枚举类的使用
1.简介:
类的对象只有有限个,确定的,我们称之为枚举类。
例如 星期,线程状态,性别,季节等。
当需要定义一组常量时,强烈建议使用枚举类
如果枚举类中只有一个对象,则可以作为一个单例模式的实现方式
2.如何定义枚举类
方式一:jdk 1.5 之前,自定义枚举类
//自定义枚举类 class Season{ //1.声明Season对象的属性:private final 修饰 private final String seasonName; private final String seasonDesc; //2.私有化类的构造器,并给对象属性赋值 private Season(String seasonName,String seasonDesc){ this.seasonName = seasonName; this.seasonDesc = seasonDesc; } public String getSeasonName() { return seasonName; } public String getSeasonDesc() { return seasonDesc; } @Override public String toString() { return "Season{" + "seasonName='" + seasonName + '\'' + ", seasonDesc='" + seasonDesc + '\'' + '}'; } //3.提供当前枚举类的多个对象 public static final 修饰的 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","冰天雪地"); }
对定义的枚举类进行测试:
public class SeasonTest { public static void main(String[] args){ Season season = Season.AUTUMN; System.out.println(season); //Season{seasonName='秋天', seasonDesc='秋高气爽'} } }
方式二:jdk1.5 以后,可以使用enum关键字定义枚举类
//使用enum关键字定义枚举类 enum Season1 { //1.提供当前枚举类的对象 多个对象之间用","隔开,末尾对象用“;”结束 SPRING ("春天", "春暖花开"), SUMMER ("夏天", "夏日炎炎"), AUTUMN ("秋天", "秋高气爽"), WINTER ("冬天", "冰天雪地"); //2.声明Season对象的属性:private final 修饰 private final String seasonName; private final String seasonDesc; //3.私有化类的构造器,并给对象属性赋值 private Season1(String seasonName, String seasonDesc) { this.seasonName = seasonName; this.seasonDesc = seasonDesc; } public String getSeasonName() { return seasonName; } public String getSeasonDesc() { return seasonDesc; } }
对使用enum关键字定义的枚举类进行测试:
public class SeasonTest2 { public static void main(String[] args) { Season2 summer=Season2.SUMMER; System.out.println(summer); //SUMMER }
3.Enum类中的常用方法
values()方法: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类
valueOf(String str)方法:可以把一个字符串转化为对应的枚举类对象,要求字符串必须是枚举类对象
toString()方法:返回当前枚举类对象常量的名称
public class SeasonTest1 { public static void main(String[] args) { Season1 summer=Season1.SUMMER; System.out.println(summer); //toString(): System.out.println(summer.toString()); /* 打印结果为: SUMMER SUMMER */ //values() System.out.println("******************"); Season1[] values = Season1.values(); for(int i=0;i<values.length;i++){ System.out.println(values[i]); /* 打印结果为: SPRING SUMMER AUTUMN WINTER */ } System.out.println("******************"); Thread.State[] values1 = Thread.State.values(); for(int i=0;i<values1.length;i++){ System.out.println(values1[i]); /* 打印结果为: NEW RUNNABLE BLOCKED WAITING TIMED_WAITING TERMINATED */ } //valueOf(String str) 返回枚举类中对象名为objName的对象, // 如果没有objName的枚举类对象,则抛异常 System.out.println("*****************#"); Season1 winter = Season1.valueOf("WINTER"); System.out.println(winter); /* 打印结果为: WINTER */ } }
4.使用enum关键字定义的枚举类实现接口的情况
1.实现接口,在enum类中实现抽象方法
2.让枚举类的对象分别实现接口中的抽象方法
接口类MessageInfo:
interface MessageInfo{ void show(); }
定义的枚举类实现上述接口:
//使用enum关键字定义枚举类 enum Season2 implements MessageInfo { //1.提供当前枚举类的对象 多个对象之间用","隔开,末尾对象用“;”结束 SPRING ("春天", "春暖花开"){ @Override public void show() { System.out.println("春天"); } }, SUMMER ("夏天", "夏日炎炎"){ @Override public void show() { System.out.println("夏天"); } }, AUTUMN ("秋天", "秋高气爽"){ @Override public void show() { System.out.println("秋天"); } }, WINTER ("冬天", "冰天雪地"){ @Override public void show() { System.out.println("冬天"); } }; //2.声明Season对象的属性:private final 修饰 private final String seasonName; private final String seasonDesc; //3.私有化类的构造器,并给对象属性赋值 private Season2(String seasonName, String seasonDesc) { this.seasonName = seasonName; this.seasonDesc = seasonDesc; } public String getSeasonName() { return seasonName; } public String getSeasonDesc() { return seasonDesc; } }
对其进行测试:
public class SeasonTest2 { public static void main(String[] args) { Season2 summer=Season2.SUMMER; System.out.println(summer); /* 打印结果为: SUMMER */ //values() Season2[] values = Season2.values(); for(int i=0;i<values.length;i++){ System.out.println(values[i]); values[i].show(); /* 打印结果为: SPRING 春天 SUMMER 夏天 AUTUMN 秋天 WINTER 冬天 */ } //valueOf(String str) 返回枚举类中对象名为objName的对象, // 如果没有objName的枚举类对象,则抛异常 System.out.println("*****************#"); Season2 winter = Season2.valueOf("WINTER"); System.out.println(winter); winter.show(); /* 打印结果为: WINTER 冬天 */ } }
作 者:sweetheart1998
出 处:https://home.cnblogs.com/u/gujun1998/
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