enum(枚举)类介绍🥥 🍑

java枚举类是一组预定义常量的集合，使用enum关键字声明这个类，常量名称官方建议大写

1.enum类基本用法

举一个常见的例子，例如星期就可以描述为一个枚举类，如下

java
public enum Day {
    SUNDAY, MONDAY, TUESDAY, WEDNESDAY,THURSDAY, FRIDAY, SATURDAY 
}

怎么调用呢，Java switch语句参数就支持enum类

java
public class EnumTest {
    Day day;
    
    public EnumTest(Day day) {
        this.day = day;
    }
    
    public void tellItLikeItIs() {
        switch (day) {
            case MONDAY:
                System.out.println("周一各种不在状态");
                break;
                    
            case FRIDAY:
                System.out.println("周五感觉还不错");
                break;
                         
            case SATURDAY: case SUNDAY:
                System.out.println("周末给人的感觉是最棒的");
                break;
                        
            default:
                System.out.println("周内感觉就那样吧。。。");
                break;
        }
    }
    
    public static void main(String[] args) {
        EnumTest firstDay = new EnumTest(Day.MONDAY);
        firstDay.tellItLikeItIs();
        EnumTest thirdDay = new EnumTest(Day.WEDNESDAY);
        thirdDay.tellItLikeItIs();
        EnumTest fifthDay = new EnumTest(Day.FRIDAY);
        fifthDay.tellItLikeItIs();
        EnumTest sixthDay = new EnumTest(Day.SATURDAY);
        sixthDay.tellItLikeItIs();
        EnumTest seventhDay = new EnumTest(Day.SUNDAY);
        seventhDay.tellItLikeItIs();
    }
}

运行结果

或者

通过名称获取对应的值

java
public enum ReturnEnum {
    patientSex("PATIENT_SEX"),
    submitTime("submit_Time"),
    submitDoctor("submit_Doctor"),
    deptDischargeName("dept_Discharge_Name"),
    returnCount("return_count"),
    dischargeTime("discharge_Time"),
    diagnosis("diagnosis");

    public String column;

     ReturnEnum(String  column) {
        this.column=column;
    }
    public String getColumn(){
        return column;
    }
    public static String getColumnByName(String column){
        for (ReturnEnum returnEnum:ReturnEnum.values()){
            if (returnEnum.name().equals(column)){
                return returnEnum.getColumn();
            }
        }
        return null;
    }

使用

System.out.println(ReturnEnum.getColumn("diagnosis"));

2.enum类和static常量区别

看了上面的例子，有些小伙伴就嗤之以鼻孔了，这没什么嘛，java静态常量也一样可以办到

java
public class EnumTest2 {
    public static final int MONDAY= 1;
    public static final int WEDNESDAY= 3;
    public static final int FRIDAY= 5;
    public static final int SATURDAY= 6;
    public static final int SUNDAY= 7;

    public void tellItLikeItIs(int day) {
        switch (day) {
            case 1:
                System.out.println("周一各种不在状态");
                break;

            case 5:
                System.out.println("周五感觉还不错");
                break;

            case 6: case 7:
                System.out.println("周末给人的感觉是最棒的");
                break;

            default:
                System.out.println("周内感觉就那样吧。。。");
                break;
        }
    }

    public static void main(String[] args) {
        EnumTest2 firstDay = new EnumTest2();
        firstDay.tellItLikeItIs(MONDAY);
        EnumTest2 thirdDay = new EnumTest2();
        thirdDay.tellItLikeItIs(WEDNESDAY);
        EnumTest2 fifthDay = new EnumTest2();
        fifthDay.tellItLikeItIs(FRIDAY);
        EnumTest2 sixthDay = new EnumTest2();
        sixthDay .tellItLikeItIs(SATURDAY);
        EnumTest2 seventhDay = new EnumTest2();
        seventhDay.tellItLikeItIs(SUNDAY);
    }
}

在这个使用方式效果上来看是没有区别的，其实enum类的每一个枚举值也是 static final的，但是我们为什么要选择使用enum枚举类呢 1.static方式的静态变量类型不安全，我们可以在调用的时候传入其他值，导致错误 例如： seventhDay.tellItLikeItIs(999); 2.static方式的静态变量不支持属性扩展，每一个key对应一个值，而enum的每一个key可以拥有自己的属性

3.enum类自定义属性

这就是enum比static静态变量好用的地方了，可以赋予每一个枚举值若干个属性，例如

java
public enum Day {
    MONDAY(1, "星期一", "星期一各种不在状态"),
    TUESDAY(2, "星期二", "星期二依旧犯困"),
    WEDNESDAY(3, "星期三", "星期三感觉半周终于过去了"),
    THURSDAY(4, "星期四", "星期四期待这星期五"),
    FRIDAY(5, "星期五", "星期五感觉还不错"),
    SATURDAY(6, "星期六", "星期六感觉非常好"),
    SUNDAY(7, "星期日", "星期日感觉周末还没过够。。。");

    Day(int index, String name, String value) {
        this.index = index;
        this.name = name;
        this.value = value;
    }

    private int index;
    private String name;
    private String value;

    public int getIndex() {
        return index;
    }

    public void setIndex(int index) {
        this.index = index;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getValue() {
        return value;
    }

    public void setValue(String value) {
        this.value = value;
    }
}

这次测试类就有些些变化了，更灵活了

java
public class EnumTest {
    Day day;

    public EnumTest(Day day) {
        this.day = day;
    }

    public void tellItLikeItIs() {
        switch (day) {
            case MONDAY:
                System.out.println(day.getName()+day.getValue());
                break;

            case FRIDAY:
                System.out.println(day.getName()+day.getValue());
                break;

            case SATURDAY: case SUNDAY:
                System.out.println(day.getName()+day.getValue());
                break;

            default:
                System.out.println(day.getName()+day.getValue());
                break;
        }
    }

    public static void main(String[] args) {
        EnumTest firstDay = new EnumTest(Day.MONDAY);
        firstDay.tellItLikeItIs();
        EnumTest thirdDay = new EnumTest(Day.WEDNESDAY);
        thirdDay.tellItLikeItIs();
        EnumTest fifthDay = new EnumTest(Day.FRIDAY);
        fifthDay.tellItLikeItIs();
        EnumTest sixthDay = new EnumTest(Day.SATURDAY);
        sixthDay.tellItLikeItIs();
        EnumTest seventhDay = new EnumTest(Day.SUNDAY);
        seventhDay.tellItLikeItIs();
    }
}

运行结果

4.enum类当成字典对照

public enum Day {
    MONDAY("星期一",1), TUESDAY("星期二",1), WEDNESDAY("星期三",1),THURSDAY("星期四",1), FRIDAY("星期五",1), SATURDAY("星期六",1), SUNDAY("星期日",1);

    private String dayName;
    private Integer dayNum;

    private Day(String dayName,Integer dayNum){
        this.dayName=dayName;
        this.dayNum=dayNum;
    }

    public static String getDayName(int dayNum){
        for (Day day:Day.values()){
            if (day.dayNum==dayNum){
                return day.getDayName();
            }
        }
        return null;
    }

    public static Integer getDayNum(String dayName){
        for (Day day:Day.values()){
            if (day.getDayName().equals(dayName)){
                return day.getDayNum();
            }
        }
        return null;
    }

    public String getDayName() {
        return dayName;
    }

    public void setDayName(String dayName) {
        this.dayName = dayName;
    }

    public Integer getDayNum() {
        return dayNum;
    }

    public void setDayNum(Integer dayNum) {
        this.dayNum = dayNum;
    }
}

测试类

public class EnumTest {

    public static void main(String[] args) {
        System.out.println(Day.getDayName(1));
        System.out.println(Day.getDayNum("星期二"));
    }

}

运行结果

5.enum类高级玩法

你以为enum这样就完了么，还有更好玩的东西，每一个enum枚举值还可以拥有各自的内部方法！二话不说，上栗子

java
public enum Day {
    MONDAY(1, "星期一", "各种不在状态"){
        @Override
        public Day getNext() {
            return TUESDAY;
        }
    },
    TUESDAY(2, "星期二", "依旧犯困"){
        @Override
        public Day getNext() {
            return WEDNESDAY;
        }
    },
    WEDNESDAY(3, "星期三", "感觉半周终于过去了"){
        @Override
        public Day getNext() {
            return THURSDAY;
        }
    },
    THURSDAY(4, "星期四", "期待这星期五"){
        @Override
        public Day getNext() {
            return FRIDAY;
        }
    },
    FRIDAY(5, "星期五", "感觉还不错"){
        @Override
        public Day getNext() {
            return SATURDAY;
        }
    },
    SATURDAY(6, "星期六", "感觉非常好"){
        @Override
        public Day getNext() {
            return SUNDAY;
        }
    },
    SUNDAY(7, "星期日", "感觉周末还没过够。。。"){
        @Override
        public Day getNext() {
            return MONDAY;
        }
    };

    Day(int index, String name, String value) {
        this.index = index;
        this.name = name;
        this.value = value;
    }

    private int index;
    private String name;
    private String value;
    public abstract Day getNext();

    public int getIndex() {
        return index;
    }

    public void setIndex(int index) {
        this.index = index;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getValue() {
        return value;
    }

    public void setValue(String value) {
        this.value = value;
    }

}

调用下看看

java
public class EnumTest {
    Day day;

    public EnumTest(Day day) {
        this.day = day;
    }

    public void tellItLikeItIs() {
        switch (day) {
            case MONDAY:
                System.out.println(day.getName()+day.getValue());
                System.out.println(day.getName()+"的下一天是"+day.getNext().getName());
                break;

            case FRIDAY:
                System.out.println(day.getName()+day.getValue());
                System.out.println(day.getName()+"的下一天是"+day.getNext().getName());
                break;

            case SATURDAY: case SUNDAY:
                System.out.println(day.getName()+day.getValue());
                System.out.println(day.getName()+"的下一天是"+day.getNext().getName());
                break;

            default:
                System.out.println(day.getName()+day.getValue());
                System.out.println(day.getName()+"的下一天是"+day.getNext().getName());
                break;
        }
    }

    public static void main(String[] args) {
        EnumTest firstDay = new EnumTest(Day.MONDAY);
        firstDay.tellItLikeItIs();
        EnumTest thirdDay = new EnumTest(Day.WEDNESDAY);
        thirdDay.tellItLikeItIs();
        EnumTest fifthDay = new EnumTest(Day.FRIDAY);
        fifthDay.tellItLikeItIs();
        EnumTest sixthDay = new EnumTest(Day.SATURDAY);
        sixthDay.tellItLikeItIs();
        EnumTest seventhDay = new EnumTest(Day.SUNDAY);
        seventhDay.tellItLikeItIs();
    }
}

运行结果