Java 第七章.枚举类

1.概述

1.类的对象是有限个的，确定的。我们称此类是枚举类

2.当需要定义一组常量时，强烈建议使用枚举类

3.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。

2.如何定义枚举类

方式一：jdk5.0之前，自定义枚举类

import com.sun.scenario.effect.impl.sw.sse.SSEBlend_SRC_OUTPeer;
import com.sun.xml.internal.ws.api.model.wsdl.WSDLOutput;

public class SeasonTest {
    public static void main(String[] args) {

        Season spring = Season.SPRING;
        System.out.println(spring);
        System.out.println(spring.toString());
        System.out.println(spring.getSeasonName());


    }

}
//自定义枚举类
class Season{
    //1.声明Season的对象的属性，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.seasonDesc = seasonDesc;
        this.seasonName = seasonName;
    }
    //3.提供当前枚举类的多个对象,public static final修饰
    public static final Season SPRING = new Season("春天","春暖花开");
    public static final Season SUMMER = new Season("夏天","热");
    public static final Season AUTUMN = new Season("秋天","分手");
    public static final Season WINTER = new Season("冬天","冷");
    //4.其他述求1.获取枚举类对象属性
    public String getSeasonDesc() {
        return seasonDesc;
    }

    public String getSeasonName() {
        return seasonName;
    }
    //4.其他述求1.提供toString()


    @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

定义的枚举类默认继承于java.lang.Enum类

public class SeasonTest1 {
    public static void main(String[] args) {
        Season1 spring = Season1.SPRING;
        System.out.println(spring);

    }
}
enum Season1{

    //1.提供当前枚举类的多个对象
    //格式： 对象名(形参列表),
    //说明：每句结尾后面用,最后一个有;
    SPRING("春天","春暖花开"),
    SUMMER("夏天","热"),
    AUTUMN("秋天","分手"),
    WINTER("冬天","冷");

    //2.声明Season的对象的属性，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.seasonDesc = seasonDesc;
        this.seasonName = seasonName;
    }

    //4.其他述求1.获取枚举类对象属性
    public String getSeasonDesc() {
        return seasonDesc;
    }

    public String getSeasonName() {
        return seasonName;
    }

    //4.其他述求1.提供toString()

    @Override
    public String toString() {
        return "Season1{" +
                "seasonName='" + seasonName + '\'' +
                ", seasonDesc='" + seasonDesc + '\'' +
                '}';
    }


}

3.Enum类中的常用方法

1. 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。

2. 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。 
（判断对象是否属于枚举类）

3. toString()：返回当前枚举类对象常量的名称

应用

public class SeasonTest1 {
    public static void main(String[] args) {
        //toString()
        Season1 spring = Season1.SPRING;
        System.out.println(spring);
        System.out.println("****************************");
        //Values()
        Season1[] val = Season1.values();
        for (int i = 0; i < val.length;i++){
            System.out.println(val[i]);
        }
        System.out.println("****************************");
        //valuesOf(String str)
        Season1 summer = Season1.valueOf("SUMMER");
        System.out.println(summer);

    }
}
enum Season1{

    //1.提供当前枚举类的多个对象
    //格式： 对象名(形参列表),
    //说明：每句结尾后面用,最后一个有;
    SPRING("春天","春暖花开"),
    SUMMER("夏天","热"),
    AUTUMN("秋天","分手"),
    WINTER("冬天","冷");

    //2.声明Season的对象的属性，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.seasonDesc = seasonDesc;
        this.seasonName = seasonName;
    }

    //4.其他述求1.获取枚举类对象属性
    public String getSeasonDesc() {
        return seasonDesc;
    }

    public String getSeasonName() {
        return seasonName;
    }



}

4.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

让枚举类中的对象分别实现抽象方法

举例

public class SeasonTest1 {
    public static void main(String[] args) {
        //toString()
        Season1 spring = Season1.SPRING;
        System.out.println(spring);
        System.out.println("****************************");
        //Values()
        Season1[] val = Season1.values();
        for (int i = 0; i < val.length;i++){
            System.out.println(val[i]);
            val[i].show();
        }
        System.out.println("****************************");
        //valuesOf(String str)
        Season1 summer = Season1.valueOf("SUMMER");
        System.out.println(summer);

        spring.show();

    }
}
interface info{
    void show();
}
enum Season1{

    //1.提供当前枚举类的多个对象
    //格式： 对象名(形参列表),
    //说明：每句结尾后面用,最后一个有;

    //情况二
    SPRING("春天","春暖花开"){
        public void show(){
            System.out.println("晴天");
        }
    },
    SUMMER("夏天","热"){
        public void show(){
            System.out.println("夏天");
        }
    },
    AUTUMN("秋天","分手"){
        public void show(){
            System.out.println("秋歌");
        }
    },
    WINTER("冬天","冷"){
        public void show(){
            System.out.println("大约在冬季");
        }
    };

    //2.声明Season的对象的属性，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.seasonDesc = seasonDesc;
        this.seasonName = seasonName;
    }

    //4.其他述求1.获取枚举类对象属性
    public String getSeasonDesc() {
        return seasonDesc;
    }

    public String getSeasonName() {
        return seasonName;
    }
    //情况一
    public void show(){
        System.out.println("奥里给");
    }



}