Java基础系列（11）- 枚举类

枚举类的使用：入门

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. 如果枚举类中只有一个对象，则可以作为单例模式的实现方式

比如：星期、季节等

定义枚举类

自定义枚举类

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

class Season{
    //1.声明Season对象的属性：private final修饰
    private final String seasonName;
    private final String seasonDese;

    //2.私有化类的构造器，并给对象属性赋值
    private Season(String seasonName, String seasonDese){
        this.seasonName = seasonName;
        this.seasonDese = seasonDese;
    }

    //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", "热死了");
    public static final Season AUTUMN = new Season("秋天","秋高气爽");
    public static final Season WINTER = new Season("冬天","冷死了");

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

    public String getSeasonDese() {
        return seasonDese;
    }

    //4.其他诉求1：提供toString()


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

使用enum关键字定义（JDK1.6）

说明：定义的枚举类默认继承于Java.lang.Enum类

public class SeasonTest{
    public static void main(String[] args) {
        Season spring = Season.SPRING;
        System.out.println(spring); //SPRING
        System.out.println(Season.class.getSuperclass());  //class java.lang.Enum
    }
}

enum Season {
    //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", "热死了"),
    AUTUMN("秋天", "秋高气爽"),
    WINTER("冬天", "冷死了");

    //2.声明Season对象的属性：private final修饰
    private final String seasonName;
    private final String seasonDese;

    //3.私有化类的构造器，并给对象属性赋值
    private Season(String seasonName, String seasonDese) {
        this.seasonName = seasonName;
        this.seasonDese = seasonDese;
    }

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

    public String getSeasonDese() {
        return seasonDese;
    }

}

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 SeasonTest{
    public static void main(String[] args) {
        Season spring = Season.SPRING;
        System.out.println(spring); //SPRING

        //values()
        Season[] values = Season.values();
        for (int i = 0; i < values.length; i++) {
            System.out.println(values[i]);  //SPRING/SUMMER/AUTUMN/WINTER
        }

        //valueOf(String objName):
        Season winter = Season.valueOf("WINTER");
        System.out.println(winter); //WINTER
    }
}

enum Season {
    //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", "热死了"),
    AUTUMN("秋天", "秋高气爽"),
    WINTER("冬天", "冷死了");

    //2.声明Season对象的属性：private final修饰
    private final String seasonName;
    private final String seasonDese;

    //3.私有化类的构造器，并给对象属性赋值
    private Season(String seasonName, String seasonDese) {
        this.seasonName = seasonName;
        this.seasonDese = seasonDese;
    }

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

    public String getSeasonDese() {
        return seasonDese;
    }

}

使用enum关键字定义的枚举类实现接口

情况一：实现接口，在enum类中实现抽象方法

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

        //values()
        Season[] values = Season.values();
        for (int i = 0; i < values.length; i++) {
            System.out.println(values[i]);  //SPRING/SUMMER/AUTUMN/WINTER
        }

        //valueOf(String objName):
        Season winter = Season.valueOf("WINTER");
        System.out.println(winter); //WINTER
        winter.show();
    }
}

interface Info{
    void show();
}

enum Season 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"),
    SUMMER("夏天", "热死了"),
    AUTUMN("秋天", "秋高气爽"),
    WINTER("冬天", "冷死了");

    //2.声明Season对象的属性：private final修饰
    private final String seasonName;
    private final String seasonDese;

    //3.私有化类的构造器，并给对象属性赋值
    private Season(String seasonName, String seasonDese) {
        this.seasonName = seasonName;
        this.seasonDese = seasonDese;
    }

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

    public String getSeasonDese() {
        return seasonDese;
    }

    @Override
    public void show() {
        System.out.println("这是一个季节!");
    }
}

情况二：让枚举类的对象分别实现接口中的抽象方法

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

        //values()
        Season[] values = Season.values();
        for (int i = 0; i < values.length; i++) {
            System.out.println(values[i]);  //SPRING/SUMMER/AUTUMN/WINTER
        }

        //valueOf(String objName):
        Season winter = Season.valueOf("WINTER");
        System.out.println(winter); //WINTER
        winter.show();
    }
}

interface Info{
    void show();
}

enum Season 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");
        }
    },
    SUMMER("夏天", "热死了"){
        @Override
        public void show() {
            System.out.println("夏天");
        }
    },
    AUTUMN("秋天", "秋高气爽"){
        @Override
        public void show() {
            System.out.println("秋天");
        }
    },
    WINTER("冬天", "冷死了"){
        @Override
        public void show() {
            System.out.println("冬天");
        }
    };

    //2.声明Season对象的属性：private final修饰
    private final String seasonName;
    private final String seasonDese;

    //3.私有化类的构造器，并给对象属性赋值
    private Season(String seasonName, String seasonDese) {
        this.seasonName = seasonName;
        this.seasonDese = seasonDese;
    }

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

    public String getSeasonDese() {
        return seasonDese;
    }

}