枚举基础

枚举定义

• 枚举类里的值必须是有限个的，确定的。
• 枚举类是一组常量。
• 如果枚举类只有一个对象，则可以作为一个单例的实现方式。

代码示例

JDK1.5之前的写法

//自定义枚举类——JDK1.5之前
public class SeasonEnum {
    //1、声明枚举类属性为 private final 防止属性变量被改变
    private final int seasonValue;
    private final String seasonName;

    //2、私有化构造器，防止被创建新的枚举，因为枚举的常量是固定数量的
    //并给对象属性赋值
    private SeasonEnum(int seasonValue, String seasonName){
        this.seasonValue = seasonValue;
        this.seasonName = seasonName;
    }
    //3、声明具体的枚举常量，对外提供使用
    public static final SeasonEnum SPRING = new SeasonEnum(1,"SPRING");
    public static final SeasonEnum SUMMER = new SeasonEnum(2,"SUMMER");
    public static final SeasonEnum AUTUMN = new SeasonEnum(3,"AUTUMN");
    public static final SeasonEnum WINTER = new SeasonEnum(4,"WINTER");

    //4、提供枚举类对象属性的访问
    public int getSeasonValue() {
        return seasonValue;
    }
    public String getSeasonName() {
        return seasonName;
    }
    //5、提供toString()

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

JDK1.5及之后的写法

/**
 * JDK5创建枚举
 * enum关键字创建的枚举类继承于java.lang.Enum，可以通过getParentClass确定
 */
public enum NewSeasonEnum {
    //1、枚举对象必须声明在最前面
    SPRING(1, "SPRING"),
    SUMMER(2, "SUMMER"),
    AUTOMN(3, "AUTOMN"),
    WINTER(4, "WINTER");
    //2、定义枚举属性
    private final int index;
    private final String name;

    //3、私有化构造器，避免被实例化
    NewSeasonEnum(int index, String name) {
        this.index = index;
        this.name = name;
    }

    //4、提供属性get方法
    public int getIndex() {
        return index;
    }

    public String getName() {
        return name;
    }

    //5、根据index获取枚举对象
    public static NewSeasonEnum get(int index) {
        for (NewSeasonEnum e : NewSeasonEnum.values()) {
            if (e.getIndex() == index) {
                return e;
            }
        }
        return null;
    }

    //6、根据index获取枚举对象名
    public static String getNameByIndex(int index) {
        NewSeasonEnum node = get(index);
        return node == null ? null : node.getName();
    }
    //7、如果需要不只是打印枚举对象名称，则可以重写toString方法

}

public class EnumTest {
    @Test
    public void test(){
        System.out.println(SeasonEnum.AUTUMN);
        //SeasonEnum{seasonValue=3, seasonName='AUTUMN'}
        System.out.println(NewSeasonEnum.SUMMER);
        //SUMMER
    }

    @Test
    public void test2(){
        DifferenceSeasonEnum.AUTOMN.show();
        DifferenceSeasonEnum.SPRING.show();
        //AUTOMN SHOW
        //SPRING SHOW
    }
}

枚举类实现接口展示不同的表现写法

//让枚举类的对象分别实现接口中的方法，体现出不同的枚举有不同的表现
public enum DifferenceSeasonEnum implements IShow {
    //1、枚举对象必须声明在最前面
    SPRING(1, "SPRING") {
        @Override
        public void show() {
            System.out.println("SPRING SHOW");
        }
    },
    SUMMER(2, "SUMMER"){
        @Override
        public void show() {
            System.out.println("SUMMER SHOW");
        }
    },
    AUTOMN(3, "AUTOMN"){
        @Override
        public void show() {
            System.out.println("AUTOMN SHOW");
        }
    },
    WINTER(4, "WINTER"){
        @Override
        public void show() {
            System.out.println("WINTER SHOW");
        }
    };
    //2、定义枚举属性
    private final int index;
    private final String name;

    //3、私有化构造器，避免被实例化
    DifferenceSeasonEnum(int index, String name) {
        this.index = index;
        this.name = name;
    }

    //4、提供属性get方法
    public int getIndex() {
        return index;
    }

    public String getName() {
        return name;
    }
}

public interface IShow {
    void show();
}

参考

Java入门视频教程

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