枚举类的使用
枚举类的理解
-
类的对象只有有限个，确定的。举例如下：
- 星期：Monday(星期一)、 …、 Sunday(星期天)
- 性别：Man(男)、Weman(女)
- 季节：Spring(春天)、 …、 Winter(冬天)
- 支付方式：Cash(现金)、WeChatPay(微信)、AliPay(支付宝)、BankCard(银行卡)、CreditCard(信用卡)
- 就职状态：Busy、Free、Vocation、Dimission
- 订单状态：Nonpayment(未付款)、Paid(已付款)、Delivered(已发货)、Return(退货)、Checked(已确认)Fulfilled(已配货)
- 线程状态：创建、就绪、运行、阻塞、死亡
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当需要定义一组常量时，强烈建议使用枚举类
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枚举类的实现
- jdk1.5之前需要自定义枚举类
- jdk1.5新增的enum关键字用于定义枚举类
-
若枚举只有一个对象，则可以作为一种单例模式的实现方式
自定义枚举类
枚举类的属性
- 枚举类对象的属性不应允许被改动，所以需要用private final来修饰
- 枚举类的使用private final修饰的属性应在构造器中为其赋值
- 若枚举类显示定义了带参数的构造器，则在列出枚举值的时也必须传入对应的参数
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| public class SeasonTest {
public static void main(String[] args) {
Season spring = Season.SPRING;
Season summer = Season.SUMMER;
Season autumn = Season.AUTUMN;
Season winter = Season.WINTER;
System.out.println(spring);
System.out.println(summer);
System.out.println(autumn);
System.out.println(winter);
}
}
class Season{
private final String seasonName;
private final String seasonDesc;
private Season(String seasonName,String seasonDesc){
this.seasonName=seasonName;
this.seasonDesc=seasonDesc;
}
public static final Season SPRING =new Season("春天","春暖花开");
public static final Season SUMMER =new Season("夏天","烈日炎炎");
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");
public String getSeasonName() {
return seasonName;
}
public String getSeasonDesc() {
return seasonDesc;
}
@Override
public String toString() {
return "enumText.Season{" +
"seasonName='" + seasonName + '\'' +
", seasonDesc='" + seasonDesc + '\'' +
'}';
}
}
|
使用enum关键字定义枚举类
使用说明
- 使用enum定义的枚举类默认继承了java.lang.Enum类，因此不能再继承其他类
- 枚举类的构造器只能用private权限修饰符
- 枚举类的所有实例必须在枚举类中显示列出，以",“分隔，”;"结尾。列出的实例系统会自动添加public static final修饰
- 必须在枚举类的首行声明枚举类对象
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| public class SeasonTest1 {
public static void main(String[] args) {
Season1 summer = Season1.SUMMER;
System.out.println(summer);
System.out.println(Season1.class.getSuperclass());
}
}
enum Season1 {
SPRING("春天", "春暖花开"),
SUMMER("夏天", "烈日炎炎"),
ANTUMN("秋天", "秋高气爽"),
WINTER("冬天", "冰天雪地");
private final String seasonName;
private final String seasonDesc;
Season1(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 "Season1{" +
"seasonName='" + seasonName + '\'' +
", seasonDesc='" + seasonDesc + '\'' +
'}';
}
}
|
注；Enum已经重写过toString()方法了 --> 得到当前枚举类常量的名称。
我们可以再次重写toString()方法，使得到的结果更易读
Enum类中的常用方法
| 方法 |
描述 |
| values() |
返回枚举类型的对象数组。该方法可以很方便的遍历所有枚举值 |
| valueOf(String objName) |
返回枚举类中对象名是objName的对象 |
| toString() |
返回当前枚举类对象常量的名称 如果没有objName的枚举类对象，则抛异常IllegalArgumentException |
values()和toString()方法测试
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| @Test
public void test01() {
Thread.State[] threads = Thread.State.values();
for (int i = 0; i < threads.length; i++) {
System.out.println(threads[i].toString());
}
}
|
valuesOf(String name)方法测试
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| @Test
public void test02(){
Season1 winter = Season1.valueOf("WINTER");
System.out.println(winter);
}
|
使用enum关键字定义枚举类实现接口
使用enum关键字定义的枚举类实现接口的情况
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| @Test
public void test03() {
Sex[] sexes = Sex.values();
for (int i = 0; i < sexes.length; i++) {
System.out.println(sexes[i]);
sexes[i].show();
}
}
interface Info {
void show();
}
enum Sex implements Info {
MAN("男人", "声音粗犷"),
WEMAN("女人", "声音细腻");
private final String sex;
private final String sound;
Sex(String sex, String sound) {
this.sex = sex;
this.sound = sound;
}
public String getSex() {
return sex;
}
@Override
public void show() {
System.out.println("这是一个性别");
}
}
|
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| @Test
public void test04(){
Season1[] season = Season1.values();
for (int i = 0; i < season.length; i++) {
System.out.println(season[i]);
season[i].show();
}
}
enum Season1 implements Info{
SPRING("春天", "春暖花开"){
@Override
public void show() {
System.out.println("这是春天，大地复苏");
}
},
SUMMER("夏天", "烈日炎炎"){
@Override
public void show() {
System.out.println("这是夏天，热得要死");
}
},
ANTUMN("秋天", "秋高气爽"){
@Override
public void show() {
System.out.println("这是秋天，硕果累累");
}
},
WINTER("冬天", "冰天雪地"){
@Override
public void show() {
System.out.println("这是冬天，白雪皑皑");
}
};
private final String seasonName;
private final String seasonDesc;
Season1(String seasonName, String seasonDesc) {
this.seasonName = seasonName;
this.seasonDesc = seasonDesc;
}
public String getSeasonName() {
return seasonName;
}
public String getSeasonDesc() {
return seasonDesc;
}
}
|
注解的使用
继续挖坑，以后再填
注解的理解
Annotation的使用示例
如何自定义注解
jdk中四个基本元注解的使用
利用反射获取注解信息
jdk8新特性：可重复注解
jkd8新特性：类型注解
