what is enum

what is enum

  2월 19, 2022    Eunhan's library

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enum in Java

Definition

enum class is for define constant.
It will contain the value that will not change during the program is working

Reason for using the enum

debugging easily.

History

C: preprocessor : certain number
Java: static final String MALE: certain string
enum in Java: enum: certain object

C code example

#include <stdio.h>

#define MALE 1 // #define Preprocessor 

int main()
{
    const int FEMALE = 2; // const keyward
    
    int input = 2;
    
    if(input==MALE){
        printf("I am male");
    }else{
        printf("I am Female");
    }

    return 0;
}

result

I am Female

if you put 3 in input variable, it still print, "I am Female" We need additional if statement for checking the issue.

In Java, we started use "final." The final is not exactly same as the Preprocessor, But we used it with static final keyward

java code example

public class Main {

    public static final String MALE = "MALE";
    public static final String FEMALE = "FEMALE";

    public static void main(String[] args) {
        String gender;
        gender = Main.MALE;
        gender = "male"; //mistake, but no error
                
        if(gender.equals(Main.MALE)){
            System.out.println("I am male");
        }else{
            System.out.println("I am female");
        }        

    }
} 

result

I am female

However, still same issue stated. The constant's data type is String and it caused wrong result.

Thus, we use enum class since java 1.5.
We calls, "enumeration", "enumerated type", and "enum"

enum java code example

public class Main {

    public static void main(String[] args) {
        Gender gender;
        gender = Gender.MALE;
        gender = "male"; //mistake, but it shows error

        if(gender==Gender.MALE){
            System.out.println("I am male");
        }else{
            System.out.println("I am female");
        }

    }
}

enum Gender {MALE, FEMALE;}