Java enum 枚举类

本文主要是介绍Java enum 枚举类，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！

Java Enum 枚举类

概述

枚举类型本质上也是一种类，只不过是这个类的对象是有限的、固定的几个，不能让用户随意创建。

如果针对于某个类，其实例是确定个数，则推荐将此类声明为枚举类。

如果枚举类的实例只有一个，则可以看作时单例的实现方式。

枚举类的实现

JDK5.0之前

class Season{//2.声明当前类的对象的实例对象 使用Final修饰private final String seasonName;  //季节的名称private final String seasonDesc;  //季节的描述//1.0 私有化列表构造器private Season(String seasonName, String seasonDesc) {this.seasonName = seasonName;this.seasonDesc = seasonDesc;}//3.提供实力变量的get方法public String getSeasonName() {return seasonName;}public String getSeasonDesc() {return seasonDesc;}//4.创建当前类的实例 public static final Season SPRING = new Season("春天","春暖花开");public static final Season SUMMER = new Season("夏天","夏日炎炎");public static final Season AUTUMN = new Season("秋天","秋高气爽");public static final Season WINTER = new Season("冬天","白雪皑皑");//还可以重写toString方法}

JDK5.0之中

num Season1{//必须在枚举类开头 声明对象 中间使用,隔开(枚举类中需要声明了私有化构造器)SPRING("春天","春暖花开"),SUMMER("夏天","夏日炎炎"),AUTUMN("秋天","秋高气爽"),WINTER("冬天","白雪皑皑");private final String seasonName;    //季节名称(使用final修饰，当作常量，不允许更改)private final String seasonDesc;    //季节描述//提供私有化构造器private Season1(String seasonName,String seasonDesc){this.seasonName = seasonName;this.seasonDesc = seasonDesc;}

细节

使用enum关键字定义的枚举类，默认其父类时java.lang.Enum类
使用enum关键字定义的枚举类，不要再显示的定义其父类，否则报错

enum类中的方法

已经定义了enum类

enum Season {SPRING("春季","春风又绿江南岸"),SUMMER("夏季","映日荷花别样红"),AUTUMN("秋季","秋水共长天一色"),WINTER("冬季","千里冰封，万里雪飘");private final String seasonName;    //季节名称private final String seasonDesc;    //季节描述private Season(String seasonName, String seasonDesc){this.seasonName = seasonName;this.seasonDesc = seasonDesc;}public String getSeasonName() {return seasonName;}public String getSeasonDesc() {return seasonDesc;}
}

toString() 默认返回的是常量名（对象名），可以继续手动重写该方法！

public class SeasonTest{public static void main(String []args){System.out.println(Season.SPRING.toString());	//输出：SPRINGSystem.out.println(Season.SUMMER.toString());	//输出：SUMMERSystem.out.println(Season.AUTUMN.toString());	//输出：AUTUMNSystem.out.println(Season.WINTER.toString());	//输出：WINTERSystem.out.println(Season.SPRING); 				//输出：SPRINGSystem.out.println(Season.SUMMER);				//输出：SUMMERSystem.out.println(Season.AUTUMN);				//输出: AUTUMNSystem.out.println(Season.WINTER);				//输出：WINTER}
}
//未重写toSpring()的结果
String toString(): 默认返回的是常量名（对象名），可以继续手动重写该方法！

name() 得到当前枚举常量的名称。建议优先使用toString()。

public class SeasonTest{public static void main(String []args){System.out.println(Season.SPRING.name());System.out.println(Season.SUMMER.name());System.out.println(Season.AUTUMN.name());System.out.println(Season.WINTER.name());}
}
//输出结果
//SPRING
//SUMMER
//AUTUMN
//WINTER
String name():得到当前枚举常量的名称。建议优先使用toString()。

values()

public class SeasonTest{public static void main(String []args){Season[] values = Season.values();for (int i = 0; i < values.length; i++) {System.out.println(values[i]);}}
}
//输出结果
//SPRING
//SUMMER
//AUTUMN
//WINTER
static 枚举类型[] values():返回枚举类型的对象数组。该方法可以很方便地遍历所有的枚举值，是一个静态方法

valueOf(String objName)

static 枚举类型 valueOf(String name)：可以把一个字符串转为对应的枚举类对象。要求字符串必须是枚举类对象的“名字”。如不是，会有运行时异常：IllegalArgumentException。public class SeasonTest{public static void main(String []args){String objName = "SPRING";Season season1 = Season.valueOf(objName);System.out.println(season1);	//SPRINGSeason season2 = Season.valueOf("WINTER");System.out.println(season2);	//WINTER}
}
//若重写了toSpring()方法，则按照重写后的来输出

int ordinal（）

public class SeasonTest{public static void main(String []args){System.out.println(Season.SPRING.ordinal());System.out.println(Season.SUMMER.ordinal());System.out.println(Season.AUTUMN.ordinal());System.out.println(Season.WINTER.ordinal());}
}
//int ordinal():返回当前枚举常量的次序号，默认从0开始
//输出结果 
//0
//1
//2
//3

枚举类实现接口操作

枚举类实现接口，在枚举类中重写接口中的抽象方法。当通过不同的枚举类对象调用此方法时，执行的是同一个方法

enum Season implements Info{SPRING("春天","春暖花开"),SUMMER("夏天","烈日炎炎"),AUTUMN("秋天","秋高气爽"),WINTER("冬天","白雪皑皑");private final String seasonName;	//季节名称private final String seasonDesc;	//季节描述private Season(String seasonName,String seasonDesc){this.seasonName = seasonName;this.seasonDesc = seasonDesc;}public String getSeasonName(){returtn this.seasonName;}public String getSeasonDesc(){return this.seasonName;}public void show(){System.out.println("这是一个季节");}
}
interface Info{void show();
}public class SeasonTest{public static void main(String []args){Season.SPRING.show();Season.SUMMER.show();}
}
//此时，重写方法是在Season类中
//输出结果:
// 这是一个季节
// 这是一个季节

让枚举类的每一个对象都重写接口中的抽象方法，当通过不同的枚举类对象调用此方法时，执行的是不同的方法

interface Info{void show();
}enum Season implements Info{SPRING("春天","春意盎然"){public void show(){System.out.println("春风又绿江南岸");}},SUMMER("夏天","烈日炎炎"){public void show(){System.out.println("映日荷花别样红");}},AUTUMN("秋天","秋高气爽"){public void show(){System.out.println("秋水共长天一色");}},WINTER("冬天","白雪皑皑"){public void show(){System.out.println("窗含西岭千秋雪");}};private final String seasonName;private final String seasonDesc;private Season(String seasonName,String seasonDesc){this.seasonName = seasonName;this.seasonDesc = seasonDesc;}public String getSeasonName(){return this.seasonName;}public String getSeasonDesc(){return this.seasonDesc;}}
public class SeasonTest{public static void main(String []args){Season []seasons = Season.values();for(int i = 0; i < seasons.length;i++){seasons[i].show();}}
}//输出
春风又绿江南岸
映日荷花别样红
秋水共长天一色
窗含西岭千秋雪