Detailed introduction to the use of enumerations in java-XML/RSS Tutorial-php.cn

Detailed introduction to the use of enumerations in java

黄舟

Release： 2016-12-19 14:23:35

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Enumeration features

1. Using enum to define an enumeration class inherits the java.lang.Enum class by default instead of inheriting the Object class. Among them, the java.lang.Enum class implements two interfaces, java.lang.Serializable and java.lang.Comparable

2. The constructor of the enumeration class can only use the private access modifier, if the access control of its constructor is omitted symbol, the private modification is used by default;

3. All instances of the enumeration class must be explicitly listed in the enumeration class, otherwise this enumeration class will never be able to generate instances. When these instances are listed, the system automatically adds public static final modifications without the need for programmers to add them explicitly.

public enum Week {
    MON{
        public String toLocaleString(){
            return "星期一";
        }
    },TUES{
        public String toLocaleString(){
            return "星期二";
        }
    },WEB{
        public String toLocaleString(){
            return "星期三";
        }

    },THUR{
        public String toLocaleString(){
            return "星期四";
        }

    },FRI{
        public String toLocaleString(){
            return "星期五";
        }

    },SAT{
        public String toLocaleString(){
            return "星期六";
        }

    },SUN{
        public String toLocaleString(){
            return "星期日";
        }

    };
    public abstract String toLocaleString();
}

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Traversal of enumerations

public class EnumTest {
    public static void main(String[] args){
        for(Week w:Week.values()){
            System.out.println(w);
        }
    }
}

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Common methods of enumerations

int compareTo method

String name() returns the name of the enumeration instance

int ordinal() returns the enumeration value in the enumeration Index

String toString() returns the instance name of the enumeration which is more commonly used than name

public static valueOf()

public class EnumTest {
    public static void main(String[] args){
        Week day =Week.FRI;
        System.out.println(day);//FRI
        System.out.println(day.name());//FRI
        System.out.println(day.ordinal());//4
        System.out.println(Week.valueOf("SUN").toLocaleString());//星期日
        System.out.println(Week.values().length);//7  获取枚举长度
    }
}

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Constructor of the enumeration

public enum Gender {
    MALE("男"),FEMALE("女");
    private String name;
    private Gender(String name){
        this.name =name;
    }
    public String getName(){
        return this.name;
    }
    public String toString(){
        String name = null;
        switch(this){
        case MALE:
            name="男";
            break;
        case FEMALE:
            name="女";
            break;
        }
        return name;
    }

}

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Comprehensive application example of the enumeration: traffic light

Detailed introduction to the use of enumerations in java

public enum Lamp {
     /*每个枚举元素各表示一个方向的控制灯*/    
     S2N("N2S","S2W",false),S2W("N2E","E2W",false),E2W("W2E","E2S",false),E2S("W2N","S2N",false),
     /*下面元素表示与上面的元素的相反方向的灯，它们的“相反方向灯”和“下一个灯”应忽略不计！*/
     N2S(null,null,false),N2E(null,null,false),W2E(null,null,false),W2N(null,null,false),
     /*由南向东和由西向北等右拐弯的灯不受红绿灯的控制，所以，可以假想它们总是绿灯*/
     S2E(null,null,true),E2N(null,null,true),N2W(null,null,true),W2S(null,null,true);

     private Lamp(String opposite,String next,boolean lighted){
         this.opposite = opposite;
         this.next = next;
         this.lighted = lighted;
     }

 
     /*当前灯是否为绿*/    
     private boolean lighted;
     /*与当前灯同时为绿的对应方向*/    
     private String opposite;
     /*当前灯变红时下一个变绿的灯*/    
     private String next;
     public boolean isLighted(){
         return lighted;
     }

     /**
      * 某个灯变绿时，它对应方向的灯也要变绿
      */    
     public void light(){
         this.lighted = true;
         if(opposite != null){
             Lamp.valueOf(opposite).light();
         }
         System.out.println(name() + " lamp is green，下面总共应该有6个方向能看到汽车穿过！");

     }

     /**
      * 某个灯变红时，对应方向的灯也要变红，并且下一个方向的灯要变绿
      * @return 下一个要变绿的灯
      */    
     public Lamp blackOut(){
         this.lighted = false;
         if(opposite != null){
             Lamp.valueOf(opposite).blackOut();
         }        

         Lamp nextLamp= null;
         if(next != null){
             nextLamp = Lamp.valueOf(next);
             System.out.println("绿灯从" + name() + "-------->切换为" + next);            
             nextLamp.light();
         }
         return nextLamp;
     }
 }

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