java中定义常量

/**
* 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】。