Related
I have some UI client filters (combobox and checkbox group) that I need to use on server side: I thought to use an enum to identify filter types and others enums to identify each filter's options.
// All UI filters
public enum FilterType {
AGGREGATION("aggregation"),
AREA("area"),
PRODUCTION("production"),
DATA_TYPE("datatype"),
PRODUCER("producer"),
NETWORK("network"),
SOURCE("source");
private String value;
private FilterType(String value) {
this.value = value;
}
public String getValue() {
return value;
}
}
// FilterType.AGGREGATION filter options
public enum AggregationOptionType {
STANDARD("standard"),
DTR("dtr"),
CO("co");
private String value;
private AggregationOptionType(String value) {
this.value = value;
}
public String getValue() {
return value;
}
}
I would like to craete a hard link between FilterType.AGGREGATION and AggregationOptionType forcing the access to an option via FilterType.AGGREGATION.DTR.
How can I "nest" an enum inside a value of another enum?
Are there other patterns (maybe smarter than mine) to achieve the same result?
EDIT
A clarification: I do NOT need to assign to each value of the outer enum a value of a common inner enum. I need to assign a whole different inner enum to each value of the outer enum.
You can put one enum into another, like:
enum OuterEnum {
A, B;
enum InnerEnum {
C, D;
}
}
To use like:
class Enumuser {
OuterEnum.InnerEnum ie = OuterEnum.InnerEnum.C;
}
But of course, that is not exactly what you are looking for.
You need to go one step further:
enum OuterEnum {
A(InnerEnum.C), B(InnerEnum.D);
private final InnerEnum inner;
private OuterEnum(InnerEnum inner) { this.inner = inner; }
public InnerEnum getInner() { return inner; }
enum InnerEnum {
C, D;
}
}
class Enumuser {
OuterEnum.InnerEnum inner = OuterEnum.A.getInner();
}
But a final word of warning: don't get too hang up on using enums for such purposes. You see, as soon as you start writing switch statements all over the place that switch over such enums, in order to do this or that ... you are probably doing something wrong. Consider not "falling into that enum trap" please.
Instead you should be looking into using polymorphism, like shown here!
You can add it to the Enum, as a variable.
But only if you can have all the sub Enums under the same enum type ie
public enum FilterType {
AGGREGATION("aggregation",Subfilter.DTR);
}
You can do something like as follows:
//All UI filters
public interface FilterType {
// FilterType.AGGREGATION
public interface AGGREGATION {
// FilterType.AGGREGATION filter options
enum AggregationOptionType {
STANDARD("standard"),
DTR("dtr"),
CO("co");
private String value;
private AggregationOptionType(String value) {
this.value = value;
}
public String getValue() {
return value;
}
}
}
}
e.g. for AGGREGATION
Just use it in the same way like a String value and if you want to have a single file, so hold your enums in a interface class:
public interface Enums {
public enum FilterType {
AGGREGATION("aggregation", AggregationOptionType.DTR),
AREA("area"),
PRODUCTION("production"),
DATA_TYPE("datatype"),
PRODUCER("producer"),
NETWORK("network", AggregationOptionType.CO),
SOURCE("source");
public final String value;
public final AggregationOptionType type;
private FilterType(String value, AggregationOptionType typy) {
this.value = value;
this.type = typy;
}
private FilterType(String value) {
this.value = value;
this.type = AggregationOptionType.STANDARD;
}
}
public enum AggregationOptionType {
STANDARD("standard"),
DTR("dtr"),
CO("co");
public final String value;
private AggregationOptionType(String value) {
this.value = value;
}
}
}
Good day SO people. I have a problem regarding returning the inner enum values of my enum. I do not know which return type to use. I have tried googling and bumped into some solutions the uses generics however, I still have no luck. I do not know if my question has a solution or probably I did a bad design. So here goes, below
is my enum.
public enum KEYS
{
A("value"),
B("value"),
C("value");
public enum KEYS_GROUP_A
{
ITEM_A ("value"),
ITEM_B ("value"),
ITEM_C ("value");
private String value;
private KEYS_GROUP_A( String _value )
{
value = _value;
}
public String getVal()
{
return value;
}
}
public enum KEYS_GROUP_B
{
ITEM_A ("value"),
ITEM_B ("value"),
ITEM_C ("value");
private String value;
private KEYS_GROUP_B( String _value )
{
value = _value;
}
public String getVal()
{
return value;
}
}
public enum KEYS_GROUP_C
{
ITEM_A ("value"),
ITEM_B ("value"),
ITEM_C ("value");
private String value;
private KEYS_GROUP_C( String _value )
{
value = _value;
}
public String getVal()
{
return value;
}
}
private String value;
private PROPERTY_KEYS(String _value)
{
value = _value;
}
public String getVal()
{
return value;
}
public <?> getEnumValues(int x)
{
if ( 0 == x )
{
return KEYS.KEYS_GROUP_A.values();
}
else if ( 1 == x )
{
return KEYS.KEYS_GROUP_B.values();
}
else
{
return KEYS.KEYS_GROUP_C.values();
}
}
}
What I am trying to do is the getEnumValues() method. I have tried the return type <T extends Enum<T>> T but still an error occurs. Please tell if my design is bad or should not really be done. Please state some references. I'm willing to read and learn. Please shed some light! Thanks in advance!
The most specific type you can return is
public Enum<?>[] getEnumValues(int x)
You can return a more "useful" type if you define an interface like this:
interface HasVal { String getVal(); }
then make your enums all implement that interface, e.g.:
public enum KEYS_GROUP_A implements HasVal {
// ...
#Override public String getVal() { return value; }
}
Then you can return
public HasVal[] getEnumValues(int x)
and be able to invoke the getVal method on the instances:
for (HasVal val : getEnumValues(x)) {
System.out.println(val.getVal());
}
You can't use:
public <T extends Enum<T>> T[] getEnumValues(int x)
because this isn't satisfiable for a general T. For instance, I could define:
enum Blah {}
and then try to invoke:
Blah[] blah = getEnumValues(1);
That wouldn't be type safe, because at least one (well, all, actually) of the code paths return a value which is not covariant with Blah[].
What is the best way to use the values stored in an Enum as String literals?
For example:
public enum Modes {
some-really-long-string,
mode1,
mode2,
mode3
}
Then later I could use Mode.mode1 to return its string representation as mode1. Without having to keep calling Mode.mode1.toString().
You can't. I think you have FOUR options here. All four offer a solution but with a slightly different approach...
Option One: use the built-in name() on an enum. This is perfectly fine if you don't need any special naming format.
String name = Modes.mode1.name(); // Returns the name of this enum constant, exactly as declared in its enum declaration.
Option Two: add overriding properties to your enums if you want more control
public enum Modes {
mode1 ("Fancy Mode 1"),
mode2 ("Fancy Mode 2"),
mode3 ("Fancy Mode 3");
private final String name;
private Modes(String s) {
name = s;
}
public boolean equalsName(String otherName) {
// (otherName == null) check is not needed because name.equals(null) returns false
return name.equals(otherName);
}
public String toString() {
return this.name;
}
}
Option Three: use static finals instead of enums:
public final class Modes {
public static final String MODE_1 = "Fancy Mode 1";
public static final String MODE_2 = "Fancy Mode 2";
public static final String MODE_3 = "Fancy Mode 3";
private Modes() { }
}
Option Four: interfaces have every field public, static and final:
public interface Modes {
String MODE_1 = "Fancy Mode 1";
String MODE_2 = "Fancy Mode 2";
String MODE_3 = "Fancy Mode 3";
}
Every enum has both a name() and a valueOf(String) method. The former returns the string name of the enum, and the latter gives the enum value whose name is the string. Is this like what you're looking for?
String name = Modes.mode1.name();
Modes mode = Modes.valueOf(name);
There's also a static valueOf(Class, String) on Enum itself, so you could also use:
Modes mode = Enum.valueOf(Modes.class, name);
You could override the toString() method for each enum value.
Example:
public enum Country {
DE {
#Override
public String toString() {
return "Germany";
}
},
IT {
#Override
public String toString() {
return "Italy";
}
},
US {
#Override
public String toString() {
return "United States";
}
}
}
Usage:
public static void main(String[] args) {
System.out.println(Country.DE); // Germany
System.out.println(Country.IT); // Italy
System.out.println(Country.US); // United States
}
As Benny Neugebauer mentions, you could overwrite the toString(). However instead overwriting the toString for each enum field I like more something like this:
public enum Country{
SPAIN("España"),
ITALY("Italia"),
PORTUGAL("Portugal");
private String value;
Country(final String value) {
this.value = value;
}
public String getValue() {
return value;
}
#Override
public String toString() {
return this.getValue();
}
}
You could also add a static method to retrieve all the fields, to print them all, etc.
Simply call getValue to obtain the string associated to each Enum item
mode1.name() or String.valueOf(mode1). It doesn't get better than that, I'm afraid
public enum Modes {
MODE1("Mode1"),
MODE2("Mode2"),
MODE3("Mode3");
private String value;
public String getValue() {
return value;
}
private Modes(String value) {
this.value = value;
}
}
you can make a call like below wherever you want to get the value as a string from the enum.
Modes.MODE1.getvalue();
This will return "Mode1" as a String.
For my enums I don't really like to think of them being allocated with 1 String each. This is how I implement a toString() method on enums.
enum Animal
{
DOG, CAT, BIRD;
public String toString(){
switch (this) {
case DOG: return "Dog";
case CAT: return "Cat";
case BIRD: return "Bird";
}
return null;
}
}
You can use Mode.mode1.name() however you often don't need to do this.
Mode mode =
System.out.println("The mode is "+mode);
As far as I know, the only way to get the name would be
Mode.mode1.name();
If you really need it this way, however, you could do:
public enum Modes {
mode1 ("Mode1"),
mode2 ("Mode2"),
mode3 ("Mode3");
private String name;
private Modes(String s) {
name = s;
}
}
my solution for your problem!
import java.util.HashMap;
import java.util.Map;
public enum MapEnumSample {
Mustang("One of the fastest cars in the world!"),
Mercedes("One of the most beautiful cars in the world!"),
Ferrari("Ferrari or Mercedes, which one is the best?");
private final String description;
private static Map<String, String> enumMap;
private MapEnumSample(String description) {
this.description = description;
}
public String getEnumValue() {
return description;
}
public static String getEnumKey(String name) {
if (enumMap == null) {
initializeMap();
}
return enumMap.get(name);
}
private static Map<String, String> initializeMap() {
enumMap = new HashMap<String, String>();
for (MapEnumSample access : MapEnumSample.values()) {
enumMap.put(access.getEnumValue(), access.toString());
}
return enumMap;
}
public static void main(String[] args) {
// getting value from Description
System.out.println(MapEnumSample.getEnumKey("One of the fastest cars in the world!"));
// getting value from Constant
System.out.println(MapEnumSample.Mustang.getEnumValue());
System.out.println(MapEnumSample.getEnumKey("One of the most beautiful cars in the world!"));
System.out.println(MapEnumSample.Mercedes.getEnumValue());
// doesnt exist in Enum
System.out.println("Mustang or Mercedes, which one is the best?");
System.out.println(MapEnumSample.getEnumKey("Mustang or Mercedes, which one is the best?") == null ? "I don't know!" : "I believe that "
+ MapEnumSample.getEnumKey("Ferrari or Mustang, which one is the best?") + " is the best!.");
// exists in Enum
System.out.println("Ferrari or Mercedes, wich one is the best?");
System.out.println(MapEnumSample.getEnumKey("Ferrari or Mercedes, which one is the best?") == null ? "I don't know!" : "I believe that "
+ MapEnumSample.getEnumKey("Ferrari or Mercedes, which one is the best?") + " is the best!");
}
}
You can simply use:
""+ Modes.mode1
public enum Environment
{
PROD("https://prod.domain.com:1088/"),
SIT("https://sit.domain.com:2019/"),
CIT("https://cit.domain.com:8080/"),
DEV("https://dev.domain.com:21323/");
private String url;
Environment(String envUrl) {
this.url = envUrl;
}
public String getUrl() {
return url;
}
}
String prodUrl = Environment.PROD.getUrl();
It will print:
https://prod.domain.com:1088/
This design for enum string constants works in most of the cases.
Enum is just a little bit special class. Enums can store additional fields, implement methods etc. For example
public enum Modes {
mode1('a'),
mode2('b'),
mode3('c'),
;
char c;
private Modes(char c) {
this.c = c;
}
public char character() {
return c;
}
}
Now you can say:
System.out.println(Modes.mode1.character())
and see output:
a
package com.common.test;
public enum Days {
monday(1,"Monday"),tuesday(2,"Tuesday"),wednesday(3,"Wednesday"),
thrusday(4,"Thrusday"),friday(5,"Friday"),saturday(6,"Saturday"),sunday(7,"Sunday");
private int id;
private String desc;
Days(int id,String desc){
this.id=id;
this.desc=desc;
}
public static String getDay(int id){
for (Days day : Days.values()) {
if (day.getId() == id) {
return day.getDesc();
}
}
return null;
}
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getDesc() {
return desc;
}
public void setDesc(String desc) {
this.desc = desc;
}
};
This method should work with any enum:
public enum MyEnum {
VALUE1,
VALUE2,
VALUE3;
public int getValue() {
return this.ordinal();
}
public static DataType forValue(int value) {
return values()[value];
}
public String toString() {
return forValue(getValue()).name();
}
}
i found this one is more easy for preventing type error:
public enum Modes {
some-really-long-string,
mode1,
mode2,
mode3;
String str;
Modes(){
this.str = super.name();
}
#Override
#NonNull
public String toString() {
return str;
}
however - this may work when you need to use a String on a log/println or whenever java compiles the toString() method automatically, but on a code line like this ->
// sample method that require (string,value)
intent.putExtra(Modes.mode1 ,shareElement.getMode()); // java error
// first argument enum does not return value
instead as mentioned above you will still have to extend the enum and use .name() in those cases like this:
intent.putExtra(Modes.mode1.name() ,shareElement.getMode());
after many tries I have come with this solution
public static enum Operation {
Addition, Subtraction, Multiplication, Division,;
public String getUserFriendlyString() {
if (this==Addition) {
return " + ";
} else if (this==Subtraction) {
return " - ";
} else if (this==Multiplication) {
return " * ";
} else if (this==Division) {
return " / ";
}
return "undefined";
}
}
You can try this:
public enum Modes {
some-really-long-string,
mode1,
mode2,
mode3;
public String toString(){
switch(this) {
case some-really-long-string:
return "some-really-long-string";
case mode2:
return "mode2";
default: return "undefined";
}
}
}
use mode1.name() or String.valueOf(Modes.mode1)
Is it possible to create a generic method or class to retrieve an enum value from a given unique property (field with getter method)?
So you would have:
public enum EnumToMap {
E1("key1"),
E2("key2"),
;
private final String key;
private EnumToMap(String key) {
this.key = key;
}
public String getKey() {
return key;
}
}
so required is the same functionality as
public static EnumToMap getByKey(String key)
...
would provide. Preferably without reflection and as generic as possible (but in this case it may not be possible to create a generic solution without reflection).
Clarification: So this method should work for multiple enumerations. The idea is not to have to implement the lookup over and over again.
Actually possible just with generics and interface.
Create and implement interface
interface WithKeyEnum {
String getKey();
}
enum EnumToMap implements WithKeyEnum {
...
#Override
public String getKey() {
return key;
}
}
Implementation
public static <T extends Enum<T> & WithKeyEnum> T getByKey(Class<T> enumTypeClass, String key) {
for (T type : enumTypeClass.getEnumConstants()) {
if (type.getKey().equals(key)) {
return type;
}
}
throw new IllegalArgumentException();
}
Usage
EnumToMap instanceOfE1 = getByKey(EnumToMap.class, "key1");
If you want to drop generification and get O(1) complexity use HashMap to get it
public enum EnumToMap{
E1("key1"),
E2("key2");
private final String key;
private static final Map<String, EnumToMap> keys = new HashMap<String, EnumToMap>();
static {
for (EnumToMap value : values()) {
keys.put(value.getKey(), value);
}
}
private EnumToMap(String key) {
this.key = key;
}
public String getKey() {
return key;
}
public static EnumToMap getByKey(String key) {
return keys.get(key);
}
}
This would be hard to just generify as there must be an object to store the map. Enum itself seems to be good candidate for that.
When working with variables/parameters that can only take a finite number of values, I try to always use Java's enum, as in
public enum BonusType {
MONTHLY, YEARLY, ONE_OFF
}
As long as I stay inside my code, that works fine. However, I often need to interface with other code that uses plain int (or String) values for the same purpose, or I need to read/write from/to a database where the data is stored as a number or string.
In that case, I'd like to have a convenient way to associate each enum value with a an integer, such that I can convert both ways (in other words, I need a "reversible enum").
Going from enum to int is easy:
public enum BonusType {
public final int id;
BonusType(int id) {
this.id = id;
}
MONTHLY(1), YEARLY(2), ONE_OFF(3);
}
Then I can access the int value as BonusType x = MONTHLY; int id = x.id;.
However, I can see no nice way for the reverse, i.e. going from int to enum. Ideally, something like
BonusType bt = BonusType.getById(2);
The only solutions I could come up with are:
Put a lookup method into the enum, which uses BonusType.values() to fill a map "int -> enum", then caches that and uses it for lookups. Would work, but I'd have to copy this method identically into each enum I use :-(.
Put the lookup method into a static utility class. Then I'd only need one "lookup" method, but I'd have to fiddle with reflection to get it to work for an arbitrary enum.
Both methods seem terribly awkward for such a simple (?) problem.
Any other ideas/insights?
enum → int
yourEnum.ordinal()
int → enum
EnumType.values()[someInt]
String → enum
EnumType.valueOf(yourString)
enum → String
yourEnum.name()
A side-note:As you correctly point out, the ordinal() may be "unstable" from version to version. This is the exact reason why I always store constants as strings in my databases. (Actually, when using MySql, I store them as MySql enums!)
http://www.javaspecialists.co.za/archive/Issue113.html
The solution starts out similar to yours with an int value as part of the enum definition. He then goes on to create a generics-based lookup utility:
public class ReverseEnumMap<V extends Enum<V> & EnumConverter> {
private Map<Byte, V> map = new HashMap<Byte, V>();
public ReverseEnumMap(Class<V> valueType) {
for (V v : valueType.getEnumConstants()) {
map.put(v.convert(), v);
}
}
public V get(byte num) {
return map.get(num);
}
}
This solution is nice and doesn't require 'fiddling with reflection' because it's based on the fact that all enum types implicitly inherit the Enum interface.
I found this on the web, it was very helpful and simple to implement.
This solution was NOT made by me
http://www.ajaxonomy.com/2007/java/making-the-most-of-java-50-enum-tricks
public enum Status {
WAITING(0),
READY(1),
SKIPPED(-1),
COMPLETED(5);
private static final Map<Integer,Status> lookup
= new HashMap<Integer,Status>();
static {
for(Status s : EnumSet.allOf(Status.class))
lookup.put(s.getCode(), s);
}
private int code;
private Status(int code) {
this.code = code;
}
public int getCode() { return code; }
public static Status get(int code) {
return lookup.get(code);
}
}
Seems the answer(s) to this question are outdated with the release of Java 8.
Don't use ordinal as ordinal is unstable if persisted outside the
JVM such as a database.
It is relatively easy to create a static map
with the key values.
public enum AccessLevel {
PRIVATE("private", 0),
PUBLIC("public", 1),
DEFAULT("default", 2);
AccessLevel(final String name, final int value) {
this.name = name;
this.value = value;
}
private final String name;
private final int value;
public String getName() {
return name;
}
public int getValue() {
return value;
}
static final Map<String, AccessLevel> names = Arrays.stream(AccessLevel.values())
.collect(Collectors.toMap(AccessLevel::getName, Function.identity()));
static final Map<Integer, AccessLevel> values = Arrays.stream(AccessLevel.values())
.collect(Collectors.toMap(AccessLevel::getValue, Function.identity()));
public static AccessLevel fromName(final String name) {
return names.get(name);
}
public static AccessLevel fromValue(final int value) {
return values.get(value);
}
}
org.apache.commons.lang.enums.ValuedEnum;
To save me writing loads of boilerplate code or duplicating code for each Enum, I used Apache Commons Lang's ValuedEnum instead.
Definition:
public class NRPEPacketType extends ValuedEnum {
public static final NRPEPacketType TYPE_QUERY = new NRPEPacketType( "TYPE_QUERY", 1);
public static final NRPEPacketType TYPE_RESPONSE = new NRPEPacketType( "TYPE_RESPONSE", 2);
protected NRPEPacketType(String name, int value) {
super(name, value);
}
}
Usage:
int -> ValuedEnum:
NRPEPacketType packetType =
(NRPEPacketType) EnumUtils.getEnum(NRPEPacketType.class, 1);
You could perhaps use something like
interface EnumWithId {
public int getId();
}
enum Foo implements EnumWithId {
...
}
That would reduce the need for reflection in your utility class.
In this code, for permanent and intense search , have memory or process for use, and I select memory, with converter array as index.
I hope it's helpful
public enum Test{
VALUE_ONE(101, "Im value one"),
VALUE_TWO(215, "Im value two");
private final int number;
private final byte[] desc;
private final static int[] converter = new int[216];
static{
Test[] st = values();
for(int i=0;i<st.length;i++){
cv[st[i].number]=i;
}
}
Test(int value, byte[] description) {
this.number = value;
this.desc = description;
}
public int value() {
return this.number;
}
public byte[] description(){
return this.desc;
}
public static String description(int value) {
return values()[converter[rps]].desc;
}
public static Test fromValue(int value){
return values()[converter[rps]];
}
}
Use an interface to show it who's boss.
public interface SleskeEnum {
int id();
SleskeEnum[] getValues();
}
public enum BonusType implements SleskeEnum {
MONTHLY(1), YEARLY(2), ONE_OFF(3);
public final int id;
BonusType(int id) {
this.id = id;
}
public SleskeEnum[] getValues() {
return values();
}
public int id() { return id; }
}
public class Utils {
public static SleskeEnum getById(SleskeEnum type, int id) {
for(SleskeEnum t : type.getValues())
if(t.id() == id) return t;
throw new IllegalArgumentException("BonusType does not accept id " + id);
}
public static void main(String[] args) {
BonusType shouldBeMonthly = (BonusType)getById(BonusType.MONTHLY,1);
System.out.println(shouldBeMonthly == BonusType.MONTHLY);
BonusType shouldBeMonthly2 = (BonusType)getById(BonusType.MONTHLY,1);
System.out.println(shouldBeMonthly2 == BonusType.YEARLY);
BonusType shouldBeYearly = (BonusType)getById(BonusType.MONTHLY,2);
System.out.println(shouldBeYearly == BonusType.YEARLY);
BonusType shouldBeOneOff = (BonusType)getById(BonusType.MONTHLY,3);
System.out.println(shouldBeOneOff == BonusType.ONE_OFF);
BonusType shouldException = (BonusType)getById(BonusType.MONTHLY,4);
}
}
And the result:
C:\Documents and Settings\user\My Documents>java Utils
true
false
true
true
Exception in thread "main" java.lang.IllegalArgumentException: BonusType does not accept id 4
at Utils.getById(Utils.java:6)
at Utils.main(Utils.java:23)
C:\Documents and Settings\user\My Documents>
Both the .ordinal() and values()[i] are unstable since they are dependent to the order of enums. Thus if you change the order of enums or add/delete some your program would break.
Here is a simple yet effective method to map between enum and int.
public enum Action {
ROTATE_RIGHT(0), ROTATE_LEFT(1), RIGHT(2), LEFT(3), UP(4), DOWN(5);
public final int id;
Action(int id) {
this.id = id;
}
public static Action get(int id){
for (Action a: Action.values()) {
if (a.id == id)
return a;
}
throw new IllegalArgumentException("Invalid id");
}
}
Applying it for strings shouldn't be difficult.
A very clean usage example of reverse Enum
Step 1
Define an interface EnumConverter
public interface EnumConverter <E extends Enum<E> & EnumConverter<E>> {
public String convert();
E convert(String pKey);
}
Step 2
Create a class name ReverseEnumMap
import java.util.HashMap;
import java.util.Map;
public class ReverseEnumMap<V extends Enum<V> & EnumConverter<V>> {
private Map<String, V> map = new HashMap<String, V>();
public ReverseEnumMap(Class<V> valueType) {
for (V v : valueType.getEnumConstants()) {
map.put(v.convert(), v);
}
}
public V get(String pKey) {
return map.get(pKey);
}
}
Step 3
Go to you Enum class and implement it with EnumConverter<ContentType> and of course override interface methods. You also need to initialize a static ReverseEnumMap.
public enum ContentType implements EnumConverter<ContentType> {
VIDEO("Video"), GAME("Game"), TEST("Test"), IMAGE("Image");
private static ReverseEnumMap<ContentType> map = new ReverseEnumMap<ContentType>(ContentType.class);
private final String mName;
ContentType(String pName) {
this.mName = pName;
}
String value() {
return this.mName;
}
#Override
public String convert() {
return this.mName;
}
#Override
public ContentType convert(String pKey) {
return map.get(pKey);
}
}
Step 4
Now create a Communication class file and call it's new method to convert an Enum to String and String to Enum. I have just put main method for explanation purpose.
public class Communication<E extends Enum<E> & EnumConverter<E>> {
private final E enumSample;
public Communication(E enumSample) {
this.enumSample = enumSample;
}
public String resolveEnumToStringValue(E e) {
return e.convert();
}
public E resolveStringEnumConstant(String pName) {
return enumSample.convert(pName);
}
//Should not put main method here... just for explanation purpose.
public static void main(String... are) {
Communication<ContentType> comm = new Communication<ContentType>(ContentType.GAME);
comm.resolveEnumToStringValue(ContentType.GAME); //return Game
comm.resolveStringEnumConstant("Game"); //return GAME (Enum)
}
}
Click for for complete explanation
I'm not sure if it's the same in Java, but enum types in C are automatically mapped to integers as well so you can use either the type or integer to access it. Have you tried simply accessing it with integer yet?
Really great question :-) I used solution similar to Mr.Ferguson`s sometime ago. Our decompiled enum looks like this:
final class BonusType extends Enum
{
private BonusType(String s, int i, int id)
{
super(s, i);
this.id = id;
}
public static BonusType[] values()
{
BonusType abonustype[];
int i;
BonusType abonustype1[];
System.arraycopy(abonustype = ENUM$VALUES, 0, abonustype1 = new BonusType[i = abonustype.length], 0, i);
return abonustype1;
}
public static BonusType valueOf(String s)
{
return (BonusType)Enum.valueOf(BonusType, s);
}
public static final BonusType MONTHLY;
public static final BonusType YEARLY;
public static final BonusType ONE_OFF;
public final int id;
private static final BonusType ENUM$VALUES[];
static
{
MONTHLY = new BonusType("MONTHLY", 0, 1);
YEARLY = new BonusType("YEARLY", 1, 2);
ONE_OFF = new BonusType("ONE_OFF", 2, 3);
ENUM$VALUES = (new BonusType[] {
MONTHLY, YEARLY, ONE_OFF
});
}
}
Seeing this is apparent why ordinal() is unstable. It is the i in super(s, i);. I'm also pessimistic that you can think of a more elegant solution than these you already enumerated. After all enums are classes as any final classes.
For the sake of completeness, here is a generic approach to retrieve enum values by index from any enum type. My intention was to make the method look and feel like Enum.valueOf(Class, String). Fyi, i copied this method from here.
Index related issues (already discussed in depth here) still apply.
/**
* Returns the {#link Enum} instance for a given ordinal.
* This method is the index based alternative
* to {#link Enum#valueOf(Class, String)}, which
* requires the name of an instance.
*
* #param <E> the enum type
* #param type the enum class object
* #param ordinal the index of the enum instance
* #throws IndexOutOfBoundsException if ordinal < 0 || ordinal >= enums.length
* #return the enum instance with the given ordinal
*/
public static <E extends Enum<E>> E valueOf(Class<E> type, int ordinal) {
Preconditions.checkNotNull(type, "Type");
final E[] enums = type.getEnumConstants();
Preconditions.checkElementIndex(ordinal, enums.length, "ordinal");
return enums[ordinal];
}
Int -->String :
public enum Country {
US("US",0),
UK("UK",2),
DE("DE",1);
private static Map<Integer, String> domainToCountryMapping;
private String country;
private int domain;
private Country(String country,int domain){
this.country=country.toUpperCase();
this.domain=domain;
}
public String getCountry(){
return country;
}
public static String getCountry(String domain) {
if (domainToCountryMapping == null) {
initMapping();
}
if(domainToCountryMapping.get(domain)!=null){
return domainToCountryMapping.get(domain);
}else{
return "US";
}
}
private static void initMapping() {
domainToCountryMapping = new HashMap<Integer, String>();
for (Country s : values()) {
domainToCountryMapping.put(s.domain, s.country);
}
}
I needed something different because I wanted to use a generic approach. I'm reading the enum to and from byte arrays. This is where I come up with:
public interface EnumConverter {
public Number convert();
}
public class ByteArrayConverter {
#SuppressWarnings("unchecked")
public static Enum<?> convertToEnum(byte[] values, Class<?> fieldType, NumberSystem numberSystem) throws InvalidDataException {
if (values == null || values.length == 0) {
final String message = "The values parameter must contain the value";
throw new IllegalArgumentException(message);
}
if (!dtoFieldType.isEnum()) {
final String message = "dtoFieldType must be an Enum.";
throw new IllegalArgumentException(message);
}
if (!EnumConverter.class.isAssignableFrom(fieldType)) {
final String message = "fieldType must implement the EnumConverter interface.";
throw new IllegalArgumentException(message);
}
Enum<?> result = null;
Integer enumValue = (Integer) convertToType(values, Integer.class, numberSystem); // Our enum's use Integer or Byte for the value field.
for (Object enumConstant : fieldType.getEnumConstants()) {
Number ev = ((EnumConverter) enumConstant).convert();
if (enumValue.equals(ev)) {
result = (Enum<?>) enumConstant;
break;
}
}
if (result == null) {
throw new EnumConstantNotPresentException((Class<? extends Enum>) fieldType, enumValue.toString());
}
return result;
}
public static byte[] convertEnumToBytes(Enum<?> value, int requiredLength, NumberSystem numberSystem) throws InvalidDataException {
if (!(value instanceof EnumConverter)) {
final String message = "dtoFieldType must implement the EnumConverter interface.";
throw new IllegalArgumentException(message);
}
Number enumValue = ((EnumConverter) value).convert();
byte[] result = convertToBytes(enumValue, requiredLength, numberSystem);
return result;
}
public static Object convertToType(byte[] values, Class<?> type, NumberSystem numberSystem) throws InvalidDataException {
// some logic to convert the byte array supplied by the values param to an Object.
}
public static byte[] convertToBytes(Object value, int requiredLength, NumberSystem numberSystem) throws InvalidDataException {
// some logic to convert the Object supplied by the'value' param to a byte array.
}
}
Example of enum's:
public enum EnumIntegerMock implements EnumConverter {
VALUE0(0), VALUE1(1), VALUE2(2);
private final int value;
private EnumIntegerMock(int value) {
this.value = value;
}
public Integer convert() {
return value;
}
}
public enum EnumByteMock implements EnumConverter {
VALUE0(0), VALUE1(1), VALUE2(2);
private final byte value;
private EnumByteMock(int value) {
this.value = (byte) value;
}
public Byte convert() {
return value;
}
}
Just because the accepted answer is not self contained:
Support code:
public interface EnumWithCode<E extends Enum<E> & EnumWithCode<E>> {
public Integer getCode();
E fromCode(Integer code);
}
public class EnumWithCodeMap<V extends Enum<V> & EnumWithCode<V>> {
private final HashMap<Integer, V> _map = new HashMap<Integer, V>();
public EnumWithCodeMap(Class<V> valueType) {
for( V v : valueType.getEnumConstants() )
_map.put(v.getCode(), v);
}
public V get(Integer num) {
return _map.get(num);
}
}
Example of use:
public enum State implements EnumWithCode<State> {
NOT_STARTED(0), STARTED(1), ENDED(2);
private static final EnumWithCodeMap<State> map = new EnumWithCodeMap<State>(
State.class);
private final int code;
private State(int code) {
this.code = code;
}
#Override
public Integer getCode() {
return code;
}
#Override
public State fromCode(Integer code) {
return map.get(code);
}
}
given:
public enum BonusType {
MONTHLY(0), YEARLY(1), ONE_OFF(2)
}
BonusType bonus = YEARLY;
System.out.println(bonus.Ordinal() + ":" + bonus)
Output:
1:YEARLY
If you have a class Car
public class Car {
private Color externalColor;
}
And the property Color is a class
#Data
public class Color {
private Integer id;
private String name;
}
And you want to convert Color to an Enum
public class CarDTO {
private ColorEnum externalColor;
}
Simply add a method in Color class to convert Color in ColorEnum
#Data
public class Color {
private Integer id;
private String name;
public ColorEnum getEnum(){
ColorEnum.getById(id);
}
}
and inside ColorEnum implements the method getById()
public enum ColorEnum {
...
public static ColorEnum getById(int id) {
for(ColorEnum e : values()) {
if(e.id==id)
return e;
}
}
}
Now you can use a classMap
private MapperFactory factory = new DefaultMapperFactory.Builder().build();
...
factory.classMap(Car.class, CarDTO.class)
.fieldAToB("externalColor.enum","externalColor")
.byDefault()
.register();
...
CarDTO dto = mapper.map(car, CarDTO.class);