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Detailed explanation of usage of java enumeration type enum

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Release： 2020-06-17 15:18:16

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Detailed explanation of usage of java enumeration type enum

JDK1.5 introduces a new type - enumeration. Although it is a "small" function in Java, it brings "big" convenience to my development.

Senior brother, I will add my own understanding to help you understand.

Usage 1: Constants

Before JDK1.5, we defined constants as: public static final.... . Well, now with enumerations, related constants can be grouped into an enumeration type, and enumerations provide more methods than constants.

Java code

public enum Color {    RED, GREEN, BLANK, YELLOW  }

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Usage 2: switch

The switch statement before JDK1.6 only supports int, char, enum types, using enumerations , can make our code more readable.

Java code

enum Signal {      
    GREEN, YELLOW, RED  
}  
public class TrafficLight {      
    Signal color = Signal.RED;
          public void change() { 
             switch (color) { 
               case RED:  
               color = Signal.GREEN;    
                 break;   
                 case YELLOW:              
                 color = Signal.RED;              
                     break;          
                 case GREEN:              
                 color = Signal.YELLOW;              
                     break;          
       }      
     }  
}

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Usage three: Add new methods to the enumeration

If you plan to customize your own method, you must add it to the enum instance Add a semicolon at the end of the sequence. And Java requires that the enum instance must be defined first.

Java code

public enum Color {      
  RED("红色", 1), GREEN("绿色", 2), BLANK("白色", 3), YELLO("黄色", 4);      
  // 成员变量 
  private String name;      
  private int index;      
  // 构造方法     
  private Color(String name, int index) {        
  this.name = name;         
  this.index = index;     
 } 
 // 普通方法     
  public static String getName(int index) {        
     for (Color c : Color.values()) {              
           if (c.getIndex() == index) {                 
                 return c.name; 
      }          
   } 
    return null;     
 } 
 // get set 方法     
     public String getName() {       
        return name;
      } 
     public void setName(String name) {    
           this.name = name; 
     }      
     public int getIndex() {      
         return index; 
     }      
     public void setIndex(int index) { 
         this.index = index; 
     }  }  
}

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Usage 4: Overriding the enumeration method

The following is an example of overriding the toString() method.

Java code

public enum Color {    
  RED("红色", 1), GREEN("绿色", 2), BLANK("白色", 3), YELLO("黄色", 4);      
  // 成员变量      
  private String name;      
    private int index;      
    // 构造方法     
    private Color(String name, int index) { 
        this.name = name;
        this.index = index; 
     }      
//覆盖方法      @Override      
    public String toString() {       
   return this.index+"_"+this.name;
  }  
 }

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Usage five: Implement the interface

All enumerations inherit from the java.lang.Enum class. Since Java does not support multiple inheritance, enumeration objects cannot inherit from other classes.

Java code

public interface Behaviour {      
    void print();      
    String getInfo(); 
}  
public enum Color implements Behaviour{ 
    RED("红色", 1), GREEN("绿色", 2), BLANK("白色", 3), YELLO("黄色", 4);     
       // 成员变量   
    private String name;      
        private int index;      
        // 构造方法      
        private Color(String name, int index) { 
           this.name = name; 
       this.index = index;     
    } 
 //接口方法      
         @Override      
         public String getInfo() {
           return this.name; 
     }     
 //接口方法     
         @Override      
         public void print() {
          System.out.println(this.index+":"+this.name);
      }  
  }

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