Java中定义常量(Constant) 的几种方法 |
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为了方便大家交流Spark大数据,浪尖建了微信群,目前人数过多,只能通过浪尖或者在群里的朋友拉入群。纯技术交流,偶有吹水,但是打广告,不提醒,直接踢出。有兴趣加浪尖微信。 常量使用目的 1,为什么要将常亮提取出来? 2,提取出来怎么定义,定义在interface中,还是class中?有什么区别? 1)常亮提取出来有利于代码阅读,而且下次再做这种判断不用手写或复制,直接通过常量类就能得到,能够避免有的地方是username,有的地方是name来判断同一个逻辑含义相同变量问题。不过我觉得提取出来并不会有利于代码性能提升,因为常量分配在内存的常亮池中,所以内存不会出现多个相同常量字符串。总的来说提取常量主要是为了避免魔法数字和提高代码可读性。 2)常亮定义在final的class中,防止被其它类继承和实例化。定义在interface中性质也是一样,static final属性。但是interface看起来就是会被继承的。 interface中定义常量 采用接口(Interface)的中变量默认为static final的特性。 public interface ConstantInterface { String SUNDAY = "SUNDAY"; String MONDAY = "MONDAY"; String TUESDAY = "TUESDAY"; String WEDNESDAY = "WEDNESDAY"; String THURSDAY = "THURSDAY"; String FRIDAY = "FRIDAY"; String SATURDAY = "SATURDAY"; }Enum定义常量 enum ConstantEnum { SUNDAY, MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY, SATURDAY }普通类中定义常量 采用了在普通类中使用static final修饰变量的方法。 public 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"; }也可以使用get方法 public 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; } }final class定义常量 public final 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"; }推荐,使用final class定义,表面意思更清楚。虽然为了简单编码,浪尖采用的是interface。 |
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