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 美国高防vps {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。
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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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参考
【1】http://www.ibm.com/developerworks/cn/java/l-java-interface/index.html
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