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：SPRING System.out.println(Season.SUMMER.toString()); //输出：SUMMER System.out.println(Season.AUTUMN.toString()); //输出：AUTUMN System.out.println(Season.WINTER.toString()); //输出：WINTER System.out.println(Season.SPRING); //输出：SPRING System.out.println(Season.SUMMER); //输出：SUMMER System.out.println(Season.AUTUMN); //输出: AUTUMN System.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); //SPRING Season 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