一、枚举类的使用
- 枚举类的理解:类的对象只有有限个,确定的。我们称此类为枚举类
- 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,则可以作为单例模式的实现方式。
二、如何定义枚举类
方式一:jdk5.0之前,自定义枚举类
/**
*
* 自定义枚举类
*
*/
public class test01 {
public static void main(String[] args) {
Season spring = Season.SPRING;
System.out.println(spring);
}
}
//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;
}
//3.提供当前枚举类的多个对象:public static final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");
//4.其他诉求:获取枚举类对象的属性
public String getSeasonName(){
return seasonName;
}
public String getSeasonDesc(){
return seasonDesc;
}
@Override
public String toString() {
return "Season{" +
"seasonName='" + seasonName + '\'' +
", seasonDesc='" + seasonDesc + '\'' +
'}';
}
}
方式二:jdk5.0,可以使用enum关键字定义枚举类
/**
*
* 使用enum关键字定义枚举类
* 说明:定义的枚举类默认继承于java.lang.Enum类
*
*/
public class test02 {
public static void main(String[] args) {
Season2 summer = Season2.SUMMER;
System.out.println(summer);
System.out.println(Season.class.getSuperclass());
}
}
//使用enum关键字
enum Season2{
//1.提供当前枚举类的对象,多个对象之间用","隔开,末尾对象";"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;
}
//4.其他诉求
public String getSeasonName(){
return seasonName;
}
public String getSeasonDesc(){
return seasonDesc;
}
}
三、Enum类中常用的方法:
- 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 枚举值。
- valueOf(String str):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。
- toString():返回当前枚举类对象常量的名称
public class test03 {
public static void main(String[] args) {
Season3 summer = Season3.SUMMER;
//toString
System.out.println(summer.toString());
System.out.println("***************");
//values()
Season3[] values = Season3.values();
for(int i = 0; i < values.length; i++){
System.out.println(values[i]);
}
Thread.State[] values2 = Thread.State.values();
for(int i = 0; i < values2.length; i++){
System.out.println(values2[i]);
}
System.out.println("***************");
//valueOf(String objName) 如果没找到会报异常
Season3 winter = Season3.valueOf("WINTER");
System.out.println(winter);
}
}
enum Season3{
//1.提供当前枚举类的对象,多个对象之间用","隔开,末尾对象";"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.私有类的构造器,并给对象属性赋值
private Season3(String seasonName, String seasonDesc){
this.seasonName = seasonName;
this.seasonDesc = seasonDesc;
}
//4.其他诉求
public String getSeasonName(){
return seasonName;
}
public String getSeasonDesc(){
return seasonDesc;
}
}
四、使用enum关键字定义的枚举类实现接口的情况
/**
*
* 情况一:实现接口,在enum类中实现抽象方法
* 情况二:让枚举类的对象分别实现接口中的方法
*
*/
public class test04 {
public static void main(String[] args) {
Season4 winter = Season4.WINTER;
winter.show();
}
}
interface Info{
void show();
}
enum Season4 implements Info{
//1.提供当前枚举类的对象,多个对象之间用","隔开,末尾对象";"结束
SPRING("春天", "春暖花开"){
@Override
public void show() {
System.out.println("春天在哪里?");
}
},
SUMMER("夏天", "夏日炎炎"){
@Override
public void show() {
System.out.println("宁夏");
}
},
AUTUMN("秋天", "秋高气爽"){
@Override
public void show() {
System.out.println("秋天不回来");
}
},
WINTER("冬天", "冰天雪地"){
@Override
public void show() {
System.out.println("大学在冬季");
}
};
//2.声明Season对象的属性:private final修饰
private final String seasonName;
private final String seasonDesc;
//3.私有类的构造器,并给对象属性赋值
private Season4(String seasonName, String seasonDesc){
this.seasonName = seasonName;
this.seasonDesc = seasonDesc;
}
//4.其他诉求
public String getSeasonName(){
return seasonName;
}
public String getSeasonDesc(){
return seasonDesc;
}
// @Override
// public void show() {
// System.out.println("这是一个季节");
// }
}
来源:https://www.cnblogs.com/xiaoran991/p/12552619.html