枚举类

枚举类的说明

1. 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
2. 当需要定义一组常量时，强烈建议使用枚举类
3. 如果枚举类中只一个对象，则可以作为单例模式的实现方式。

回顾单例模式的创建

饿汉式

class Bank {
    //1.私化类的构造器
    private Bank() {

    }
    //2.内部创建类的对象
    //3.要求此对象也必须声明为静态的
    private static Bank instance = new Bank();

    //4.提供公共的静态的方法，返回类的对象
    public static Bank getInstance() {
        return instance;
    }
}

懒汉式

class Bank {

    private Bank() {

    }
    private static Bank instance = null;
    public static Bank getInstance() {
        if (instance == null) {
            synchronized (Bank.class) {
                if (instance == null) {
                    instance = new Bank();
                }
            }
        }
        return instance;
    }
}

单例模式作为特殊的枚举类出现，其他枚举类的创建方式也类似

自定义枚举类的创建

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1：获取枚举类对象的属性
    public String getSeasonName() {
        return seasonName;
    }

    public String getSeasonDesc() {
        return seasonDesc;
    }

    //4.其他诉求1：提供toString()
    @Override
    public String toString() {
        return "Season{" +
                "seasonName='" + seasonName + '\'' +
                ", seasonDesc='" + seasonDesc + '\'' +
                '}';
    }
}
public class SeasonTest {
    public static void main(String[] args) {
        System.out.println(Season.SPRING);//Season{seasonName='春天', seasonDesc='春暖花开'}
        System.out.println(Season.SPRING.getSeasonDesc());//春暖花开
        System.out.println(Season.SUMMER.getSeasonName());//夏天
    }
}

使用enum关键字创建枚举类

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";"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;

    //2.私化类的构造器,并给对象属性赋值

    private Season1(String seasonName, String seasonDesc) {
        this.seasonName = seasonName;
        this.seasonDesc = seasonDesc;
    }

    //4.其他诉求1：获取枚举类对象的属性
    public String getSeasonName() {
        return seasonName;
    }

    public String getSeasonDesc() {
        return seasonDesc;
    }

}
public class SeasonTest1 {
    public static void main(String[] args) {
        System.out.println(Season1.SPRING);//SPRING
        System.out.println(Season.AUTUMN.getSeasonName());//秋天
        System.out.println(Season.WINTER.getSeasonDesc());//冰天雪地
    }
}

说明：

• enum定义枚举类与自定义枚举类步骤差不多。需要将提供当前枚举类的对象步骤放在第一步
• 使用enum定义枚举类之后，继承于java.lang.Enum类，里面重写了toString方法，一般不用在对toString方法进行重写

Enum类的主要方法

• 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3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

values()

        Season1[] season1 = Season1.values();
        for (int i = 0; i < season1.length; i++) {
            System.out.println("season1[" + i + "] = " + season1[i]);
//            season1[0] = SPRING
//            season1[1] = SUMMER
//            season1[2] = AUTUMN
//            season1[3] = WINTER
        }

valueOf(String objName)

        Season1 winter = Season1.valueOf("WINTER");//如果没objName的枚举类对象，则抛异常
        System.out.println(winter);//WINTER

使用enum定义枚举类之后，如何让枚举类对象分别实现接口

interface Info {
    void show();
}

//使用enum关键字枚举类
enum Season1 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");
        }
    };

	Season1.SPRING.show();//春天在哪里？