Reverse Enum constants from strings and values in Java


--Sample code to get an Enum constant from a value in Java --Build the sample code with the javac command and run it with the java command --Operation check environment: macOS Catalina + Java 8 (AdoptOpenJDK 1.8.0_242-b08)

Enums are available from Java 5 (codename Tiger)


Tiger linguistically supports the types listed in the Java ™ programming language. The simplest form of enumeration is similar to the C, C ++, and C # formats.

Sample code

package com.example.enums;

/**Define a simple enum*/
public enum MetaName {
package com.example.enums;

/**Define an enum with one value*/
public enum OneValueEnum {

  ONE(1), TWO(2), THREE(3);

  private final int number;

   *Generate an enum constant by specifying a value.
  OneValueEnum(int number) {
    this.number = number;

   *Prepare a method that returns a value.
  public int getNumber() {
    return number;

   *Returns an enum constant that matches the value.
  public static OneValueEnum getByNumber(int number) {
    //Processing that identifies and returns an enum constant from a value
    for (OneValueEnum value : OneValueEnum.values()) {
      if (value.getNumber() == number) {
        return value;
    return null; //If not identifiable
package com.example;

import com.example.enums.MetaName;
import com.example.enums.OneValueEnum;

public class Main {

  public static void main(String[] args) {

  private static void testMetaName() {
    try {
      //You can get an Enum constant from a string using the auto-generated valueOf method
      System.out.println("***** FOO *****");
      MetaName foo = MetaName.valueOf("FOO");
      System.out.println("foo.getClass=" + foo.getClass());
      System.out.println("foo.getDeclaringClass=" + foo.getDeclaringClass());
      System.out.println("foo.toString=" + foo.toString());

      //IllegalArgumentException occurs when trying to get a constant that does not exist
      System.out.println("***** bar *****");
      MetaName bar = MetaName.valueOf("bar");
    } catch (Exception e) {

  private static void testOneValueEnum() {
    try {
      //You can get an Enum constant from a string using the auto-generated valueOf method
      System.out.println("***** ONE *****");
      OneValueEnum one = OneValueEnum.valueOf("ONE");
      System.out.println("one.getClass=" + one.getClass());
      System.out.println("one.getDeclaringClass=" + one.getDeclaringClass());
      System.out.println("one.toString=" + one.toString());
      System.out.println("one.getNumber=" + one.getNumber());

      //In order to get the Enum constant that matches the value, you need to implement it yourself.
      System.out.println("***** 1 *****");
      OneValueEnum ichi = OneValueEnum.getByNumber(1); //Call your own implementation method
      System.out.println("ichi.getClass=" + ichi.getClass());
      System.out.println("ichi.getDeclaringClass=" + ichi.getDeclaringClass());
      System.out.println("ichi.toString=" + ichi.toString());
      System.out.println("ichi.getNumber=" + ichi.getNumber());

      //Since there was no Enum constant that matches the value, null is returned.
      // (Since it is self-implemented, you can do any processing)
      System.out.println("***** 9 *****");
      OneValueEnum kyu = OneValueEnum.getByNumber(9);
      System.out.println("kyu=" + kyu);
    } catch (Exception e) {

Build sample code

Place the source code.

$ tree
└── src
    └── com
        └── example
            └── enums

Create a directory to output the class file.

$ mkdir dest

Compile with the javac command.

$ javac -sourcepath src src/com/example/ -d dest

Confirm that the class file has been generated.

$ tree
├── dest
│   └── com
│       └── example
│           ├── Main.class
│           └── enums
│               ├── MetaName.class
│               └── OneValueEnum.class
└── src
    └── com
        └── example
            └── enums

Sample execution result

$ java -classpath dest com.example.Main
***** FOO *****
foo.getClass=class com.example.enums.MetaName
foo.getDeclaringClass=class com.example.enums.MetaName
***** bar *****
java.lang.IllegalArgumentException: No enum constant
	at java.lang.Enum.valueOf(
	at com.example.enums.MetaName.valueOf(
	at com.example.Main.testMetaName(
	at com.example.Main.main(
***** ONE *****
one.getClass=class com.example.enums.OneValueEnum
one.getDeclaringClass=class com.example.enums.OneValueEnum
***** 1 *****
ichi.getClass=class com.example.enums.OneValueEnum
ichi.getDeclaringClass=class com.example.enums.OneValueEnum
***** 9 *****

Reference material

-JDK 5.0 documentation -enum

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