Develop Reference

How to create an ENUM with a "new" value in Java?

How I can add new as a value to an enum in Java?
Here's my enum:
public enum AgentProspectStatus
{
loose("loose"),
on_progress("on_progress"),
reached("reached"),
alumni("alumni"),
student("student"),
new("new"); // This throws an error
private String code;
AgentProspectStatus(String code)
{
this.code = code;
}
}
The new("new") line is showing the error:
Unexpected Token

new is keyword in Java. In Java, enums should be spelled in uppercase and case_snake. Changing the case will fix your error.
public enum AgentProspectStatus {
LOOSE("loose"),
ON_PROGRESS("on_progress"),
REACHED("reached"),
ALUMNI("alumni"),
STUDENT("student"),
NEW("new");
private String code;
AgentProspectStatus(String code) {
this.code = code;
}
}

Looking up enum label by value

I have the following enum in my java android application:
static enum PaymentType
{
Scheme(0), Topup(1), Normal(2), Free(3), Promotion(4), Discount(5), Partial(6),
Refund(7), NoShow(8), Prepay(9), Customer(10), Return(11), Change(12), PettyCash(13),
StateTax(14), LocalTax(15), Voucher(16), Membership(17), Gratuity(18), Overpayment(19),
PrepayTime(20), HandlingFee(21);
private int value;
private PaymentType(int i) {
value = i;
}
public int getValue() {
return value;
}
}
I use this enum alot to find out the integer value of one of these string labels, for example int i = Lookups.PaymentType.Voucher.getValue();.
How can I do this the other way around? I have an integer value from a database and I need to find which string that corresponds to.

You should do something like this (static-init block should be at the end! and in your case just replace "asc" and "desc" with numbers, or add any other field):
public enum SortOrder {
ASC("asc"),
DESC("desc");
private static final HashMap<String, SortOrder> MAP = new HashMap<String, SortOrder>();
private String value;
private SortOrder(String value) {
this.value = value;
}
public String getValue() {
return this.value;
}
public static SortOrder getByName(String name) {
return MAP.get(name);
}
static {
for (SortOrder field : SortOrder.values()) {
MAP.put(field.getValue(), field);
}
}
}
After that, just call:
SortOrder asc = SortOrder.getByName("asc");

To go from an ordinal() index value back to enum:
type = PaymentType.values()[index];
However, keep in mind that this is fragile when the ordinal is stored anywhere else, such as a database. If the index numbers ever change, you'll get invalid results.
For more reliable lookup table, use a Map.

Design Issue | Enum to represent combo box options

I need to use an Enum with a combobox (values shown below).
YES (shown as YES on UI, stored in DB as Y)
NO (shown as NO on UI, stored in DB as N)
DEFAULT (shown as "" on UI, stored in DB as null)
The Enum has methods to perform the following -
toString() - to provide the custom String for UI. (showing the combo options)
OptionToDB (static) - Convert a selected option to db value (on save / update)
DBToOption (static)- Convert a DB value to selcted option (while loading the screen)
static enum EnumOption{
YES,NO,DEFAULT;
....
public static EnumOption DBToOption(String val){
if("Y".equals(val)){
return YES;
} else if("N".equals(val)){
return NO;
}else {
return DEFAULT;
}
}
....
}
It works pretty well, but the issue with above methods is that it uses if/else comparison to deduce which option / db value to be returned.
I thought of storing the dbValue as a field in enum but I was not able to reduce the if/else from DBToOption.
Can this if/else be avoided in any way using a better design??

If you store the dbValue as a field in the enum, you can remove the if/else and replace it with a for-loop, although I don't see anything wrong with those if/elses for this particular case:
static enum EnumOption {
YES("Y"),
NO("N"),
DEFAULT("");
private final String value;
private EnumOption(String value) {
this.value = value;
}
public static EnumOption DBToOption(String val) {
for (EnumOption opt : EnumOption.values()) {
if (opt.value.equals(val)) {
return opt;
}
}
return DEFAULT;
}
}

public enum EnumOption {
YES("Y"), NO("N"), DEFAULT("");
private final String value;
private final static Map<String, EnumOption> options;
static {
options = new HashMap<String, EnumOption>();
for (EnumOption opt : EnumOption.values()) {
options.put(opt.value, opt);
}
}
private EnumOption(String value) {
this.value = value;
}
public static EnumOption DBToOption(String val) {
return options.get(val) != null ? options.get(val) : DEFAULT;
}
}
And here is the test that proves it works.
public void testDBToOption() {
assertEquals(EnumOption.NO, EnumOption.DBToOption("N"));
assertEquals(EnumOption.YES, EnumOption.DBToOption("Y"));
assertEquals(EnumOption.DEFAULT, EnumOption.DBToOption(""));
assertEquals(EnumOption.DEFAULT, EnumOption.DBToOption(null));
assertEquals(EnumOption.DEFAULT, EnumOption.DBToOption("R"));
}

So you want to get rid of the remaining if/else ...Are you doing Object Calisthenics?
You could do the following, if you do not have compatibility issues:
public enum EnumOption {
Y("Y", "YES"),
N("N", "NO"),
D("D", "");
private final String dbValue;
private final String uiValue;
private EnumOption(String dbValue, String uiValue) {
this.dbValue = dbValue;
this.uiValue = uiValue;
}
public String getDbValue() {
return this.dbValue;
}
public String uiValue() {
return this.uiValue;
}
public static EnumOption getFromDb(String dbValue) {
return EnumOption.valueOf(dbValue);
}
}
Since each enum value can only occur once, this has at least the same performance as all the other implementations.
For details about the automatically generated valueOf(String) method in enum types, and James DW's solution, you can read up in Josh Bloch's Effective Java Item 30 (Use enums instead of int constants), page 154.

Get enum by its inner field

Have enum with inner fields, kind of map.
Now I need to get enum by its inner field.
Wrote this:
package test;
/**
* Test enum to test enum =)
*/
public enum TestEnum {
ONE(1), TWO(2), THREE(3);
private int number;
TestEnum(int number) {
this.number = number;
}
public TestEnum findByKey(int i) {
TestEnum[] testEnums = TestEnum.values();
for (TestEnum testEnum : testEnums) {
if (testEnum.number == i) {
return testEnum;
}
}
return null;
}
}
But it's not very efficient to look up through all enums each time I need to find appropriate instance.
Is there any other way to do the same?

You can use a static Map<Integer,TestEnum> with a static initializer that populates it with the TestEnum values keyed by their number fields.
Note that findByKey has been made static, and number has also been made final.
import java.util.*;
public enum TestEnum {
ONE(1), TWO(2), SIXTY_NINE(69);
private final int number;
TestEnum(int number) {
this.number = number;
}
private static final Map<Integer,TestEnum> map;
static {
map = new HashMap<Integer,TestEnum>();
for (TestEnum v : TestEnum.values()) {
map.put(v.number, v);
}
}
public static TestEnum findByKey(int i) {
return map.get(i);
}
public static void main(String[] args) {
System.out.println(TestEnum.findByKey(69)); // prints "SIXTY_NINE"
System.out.println(
TestEnum.values() == TestEnum.values()
); // prints "false"
}
}
You can now expect findByKey to be a O(1) operation.
References
JLS 8.7 Static initializers
JLS 8.9 Enums
Related questions
Static initalizer in Java
How to Initialise a static Map in Java
Note on values()
The second println statement in the main method is revealing: values() returns a newly allocated array with every invokation! The original O(N) solution could do a little better by only calling values() once and caching the array, but that solution would still be O(N) on average.

Although someone has suggested using Map<Integer, TestEnum> think twice about it.
Your original solution, especially for small enums, may be magnitudes faster than using HashMap.
HashMap will probably be not faster until your enum contains at least 30 to 40 elements.
This is one case of "If it ain't broken, don't fix it".

Here is the most convenient way to find enum value by its field:
public enum TestEnum {
A("EXAMPLE_1", "Qwerty", 1),
B("EXAMPLE_2", "Asdfgh", 2),
C("EXAMPLE_3", "Zxcvbn", 3);
private final String code;
private final String name;
private final Integer typeID;
TestEnum(String code, String name, Integer typeID) {
this.code = code;
this.name = name;
this.key = typeID;
}
public String getCode() {
return code;
}
public String getName() {
return name;
}
public Integer getKey() {
return key;
}
public static TestEnum findValueByTypeId(Integer key) {
return Arrays.stream(TestEnum.values()).filter(v ->
v.getKey().equals(key)).findFirst().orElseThrow(() ->
new Exception(String.format("Unknown TestEnum.key: '%s'", key)));
}
}

You should have a HashMap with the numbers as keys and the enum values as values.
This map can typically be in your repository. Then you can easily replace an int variable from the database with your preferred enum value.
If your keys (int values) are stored in a database, then I will say its bad design to carry those keys around in an enum on your business layer. If that's the case, I will recommend not to store the int value in the enum.

One solution is to add
public final Test[] TESTS = { null, ONE, TWO, THREE };
public static Test getByNumber(int i) {
return TESTS[i];
}
To the enum.
If the internal data is not an integer, you could have a Map which you populate in a static { ... } initializer. This map could later be used in the getByNumber method above.

How can I lookup a Java enum from its String value?

I would like to lookup an enum from its string value (or possibly any other value). I've tried the following code but it doesn't allow static in initialisers. Is there a simple way?
public enum Verbosity {
BRIEF, NORMAL, FULL;
private static Map<String, Verbosity> stringMap = new HashMap<String, Verbosity>();
private Verbosity() {
stringMap.put(this.toString(), this);
}
public static Verbosity getVerbosity(String key) {
return stringMap.get(key);
}
};

Use the valueOf method which is automatically created for each Enum.
Verbosity.valueOf("BRIEF") == Verbosity.BRIEF
For arbitrary values start with:
public static Verbosity findByAbbr(String abbr){
for(Verbosity v : values()){
if( v.abbr().equals(abbr)){
return v;
}
}
return null;
}
Only move on later to Map implementation if your profiler tells you to.
I know it's iterating over all the values, but with only 3 enum values it's hardly worth any other effort, in fact unless you have a lot of values I wouldn't bother with a Map it'll be fast enough.

You're close. For arbitrary values, try something like the following:
public enum Day {
MONDAY("M"), TUESDAY("T"), WEDNESDAY("W"),
THURSDAY("R"), FRIDAY("F"), SATURDAY("Sa"), SUNDAY("Su"), ;
private final String abbreviation;
// Reverse-lookup map for getting a day from an abbreviation
private static final Map<String, Day> lookup = new HashMap<String, Day>();
static {
for (Day d : Day.values()) {
lookup.put(d.getAbbreviation(), d);
}
}
private Day(String abbreviation) {
this.abbreviation = abbreviation;
}
public String getAbbreviation() {
return abbreviation;
}
public static Day get(String abbreviation) {
return lookup.get(abbreviation);
}
}

with Java 8 you can achieve with this way:
public static Verbosity findByAbbr(final String abbr){
return Arrays.stream(values()).filter(value -> value.abbr().equals(abbr)).findFirst().orElse(null);
}

#Lyle's answer is rather dangerous and I have seen it not work particularly if you make the enum a static inner class. Instead I have used something like this which will load the BootstrapSingleton maps before the enums.
Edit this should not be a problem any more with modern JVMs (JVM 1.6 or greater) but I do think there are still issues with JRebel but I haven't had a chance to retest it.
Load me first:
public final class BootstrapSingleton {
// Reverse-lookup map for getting a day from an abbreviation
public static final Map<String, Day> lookup = new HashMap<String, Day>();
}
Now load it in the enum constructor:
public enum Day {
MONDAY("M"), TUESDAY("T"), WEDNESDAY("W"),
THURSDAY("R"), FRIDAY("F"), SATURDAY("Sa"), SUNDAY("Su"), ;
private final String abbreviation;
private Day(String abbreviation) {
this.abbreviation = abbreviation;
BootstrapSingleton.lookup.put(abbreviation, this);
}
public String getAbbreviation() {
return abbreviation;
}
public static Day get(String abbreviation) {
return lookup.get(abbreviation);
}
}
If you have an inner enum you can just define the Map above the enum definition and that (in theory) should get loaded before.

And you can't use valueOf()?
Edit: Btw, there is nothing stopping you from using static { } in an enum.

In case it helps others, the option I prefer, which is not listed here, uses Guava's Maps functionality:
public enum Vebosity {
BRIEF("BRIEF"),
NORMAL("NORMAL"),
FULL("FULL");
private String value;
private Verbosity(final String value) {
this.value = value;
}
public String getValue() {
return this.value;
}
private static ImmutableMap<String, Verbosity> reverseLookup =
Maps.uniqueIndex(Arrays.asList(Verbosity.values()), Verbosity::getValue);
public static Verbosity fromString(final String id) {
return reverseLookup.getOrDefault(id, NORMAL);
}
}
With the default you can use null, you can throw IllegalArgumentException or your fromString could return an Optional, whatever behavior you prefer.

since java 8 you can initialize the map in a single line and without static block
private static Map<String, Verbosity> stringMap = Arrays.stream(values())
.collect(Collectors.toMap(Enum::toString, Function.identity()));

public enum EnumRole {
ROLE_ANONYMOUS_USER_ROLE ("anonymous user role"),
ROLE_INTERNAL ("internal role");
private String roleName;
public String getRoleName() {
return roleName;
}
EnumRole(String roleName) {
this.roleName = roleName;
}
public static final EnumRole getByValue(String value){
return Arrays.stream(EnumRole.values()).filter(enumRole -> enumRole.roleName.equals(value)).findFirst().orElse(ROLE_ANONYMOUS_USER_ROLE);
}
public static void main(String[] args) {
System.out.println(getByValue("internal role").roleName);
}
}

Perhaps, take a look at this. Its working for me.
The purpose of this is to lookup 'RED' with '/red_color'.
Declaring a static map and loading the enums into it only once would bring some performance benefits if the enums are many.
public class Mapper {
public enum Maps {
COLOR_RED("/red_color", "RED");
private final String code;
private final String description;
private static Map<String, String> mMap;
private Maps(String code, String description) {
this.code = code;
this.description = description;
}
public String getCode() {
return name();
}
public String getDescription() {
return description;
}
public String getName() {
return name();
}
public static String getColorName(String uri) {
if (mMap == null) {
initializeMapping();
}
if (mMap.containsKey(uri)) {
return mMap.get(uri);
}
return null;
}
private static void initializeMapping() {
mMap = new HashMap<String, String>();
for (Maps s : Maps.values()) {
mMap.put(s.code, s.description);
}
}
}
}
Please put in your opinons.

If you want a default value and don't want to build lookup maps, you can create a static method to handle that.
This example also handles lookups where the expected name would start with a number.
public static final Verbosity lookup(String name) {
return lookup(name, null);
}
public static final Verbosity lookup(String name, Verbosity dflt) {
if (StringUtils.isBlank(name)) {
return dflt;
}
if (name.matches("^\\d.*")) {
name = "_"+name;
}
try {
return Verbosity.valueOf(name);
} catch (IllegalArgumentException e) {
return dflt;
}
}
If you need it on a secondary value, you would just build the lookup map first like in some of the other answers.

You can define your Enum as following code :
public enum Verbosity
{
BRIEF, NORMAL, FULL, ACTION_NOT_VALID;
private int value;
public int getValue()
{
return this.value;
}
public static final Verbosity getVerbosityByValue(int value)
{
for(Verbosity verbosity : Verbosity.values())
{
if(verbosity.getValue() == value)
return verbosity ;
}
return ACTION_NOT_VALID;
}
#Override
public String toString()
{
return ((Integer)this.getValue()).toString();
}
};
See following link for more clarification

You can use the Enum::valueOf() function as suggested by Gareth Davis & Brad Mace above, but make sure you handle the IllegalArgumentException that would be thrown if the string used is not present in the enum.