get enum name from enum value

Question

I've read a lot about how obtain the corresponding name of an enum from its value using java, but no example seems to work for me! What is wrong?

public class Extensions {


    public enum RelationActiveEnum
    {
        Invited(0),
        Active(1),
        Suspended(2);

        private final int value;

        private RelationActiveEnum(final int value) {
            this.value = value;
        }
    }

}

and in another class I use:

        int dbValue = supp.ACTIVE;
        Extensions.RelationActiveEnum enumValue(dbValue);
        String stringName = enumValue.toString(); //Visible
        // OR
        int dbValuee = supp.ACTIVE;
        String stringValue = Enum.GetName(typeof(RelationActiveEnum), dbValue);

I should work, right? but it doesn't!!!! it tells me that dbValue cannote be cast to RelationActiveEnum...

Answer 1

Say we have:

public enum MyEnum {
  Test1, Test2, Test3
}

To get the name of a enum variable use name():

MyEnum e = MyEnum.Test1;
String name = e.name(); // Returns "Test1"

To get the enum from a (string) name, use valueOf():

String name = "Test1";
MyEnum e = Enum.valueOf(MyEnum.class, name);

If you require integer values to match enum fields, extend the enum class:

public enum MyEnum {
  Test1(1), Test2(2), Test3(3);

  public final int value;

  MyEnum(final int value) {
     this.value = value;
  }
}

Now you can use:

MyEnum e = MyEnum.Test1;
int value = e.value; // = 1

And lookup the enum using the integer value:

MyEnum getValue(int value) {
  for(MyEnum e: MyEnum.values()) {
    if(e.value == value) {
      return e;
    }
  }
  return null;// not found
}

Answer 2

Since your 'value' also happens to match with ordinals you could just do:

public enum RelationActiveEnum {
    Invited,
    Active,
    Suspended;

    private final int value;

    private RelationActiveEnum() {
        this.value = ordinal();
    }
}

And getting a enum from the value:

int value = 1;
RelationActiveEnum enumInstance = RelationActiveEnum.values()[value];

I guess an static method would be a good place to put this:

public enum RelationActiveEnum {
     public static RelationActiveEnum fromValue(int value) 
             throws IllegalArgumentException {
         try {
              return RelationActiveEnum.values()[value]
         } catch(ArrayIndexOutOfBoundsException e) {
              throw new IllegalArgumentException("Unknown enum value :"+ value);
         }
     }
}   

Obviously this all falls apart if your 'value' isn't the same value as the enum ordinal.

Answer 3

You could create a lookup method. Not the most efficient (depending on the enum's size) but it works.

public static String getNameByCode(int code){
  for(RelationActiveEnum e : RelationActiveEnum.values()){
    if(code == e.value) return e.name();
  }
  return null;
}

And call it like this:

RelationActiveEnum.getNameByCode(3);

Answer 4

What you can do is

RelationActiveEnum ae = Enum.valueOf(RelationActiveEnum.class,
                                     RelationActiveEnum.ACTIVE.name();

or

RelationActiveEnum ae = RelationActiveEnum.valueOf(
                                     RelationActiveEnum.ACTIVE.name();

or

// not recommended as the ordinal might not match the value
RelationActiveEnum ae = RelationActiveEnum.values()[
                                     RelationActiveEnum.ACTIVE.value];

By if you want to lookup by a field of an enum you need to construct a collection such as a List, an array or a Map.

public enum RelationActiveEnum {
    Invited(0),
    Active(1),
    Suspended(2);

    private final int code;

    private RelationActiveEnum(final int code) {
        this.code = code;
    }

    private static final Map<Integer, RelationActiveEnum> BY_CODE_MAP = new LinkedHashMap<>();
    static {
        for (RelationActiveEnum rae : RelationActiveEnum.values()) {
            BY_CODE_MAP.put(rae.code, rae);
        }
    }

    public static RelationActiveEnum forCode(int code) {
        return BY_CODE_MAP.get(code);
    }
}

allows you to write

String name = RelationActiveEnum.forCode(RelationActiveEnum.ACTIVE.code).name();

Answer 5

In my case value was not an integer but a String. getNameByCode method can be added to the enum to get name of a String value-

enum CODE {
    SUCCESS("SCS"), DELETE("DEL");

    private String status;

    /**
     * @return the status
     */
    public String getStatus() {
        return status;
    }

    /**
     * @param status
     *            the status to set
     */
    public void setStatus(String status) {
        this.status = status;
    }

    private CODE(String status) {
        this.status = status;
    }

    public static String getNameByCode(String code) {
        for (int i = 0; i < CODE.values().length; i++) {
            if (code.equals(CODE.values()[i].status))
                return CODE.values()[i].name();
        }
        return null;
    }

Answer 6

If you want something more efficient in runtime condition, you can have a map that contains every possible choice of the enum by their value. But it'll be juste slower at initialisation of the JVM.

import java.util.HashMap;
import java.util.Map;

/**
 * Example of enum with a getter that need a value in parameter, and that return the Choice/Instance 
 * of the enum which has the same value.
 * The value of each choice can be random.
 */
public enum MyEnum {
    /** a random choice */
    Choice1(4),
    /** a nother one */
    Choice2(2),
    /** another one again */
    Choice3(9);
    /** a map that contains every choices of the enum ordered by their value. */
    private static final Map<Integer, MyEnum> MY_MAP = new HashMap<Integer, MyEnum>();
    static {
        // populating the map
        for (MyEnum myEnum : values()) {
            MY_MAP.put(myEnum.getValue(), myEnum);
        }
    }
    /** the value of the choice */
    private int value;

    /**
     * constructor
     * @param value the value
     */
    private MyEnum(int value) {
        this.value = value;
    }

    /**
     * getter of the value
     * @return int
     */
    public int getValue() {
        return value;
    }

    /**
     * Return one of the choice of the enum by its value.
     * May return null if there is no choice for this value.
     * @param value value
     * @return MyEnum
     */
    public static MyEnum getByValue(int value) {
        return MY_MAP.get(value);
    }

    /**
     * {@inheritDoc}
     * @see java.lang.Enum#toString()
     */
    public String toString() {
        return name() + "=" + value;
    }

    /**
     * Exemple of how to use this class.
     * @param args args
     */
    public static void main(String[] args) {
        MyEnum enum1 = MyEnum.Choice1;
        System.out.println("enum1==>" + String.valueOf(enum1));
        MyEnum enum2GotByValue = MyEnum.getByValue(enum1.getValue());
        System.out.println("enum2GotByValue==>" + String.valueOf(enum2GotByValue));
        MyEnum enum3Unknown = MyEnum.getByValue(4);
        System.out.println("enum3Unknown==>" + String.valueOf(enum3Unknown));
    }
}

Answer 7

This is my take on it:

public enum LoginState { 
    LOGGED_IN(1), LOGGED_OUT(0), IN_TRANSACTION(-1);

    private int code;

    LoginState(int code) {
        this.code = code;
    }

    public int getCode() {
        return code;
    }

    public static LoginState getLoginStateFromCode(int code){
        for(LoginState e : LoginState.values()){
            if(code == e.code) return e;
        }
        return LoginState.LOGGED_OUT; //or null
    }
};

And I have used it with System Preferences in Android like so:

LoginState getLoginState(int i) {
    return LoginState.getLoginStateFromCode(
                prefs().getInt(SPK_IS_LOGIN, LoginState.LOGGED_OUT.getCode())
            );
}

public static void setLoginState(LoginState newLoginState) {
    editor().putInt(SPK_IS_LOGIN, newLoginState.getCode());
    editor().commit();
}

where pref and editor are SharedPreferences and a SharedPreferences.Editor