURSDAY = "THURSDAY";<br /> private static final String FRIDAY = "FRIDAY";<br /> private static final String SATURDAY = "SATURDAY";<br /> public static String getSunday() {<br /> return SUNDAY;<br /> }<br /> public static String getMonday() {<br /> return MONDAY;<br /> }<br /> public static String getTuesday() {<br /> return TUESDAY;<br /> }<br /> public static String getWednesday() {<br /> return WEDNESDAY;<br /> }<br /> public static String getThursday() {<br /> return THURSDAY;<br /> }<br /> public static String getFirday() {<br /> return FRIDAY;<br /> }<br /> public static String getSaturday() {<br /> return SATURDAY;<br /> }<br /> }<br /> public class TestConstant {<br /> static final String day = "saturday";<br /> public static void main(String[] args) {<br /> System.out.println("Is today Saturday?");<br /> System.out.println(day.equalsIgnoreCase(ConstantInterface.SATURDAY));<br /> System.out.println(day.equalsIgnoreCase(ConstantEnum.SATURDAY.name()));<br /> System.out.println(day.equalsIgnoreCase(ConstantClassField.SATURDAY));<br /> System.out.println(day.equalsIgnoreCase(ConstantClassFunction<br /> .getSaturday()));<br /> }<br /> } 

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