共有四种方式：
1 /** 2 * Method One 3 * 定义接口类，采用接口(Interface)的中变量默认为static final的特性。 4 */ 5 interface ConstantInterface { 6 String SUNDAY = "SUNDAY"; 7 String MONDAY = "MONDAY"; 8 String TUESDAY = "TUESDAY"; 9 String WEDNESDAY = "WEDNESDAY"; 10 String THURSDAY = "THURSDAY"; 11 String FRIDAY = "FRIDAY"; 12 String SATURDAY = "SATURDAY"; 13 } 14 /** 15 * Method Two 16 * 定义枚举 17 */ 18 enum ConstantEnum { 19 SUNDAY, MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY, SATURDAY 20 } 21 /** 22 * Method Three 23 * 定义常量类 24 */ 25 class ConstantClassField { 26 public static final String SUNDAY = "SUNDAY"; 27 public static final String MONDAY = "MONDAY"; 28 public static final String TUESDAY = "TUESDAY"; 29 public static final String WEDNESDAY = "WEDNESDAY"; 30 public static final String THURSDAY = "THURSDAY"; 31 public static final String FRIDAY = "FRIDAY"; 32 public static final String SATURDAY = "SATURDAY"; 33 } 34 /** 35 * Method Four 36 * 定义bean 37 */ 38 class ConstantClassFunction { 39 private static final String SUNDAY = "SUNDAY"; 40 private static final String MONDAY = "MONDAY"; 41 private static final String TUESDAY = "TUESDAY"; 42 private static final String WEDNESDAY = "WEDNESDAY"; 43 private static final String THURSDAY = "THURSDAY"; 44 private static final String FRIDAY = "FRIDAY"; 45 private static final String SATURDAY = "SATURDAY"; 46 public static String getSunday() { 47 return SUNDAY; 48 } 49 public static String getMonday() { 50 return MONDAY; 51 } 52 public static String getTuesday() { 53 return TUESDAY; 54 } 55 public static String getWednesday() { 56 return WEDNESDAY; 57 } 58 public static String getThursday() { 59 return THURSDAY; 60 } 61 public static String getFirday() { 62 return FRIDAY; 63 } 64 public static String getSaturday() { 65 return SATURDAY; 66 } 67 } 68 69 /** 70 * 测试代码 71 * */ 72 class TestConstant { 73 static final String day = "saturday"; 74 public static void main(String[] args) { 75 System.out.println("Is today Saturday?"); 76 System.out.println(day.equalsIgnoreCase(ConstantInterface.SATURDAY)); 77 System.out.println(day.equalsIgnoreCase(ConstantEnum.SATURDAY.name())); 78 System.out.println(day.equalsIgnoreCase(ConstantClassField.SATURDAY)); 79 System.out.println(day.equalsIgnoreCase(ConstantClassFunction.getSaturday())); 80 } 81 }
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(枚举)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，类似bean，也就是有自带的get方法。
使用常量类原因：
定义全局变量会增加程序耦合成都。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，否则方法二是最为推荐。方法三是比较直观。方法一和方法三本质上一样。方法四提供了灵活性。