Java中定义常量(Constant) 的几种方法

• 方法一采用接口(Interface)的中变量默认为static final的特性

interface ConstantInterface {    
    String SUNDAY = "SUNDAY";    
    String MONDAY = "MONDAY";    
    String TUESDAY = "TUESDAY";    
    String WEDNESDAY = "WEDNESDAY";    
    String THURSDAY = "THURSDAY";    
    String FRIDAY = "FRIDAY";    
    String SATURDAY = "SATURDAY";    
}    

方法二采用了Java 5.0中引入的Enum类型

enum ConstantEnum {    
    SUNDAY, MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY, SATURDAY    
} 

方法三采用了在普通类中使用static final修饰变量的方法

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";    
}    

方法四类似方法三，但是通过函数来获取常量

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()));    
    }    
}    

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。