如何让在JAVA中定义常量池

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】。