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...
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();
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);
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
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));
}
}
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;
}
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: MyEunm.values()) {
if(e.value == value) {
return e;
}
}
return null;// not found
}
Source: Stackoverflow.com