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);
Related
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)
I have to define the class below in ESPER so I'm able to reference the sub-types and internal arrays. I have to do it pragmatically. I don't care how:
UPDATE: The complete class:
public class IoTEntityEvent implements java.io.Serializable {
private IoTProperty[] Properties;
private String About;
IoTEntityEvent (){
this.About = null;
this.Properties = null;
}
public String getAbout() {
return About;
}
public void setAbout( String value){
this.About = value;
}
public void setProperties(int index, IoTProperty value) {
Properties[index] = value;
}
public IoTProperty getProperties(int index) {
return Properties[index];
}
public void setProperties( IoTProperty[] value) {
Properties = value;
}
public IoTProperty[] getProperties() {
return Properties;
}
}
This is the sub-class:
public class IoTProperty implements java.io.Serializable {
private Map<String,String>[] IoTStateObservation =null;
private String About = null;
IoTProperty (){
this.About = null;
this.IoTStateObservation = null;
}
public String getAbout() {
return About;
}
public void setAbout(String value) {
About = value;
}
public Map<String,String>[] getIoTStateObservation() {
return IoTStateObservation;
}
public void setIoTStateObservation( Map<String,String>[] value) {
IoTStateObservation = value;
}
public Map<String,String> getIoTStateObservation(int index) {
return IoTStateObservation[index];
}
public void setIoTStateObservation(int index, Map<String,String> value) {
IoTStateObservation[0] = value;
}
}
I tried like this :
eventNames[0] = "About";
eventType[0] = String.class;
eventNames[1] = "Properties";
eventType[1] = IoTProperty[].class;
epService.getEPAdministrator().getConfiguration().addEventType("type", eventNames, eventType);
This works but I can't access the sub-types. I also tried to define the sub type in similar manner. Can someone can explain how I suppose to do it?
What do you mean with "This works but I can't access the sub-types."
Tried like "select Properties[0].whatever" from type?
According to the Esper documentation:
Plain-old Java object events are object instances that expose event properties through JavaBeans-style getter methods. Events classes or interfaces do not have to be fully compliant to the JavaBean specification; however for the Esper engine to obtain event properties, the required JavaBean getter methods must be present or an accessor-style and accessor-methods may be defined via configuration.
In short, you need to create the JavaBean getters and setters in order to access your private members.
Thank you for the help. I found out how and is as following:
epService.getEPAdministrator().getConfiguration().addEventType("type",IoTEntityEvent.class);
Then the event should be send like this without any casting:
IoTValue[] va= {new IoTValue("0.62","2014-06-09T18:08:40.968Z","2014-06-09T18:08:40.968Z")};
IoTProperty[] pr = {new IoTProperty(va,"property")};
IoTEntityEvent event = new IoTEntityEvent(pr,"Entity");
epService.getEPRuntime().sendEvent(event);
I'm looking for ways to implement and access my enum and I'm not very happy with how nice the code looks. It seems like a patched way. So here is what I'm trying to do:
Consider this simple enum as an example of what I'm trying to do:
public enum MyEnum {
FIRST(0L), SECOND(1L), THIRD(2L);
private Long number;
private MyEnum(Long number){
this.number= id;
}
public static boolean isFirst(MyEnum type) {
return type == FIRST;
}
public static boolean isSecond(MyEnum type) {
return type == SECOND;
}
public static boolean isThird(MyEnum type) {
return type == THIRD;
}
public Long getId() {
return number;
}
}
Later on, I have some objects that I set as Long.valueOf(1L), and compare them with this enum using
Long.valueOf(1L).equals(instanceOfMyEnum.getId())
I really hate having those hardcoded constants all over my code so I was wondering if it's a bad practice to use something like this instead:
eMyEnum.FIRST.getId().equals(instanceOfMyEnum.getId())
or
someLongThatIPassAsParameter = eMyEnum.FIRST.getId();
These are just some simple examples but basically it's the same problem repeated over and over. What do you think?
If you have a lots of enum values, i would do something like this (No need to modify the code if you add new ones):
public enum MyEnum {
FIRST(0L), SECOND(1L), THIRD(2L);
private Long number;
/**
* Lookup map, to provide a quick way to access your enums by id
*/
private static final Map<Long, MyEnum> LOOKUP = new HashMap<Long, MyEnum>();
/**
* Static initializer, which loads your enums values runtime, and maps them
* to their 'number' member.
*/
static {
MyEnum[] enums = MyEnum.class.getEnumConstants();
for(MyEnum en : enums){
LOOKUP.put(en.number, en);
}
}
private MyEnum(final Long number) {
this.number = number;
}
/**
* Gets the enum value associated with the parameter, id.
* #param id The id, that identifies your enum value
* #return The enum value, or null, if not found.
*/
public static MyEnum getById(final Long id){
return LOOKUP.get(id);
}
}
Im not sure if I understood your question correctly, but what about using switch for the checks this for the checks?
public enum MyEnum {
FIRST(0L), SECOND(1L), THIRD(2L);
private Long number;
private static Map<Long, MyEnum> byIds = new HashMap<Long, PlaceServiceV2.MyEnum>();
static{
for(MyEnum myEnum :MyEnum.values()){
byIds.put(myEnum.number, myEnum);
}
}
private MyEnum(Long number){
this.number = number;
}
public static MyEnum getById(Long id) {
return byIds.get(id);
}
public Long getId() {
return number;
}
}
public void test(){
switch (MyEnum.getById(1L)) {
case FIRST:
break;
case SECOND:
break;
default:
break;
}
}
Why not implement a fromLong method in the enum
public static MyEnum fromLong(long l) {
switch (l) {
{
case 0: return FIRST;
case 1: return SECOND;
case 2: return THIRD;
}
throw new IllegalArgumentException();
}
and then convert longs to the enum and compare enums. So you would have:
MyEnum.fromLong(longValue) == MyEnum.FIRST
Apparently although you created an enum, your are still using these Long values everywhere, so maybe you can just use something like:
public class TypeOfSomething {
public static final long FIRST = 1l;
public static final long ANALOG = 2l;
public static final long USB = 3l;
}
and then use them like:
someLongThatIPassAsParameter = TypeOfSomething.ANALOG;
enum way is also fine, but I use it in case where it is more comfortable to use enum values in parameters, and value within enum is just additional information (e.g. messages.properties keys for internationalisation)
Im quite new to Java and this might be a basic doubt. But please help.
I have a class as below:
public class EnterLeaveHandler implements IOtfHandler {
public void handle(java.lang.Object ... args) {
long time = (Long) args[0];
int func = (Integer) args[1];
int cpuid = (Integer) args[2];
int source = (Integer) args[3];
}
I have another class:
public class DefFunctionHandler implements IOtfHandler {
public void handle(Object... args) {
int stream = (Integer) args[0];
int func = (Integer) args[1];
String name = (String) args[2];
int funcgroup = (Integer) args[3];
int source = (Integer) args[4];
}
}
So like you can see..there are 2 different classes, which have the same method, but receive different data. I need to get an input from the user for the "String name" in DefFunctionHandler class, and I identify the given name with the name in the file that I have...then correlate it with other data in the method like funcgroup and func. The same func is there in the other class too. So I need to make a comparison between them to get the data in the other class like time, etc.
So the data in the methods can be compared to the data structure in C...how do I implement such a structure in Java? I read that structs are similar to classes in Java. But in my case, I have the data in methods and not classes. Please tell me how to solve this problem.
To Answer Your Original Question
Long story short, you can't access method variables externally. What you want to do is make those variables fields within the class. Putting them outside the method means they stick around after the method is done, and it means you can access them from outside.
public class EnterLeaveHandler implements IOtfHandler {
private long time;
private int func;
private int cpuid;
private int source;
// Please don't use varargs like this; read the whole answer!!
public void handle(Object ... args) {
time = (Long) args[0];
func = (Integer) args[1];
cpuid = (Integer) args[2];
source = (Integer) args[3];
}
}
Then you access them by creating getters and setters:
public long getTime() {
return time;
}
public void setTime(long t) {
time = t;
}
// etc...
HOWEVER, Some Suggestions...
Your code is... strange, to say the least. It's also very non-Java-like. As much as possible, you should try to avoid having multiple overriding methods that need different data. Also, you normally want to initialize your fields in the constructor, not in some other method.
It's not clear how much of the code you have access to, but if you're able to rewrite the interface, I would definitely do so. Object varargs in an interface is just weird. The reason for using an interface is so that you can call an interface method with identical parameters and, regardless of the object type underneath, something useful will happen. It defeats the point of the interface to have two implementations of the same method require totally different arguments. The following code demonstrates why this is:
IOtfHandler h1 = new EnterLeaveHandler();
IOtfHandler h2 = new DefFunctionHandler();
h1.handle(0, 0, 0, 0);
h2.handle(0, 0, 0, 0); // Crashes with ClassCastException!! :(
// And would also crash two lines later with ArrayIndexOutOfBoundsException
Much better to just make them different methods entirely.You know what variables you're expecting, so you should take advantage of that fact. Your method signatures would be far better off looking something like this:
public class EnterLeaveHandler implements IOtfHandler {
public void handle(long time, int func, int cpuid, int source) {
// Do things with your shiny new variables
}
public class DefFunctionHandler implements IOtfHandler {
public void handle(int stream, int func, String name, int funcgroup, int source) {
// Do things with your shiny new variables
}
}
As others have suggested, if the "real" method signatures are not identical, you shouldn't be using an interface. Better to use an abstract base class instead, to hold what little data is common between them:
abstract class IOtfHandler {
private int source;
private int func;
public void setSource(int source) {
this.source = source;
}
// etc
}
class EnterLeaverHandler extends IOtfHandler {
private long time;
// etc
}
class DefFunctionHandler extends IOtfHandler {
private String name;
// etc
}
Of course, if you set all the variables in the constructors, you may be able to add an abstract handle() method to the base class, since then that method should have the same signature, and take no arguments at all!
Final Result
So if we pull together all the changes I've talked about-- moving the method variables into fields, using getters and setters, using useful method signatures, using constructors, and using a base class instead of a misleading interface, we end up with something like this:
abstract class IOtfHandler {
private int source;
private int func;
public void setSource(int source) {
this.source = source;
}
public int getSource() {
return source;
}
public void setFunc(int func) {
this.func = func;
}
public int getFunc() {
return func;
}
// abstract handle method
abstract public void handle();
}
class EnterLeaverHandler extends IOtfHandler {
private long time;
private int cpuid;
// getters and setters
public void setTime(long time) {
this.time = time;
}
public long getTime() {
return time;
}
public void setCpuId(int cpuid) {
this.cpuid = cpuid;
}
public int getCpuId() {
return cpuid;
}
// constructor
public EnterLeaverHandler(long time, int cpuid, int source, int func) {
setTime(time);
setCpuId(cpuid);
setSource(source);
setFunc(func);
}
// handle method
public void handle() {
System.out.println("EnterLeaverHandler.handle()");
// Do whatever class-specific handling you might want to do in here.
}
}
class DefFunctionHandler extends IOtfHandler {
private String name;
private int funcGroup;
private int stream;
// getters and setters
public void setName(String name) {
this.name = name;
}
public String getName() {
return name;
}
public void setFuncGroup(int funcGroup) {
this.funcGroup = funcGroup;
}
public int getFuncGroup() {
return funcGroup;
}
public void setStream(int stream) {
this.stream = stream;
}
public int getStream() {
return stream;
}
// constructor
public DefFunctionHandler(String name, int funcGroup, int stream, int source, int func) {
setName(name);
setFuncGroup(funcGroup);
setStream(stream);
setSource(source);
setFunc(func);
}
// handle method
public void handle() {
System.out.println("DefFunctionHandler.handle()");
// Do whatever class-specific handling you might want to do in here.
}
}
public class Main {
public static void main(String[] args) {
IOtfHandler h1 = new DefFunctionHandler("name", 0, 0, 0, 0);
IOtfHandler h2 = new EnterLeaverHandler(0, 0, 0, 0);
h1.handle();
h2.handle();
}
}
In order to make the variables class variables, all you have to do is move their declaration outside of the method. In other words, your code for the EnterLeaveHandler might look like this:
public class EnterLeaveHandler implements IOtfHandler {
long time;
int func;
int cpuid;
int source;
public void handle(java.lang.Object ... args) {
time = (Long) args[0];
func = (Integer) args[1];
cpuid = (Integer) args[2];
source = (Integer) args[3];
...
}
}
Create an abstract super class for your classes. Extend this with your classes and init the parameters in the handle call.
public abstract class AbstarctFunctionHandler implements IOtfHandler {
long time;
int func;
int cpuid;
int source
//add getters and setters, if you fancy
public boolean equals(AbstarctFunctionHandler obj){
//compare variables
return true;
}
}
You need to restructure your objects to have proper constuctors and setters/getters
This gives the benefit of protecting all your private variables and forcing other classes to adhere to your classe's "contract" by only allowing them to access it's inner variables via those setters/getters and constructor. Now you just instantiate the object, then use ti's methods to manipulate it.
Here is an example from your first example class:
public class EnterLeaveHandler implements IOtfHandler {
private long time;
private int func, cpuid, source;
public EnterLeavehandler(long time, int func, int cpuid, int source) {
this.time = time;
this.func = func;
this.cpuid = cpuid;
this.source = souce;
}
public long getTime() {
return this.time;
}
public void setTime(long time) {
this.time = time;
}
public int getFunc() {
return this.func;
}
public void setFunc(int func) {
this.func = func;
}
public int getCPUID() {
return this.cpuid;
}
public void setCPUID(int cpuid) {
this.cpuid = cpuid;
}
public int getSource() {
return this.source;
}
public void setSource(int source) {
this.source = source;
}
public void handle(long t, int f, int c, int s) {
this.setTime(t);
this.setFunc(f);
this.setCPUID(c);
this.setSource(s);
}
}
The best solution I could think of
1. is create a getter and setter
public void setName(String name) {
this.name = name;
}
public String getName() {
return name;
}
http://docs.oracle.com/javaee/6/tutorial/doc/gjbbp.html
2.create a wrapper method to do the comparsion prior to calling the individual method.
Hope this helps you.
I have Java bean class and I want to sort list of these beans by one bean attribute that is of String type. How can I do that?
Either make the type itself implement Comparable<Foo>, implementing the compareTo method by comparing the two strings, or implement a Comparator<Foo> which again compares by the strings.
With the first approach, you'd then just be able to use Collections.sort() directly; with the second you'd use Collections.sort(collection, new FooComparator());
For example:
public class Foo {
public String getBar() {
...
}
}
public class FooComparatorByBar implements Comparator<Foo> {
public int compare(Foo x, Foo y) {
// TODO: Handle null values of x, y, x.getBar() and y.getBar(),
// and consider non-ordinal orderings.
return x.getBar().compareTo(y.getBar());
}
}
By using a custom Comparator?
import java.util.*;
class Bean {
public final String name;
public final int value;
public Bean(final String name, final int value) {
this.name = name;
this.value = value;
}
#Override
public String toString() {
return name + " = " + value;
}
}
public class SortByProp {
private static List<Bean> initBeans() {
return new ArrayList<Bean>(Arrays.asList(
new Bean("C", 1),
new Bean("B", 2),
new Bean("A", 3)
));
}
private static void sortBeans(List<Bean> beans) {
Collections.sort(beans, new Comparator<Bean>() {
public int compare(Bean lhs, Bean rhs){
return lhs.name.compareTo(rhs.name);
}
});
}
public static void main(String[] args) {
List<Bean> beans = initBeans();
sortBeans(beans);
System.out.println(beans);
}
}
Using Guava, it's just
Collections.sort(list, Ordering.natural().compose(Functions.toStringFunction()));