Java中定义常量(Constant) 的几种方法

    /** 
     * 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】。

原文链接：http://blog.csdn.net/autofei/article/details/6419460

参考

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