JAVA_基础枚举类

枚举类的理解

1）类的对象只有有限个，确定的。
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。

如何定义枚举类

方式一：JDK5.0之前，自定义枚举类。

public class SeasonTest {
    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","白雪皑皑");
    //4.其它诉求：获取枚举类对象的属性
    public String getSeasonName() {
        return seasonName;
    }
    public String getSeasonDesc() {
        return seasonDesc;
    }
    //5.其它诉求：提供toString方法
    @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。

1）定义的枚举类默认继承于java.lang.Enum类。
2）可以省去public final static Season = new Season。

public class SeasonenumTest {
    public static void main(String[] args) {
        Season1 season1 = Season1.AUTUMN;
        System.out.println(season1);
        System.out.println(Season1.class.getSuperclass());
    }
}
enum Season1 {
    //1.提供当前枚举类的多个对象,多个对象之间用逗号隔开，末尾用分号结束。
    SPRING("春天","春暖花开"),
    SUMMER("夏天","夏日炎炎"),
    AUTUMN("秋天","秋高气爽"),
    WINTER("冬天","白雪皑皑");
    //2.声明Season对象的属性：private final修饰
    private final String seasonDesc;
    private final String seasonName;
    //3.私有化类的构造器，并给对象赋值
    private Season1(String seasonName, String seasonDesc) {
        this.seasonName = seasonName;
        this.seasonDesc = seasonDesc;
    }
    //4.其它诉求：获取枚举类对象的属性
    public String getSeasonName() {
        return seasonName;
    }
    public String getSeasonDesc() {
        return seasonDesc;
    }
}

Enum类的主要方法

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。
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 SeasonenumTest {
    public static void main(String[] args) {
        Season1 season1 = Season1.AUTUMN;
        //toString()
        System.out.println(season1.toString());
        System.out.println(Season1.class.getSuperclass());
        System.out.println("***********************");
        //values()
        Season1[] values = Season1.values();
        for(int i = 0; i < values.length; i++) {
            System.out.println(values[i]);
        }
        System.out.println("***********************");
        Thread.State[] values1 = Thread.State.values();
        for (int i = 0; i < values1.length; i++) {
            System.out.println(values1[i]);
        }
        //valuesOf(String objName)：返回枚举类中对象名是objName的对象。
        //如果没有objName的枚举类对象，则抛异常：IllegalArgumentException
        Season1 winter = Season1.valueOf("WINTER");
        System.out.println(winter);
    }
}
enum Season1 {
    //1.提供当前枚举类的多个对象,多个对象之间用逗号隔开，末尾用分号结束。
    SPRING("春天","春暖花开"),
    SUMMER("夏天","夏日炎炎"),
    AUTUMN("秋天","秋高气爽"),
    WINTER("冬天","白雪皑皑");
    //2.声明Season对象的属性：private final修饰
    private final String seasonDesc;
    private final String seasonName;
    //3.私有化类的构造器，并给对象赋值
    private Season1(String seasonName, String seasonDesc) {
        this.seasonName = seasonName;
        this.seasonDesc = seasonDesc;
    }
    //4.其它诉求：获取枚举类对象的属性
    public String getSeasonName() {
        return seasonName;
    }
    public String getSeasonDesc() {
        return seasonDesc;
    }
}

使用enum关键字定义的枚举类实现接口的情况

1）情况一：实现接口，在enum类中实现抽象方法。
2）情况二：让枚举的对象分别实现接口中的抽象方法。