Detailed introduction to the use of enumerations in java

Author：Eve Cole Update Time：2024-11-18 19:12:02

Enum features

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

2. The constructor of an enumeration class can only use the private access modifier. If the access control modifier of its constructor is omitted, 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.

Copy the code code as follows:

public enum Week {
MON{
public String toLocaleString(){
return "Monday";
}
},TUES{
public String toLocaleString(){
return "Tuesday";
}
},WEB{
public String toLocaleString(){
return "Wednesday";
}

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

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

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

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

};
public abstract String toLocaleString();
}

Traversal of enumerations

Copy the code code as follows:

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

Common methods of enumeration

int compareTo method

String name() returns the name of the enumeration instance

int ordinal() returns the index of the enumeration value in the enumeration

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

public static valueOf()

Copy the code code as follows:

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());//Sunday
System.out.println(Week.values().length);//7 Get the enumeration length
}
}

Enum constructor

Copy the code code as follows:

public enum Gender {
MALE("male"),FEMALE("female");
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="Male";
break;
case FEMALE:
name="female";
break;
}
return name;
}

}

Comprehensive application example of enumeration: traffic light

Copy the code code as follows:

public enum Lamp {
/*Each enumeration element represents a control light in one direction*/
S2N("N2S","S2W",false),S2W("N2E","E2W",false),E2W("W2E","E2S",false),E2S("W2N","S2N",false ),
/*The elements below represent lights in the opposite direction to the elements above, and their "opposite direction lights" and "next lights" should be ignored! */
N2S(null,null,false),N2E(null,null,false),W2E(null,null,false),W2N(null,null,false),
/*Lights for right turns from south to east and from west to north are not controlled by traffic lights, so you can assume that they are always green lights*/
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;
}

/*Whether the current light is green*/
private boolean lighted;
/*The corresponding direction that the current light is green at the same time*/
private String opposite;
/*The next light to turn green when the current light turns red*/
private String next;
public boolean isLighted(){
return lighted;
}

/**
* When a certain light turns green, the light in its corresponding direction also turns green.
*/
public void light(){
this.lighted = true;
if(opposite != null){
Lamp.valueOf(opposite).light();
}
System.out.println(name() + "The lamp is green, there should be a total of 6 directions below where you can see cars passing through!");

}

/**
* When a certain light turns red, the light in the corresponding direction also turns red, and the light in the next direction turns green
* @return The next light to turn green
*/
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("The green light switches from " + name() + "--------> to " + next);
nextLamp.light();
}
return nextLamp;
}
}