What is a factory method

Can anyone tell me wat exactly is a factory method??

Native classs..
Java code cannot directly make calls to the local
operating system to access disk files, run programs,
use network resources, or query databases. Instead,
such requests must be made indirectly through a
native class. what's a native class, hot-chips?
To build a native class, the programmer starts with
Java code that defines the field variables and the
names and arguments of all methods. The methods
contain no code. This file is then processed by a
utility that converts it into C. The rest of the
programming is done with the native C language and
all the subroutines available through it. not a native class. there's no such thing. you mean native methods, hot-chips. a class can happily mix both java and native methods. Object.class, for example
other native languages than 'C' are available

Similar Messages

What is a Factory method and when to use this concept?

Could any one please describe what a factory method is and explain how I can use it by giving a simple example

A Factory Method (sometimes called a "virtual constructor") is a way to avoid hard coding what class is instantiated. Consider:
DataSource myDataSource = new DataSource();Now, if you want to use some other DataSource in your app, say, an XMLDataSource, then you get to change this code and all subsequent lines that use this, which can be a lot. If, however, you specified and interface for your DataSources, say, IDataSource, and you gave the DataSource class a static "create" method that would take some indication of what sort of DataSource to actually use, then you could write code like:
IDataSource myDataSource = DataSource.create(dataSourceString);And be able to pass in a dataSourceString describing what DataSource you wanted to use - and not have to recompile. Check out the Java Design Patterns site ( http://www.patterndepot.com/put/8/JavaPatterns.htm )
Make sense?
Lee

What is a factory method? when to use this concept?

Could any oneplease describe what a factory method is and explain how I can use it by giving a simple example?

Instead of instantiating a class all over your program you do it in one method that's part of the class. This means the class gets control over the instantiating process, a factory.
1. You can implement a dispose facility, that is giving back objects that can be reused (when the factory method is called an old object is returned if there is one in store, only if not a new one is instantiated).
2. An abstract class can have a factory method that returns concrete classes on demand, like
abstract class Hello {
   static newHello(int id) { // factory method
      switch (id) {
      case 0: return new Hi();
      case 1: return new Howdy();
      return null;
public class Hi extends Hello {
public class Howdy extends Hello {

Problem in factory method, how to pass arguments ?

Hello it's me again :)
here's the code :
package print;
import java.util.*;
import static print.Print.*;
interface Fact<T> {
T create(String n);;
T create ();
class PetColl {
      public String toString() {
      return getClass().getSimpleName();
      static List<Fact<? extends Pet>> petSpecies=
      new ArrayList<Fact<? extends Pet>>();
      static {
      // Collections.addAll() gives an "unchecked generic
      // array creation ... for varargs parameter" warning.
           petSpecies.add(new Cymric.Factory());
           petSpecies.add(new EgyptianMau.Factory());
           petSpecies.add(new Hamster.Factory());
           petSpecies.add(new Manx.Factory());
           petSpecies.add(new Mouse.Factory());
           petSpecies.add(new Pug.Factory());
           petSpecies.add(new Mutt.Factory());
           petSpecies.add(new Rat.Factory());
      private static Random rand = new Random(47);
      public static Pet createRandom() {
      int n = rand.nextInt(petSpecies.size());
      return petSpecies.get(n).create();
      public Pet[] createArray(int size) {
           Pet[] result = new Pet[size];
           for(int i = 0; i < size; i++)
           result[i] = createRandom();
           return result;
      public ArrayList<Pet> arrayList(int size) {
           ArrayList<Pet> result = new ArrayList<Pet>();
           Collections.addAll(result, createArray(size));
           return result;
class Individual implements Comparable<Individual> {
     private static long counter = 0;
     private final long id = counter++;
     private String name;
     public Individual(String name) { this.name = name; }
     // ?name? is optional:
     public Individual() {}
     public String toString() {
     return getClass().getSimpleName() +
     (name == null ? "" : " " + name);
     public long id() { return id; }
     public boolean equals(Object o) {
     return o instanceof Individual &&
     id == ((Individual)o).id;
     public int hashCode() {
     int result = 17;
     if(name != null)
     result = 37 * result + name.hashCode();
     result = 37 * result + (int)id;
     return result;
     public int compareTo(Individual arg) {
     // Compare by class name first:
     String first = getClass().getSimpleName();
     String argFirst = arg.getClass().getSimpleName();
     int firstCompare = first.compareTo(argFirst);
     if(firstCompare != 0)
     return firstCompare;
     //second compare by name
     if(name != null && arg.name != null) {
     int secondCompare = name.compareTo(arg.name);
     if(secondCompare != 0)
     return secondCompare;
     }//third compare by id
     return (arg.id < id ? -1 : (arg.id == id ? 0 : 1));
class Pets {
      public static final PetColl creator =
      //new LiteralPetCreator();
           new PetColl();
      public static Pet randomPet() {
      return creator.createRandom();
      public static Pet[] createArray(int size) {
      return creator.createArray(size);
      public static ArrayList<Pet> arrayList(int size) {
      return creator.arrayList(size);
class Person extends Individual {
String name;
public static class Factory implements Fact<Person>{
public Person create(String name){
     Person.name=name;
     return new Person(); }
public Person create(){return new Person();}
class Pet extends Individual {
class Dog extends Pet {
class Mutt extends Dog {
      public static class Factory implements Fact<Mutt> {
           public Mutt create(String name){return new Mutt(name);}
           public Mutt create () {return new Mutt();}
class Pug extends Dog {
      public static class Factory implements Fact<Pug> {
           public Pug create(String name){return new Pug(name);}
           public Pug create () {return new Pug();}
class Cat extends Pet {
class EgyptianMau extends Cat {
      public static class Factory implements Fact<EgyptianMau> {
           public EgyptianMau create(String name){return new EgyptianMau(name);}
           public EgyptianMau create () {return new EgyptianMau();}
      class Manx extends Cat {
           public static class Factory implements Fact<Manx> {
                public Manx create(String name){return new Manx(name);}
                public Manx create () {return new Manx();}
     class Cymric extends Manx {
          public static class Factory implements Fact<Cymric> {
                public Cymric create(String name){return new Cymric(name);}
                public Cymric create () {return new Cymric();}
class Rodent extends Pet {
class Rat extends Rodent {
      public static class Factory implements Fact<Rat> {
           public Rat create(String name){return new Rat(name);}
           public Rat create () {return new Rat();}
class Mouse extends Rodent {
      public static class Factory implements Fact<Mouse> {
           public Mouse create(String name){return new Mouse(name);}
           public Mouse create () {return new Mouse();}
class Hamster extends Rodent {
      public static class Factory implements Fact<Hamster> {
           public Hamster create(String name){return new Hamster(name);}
           public Hamster create () {return new Hamster();}
public class Test {
      public static void main(String[] args) {
          for(Pet p:Pets.creator.arrayList(25)){
      PetCount.petC.count(p.getClass().getSimpleName());
          print(p.getClass().getSimpleName());}
class PetCount {
      static class PetCounter extends HashMap<String,Integer> {
      public void count(String type) {
      Integer quantity = get(type);
      if(quantity == null)
      put(type, 1);
      else
      put(type, quantity + 1);
     public static PetCounter petC= new PetCounter();
}and here's my problem:
I'm trying to fill up list using factory method but in a fact that I want to have two constructors, I have a problem to set field name of objects of those classes. Is there any possibility to use in that way some factory method to create that list ?
In Person class I've tried to set it in factory method before creating an object, but as you know that option is only alvailable for static fields which i don't want to be static.

I for one have no idea what you're asking, and what you seem to be saying doesn't make sense.
I'm trying to fill up list using factory method but in a fact that I want to have two constructors,Two constructors for what? The factory class? The classes that the factory instantiates?
I have a problem
to set field name of objects of those classes. Is there any possibility to use in that way some factory method to
create that list ?What?
In Person class I've tried to set it in factory method before creating an object, but as you know that option is only alvailable for static fields which i don't want to be static.That doesn't make any sense. A Factory can easily set fields in the objects it creates on the fly (not static).

Meaning of factory method in abap objects

Hi,
Can anybody help me in understanding the meaning of factory method in abap object? what is the importance of this?
Regards
Sudhansu

Hi Krish and Sudhansu,
Design patterns are solutions which are already verified and known by many developers. That is why it is worth to use them. There is no need to reinvent the wheel in many cases.
I would recommend book which is placed in the ABAP world:
http://www.sap-press.com/products/Design-Patterns-in-Object%252dOriented-ABAP-(2nd-Edition).html
Although Java language has intuitive syntax, there are some special things in ABAP development so it is better to check solutions adjusted for ABAP editor.
The most common usage of factory pattern is to simplify object creation.
- By one method call you provide required parameters and do all initializations, including dependent objects.
- Class can have many factory methods, if you want to provide more ways of initialization.
- Factory method is usually static in the class and they return initialized instance of object for this class.
- There is naming convention to start factory method name with "create" - easy to recognize pattern.
- If you set property of class to "private instantiation" then you force to use factory method for object creation. In this way it is really simple to find all places where object are created with given set of input parameters - find references of factory method.
Factory pattern becomes even more powerful if we add inheritance. Factory method returns basic object (like ZCL_VEHICLE) but its implementation can return different subclass instance, depending on input parameter (ZCL_CAR, ZCL_TRAIN etc). Each instance can implement differently behavior (methods implementation), but these are object oriented techniques.
Regards,
Adam

Factory method

Hey all, I am tying to learn factory method and working on an example from the Oreilly AS3 Design patterns book. I am attempting figure out how all the classes work together in this design pattern and I have a question I am hoping someone might be able clearify for me.
In the document class "Main" I have the following code in the constructor
// instantiate concrete shape creators
var unfilledShapeCreator:ShapeCreator = new UnfilledShapeCreator( );
// draw unfilled shapes NOTE: draw() is a method of the ShapeCreator class
unfilledShapeCreator.draw(UnfilledShapeCreator.CIRCLE, this.stage, 50, 75);
I get what is going on there, so I open up the 'UnfilledShapeCreator" class and it has the following:
package shapecreators
     /* Concrete Creator class */
     public class UnfilledShapeCreator extends ShapeCreator
          public static const CIRCLE :uint = 0;
          public static const SQUARE :uint = 1;
          //implement the createShape factory method from the ShapeCreator Class.
          override protected function createShape(cType:uint):ShapeWidget
               if (cType == CIRCLE)
                    trace("Creating new circle shape");
                    return new CircleWidget( ); //Instantiates circleWidge Product Class
               } else if (cType == SQUARE) {
                    trace("Creating new square shape");
                    return new SquareWidget( ); //Instantiates square Widge Product Class
               } else {
                    throw new Error("Invalid kind of shape specified");
                    return null;
and the ShapeCreator class is as follows
package shapecreators
     /* Defines the abstract interface for the creator classes */
     import flash.display.DisplayObjectContainer;
     import flash.errors.IllegalOperationError;
     // ABSTRACT Class (should be subclassed and not instantiated)
     public class ShapeCreator
          public function draw(cType:uint, target:DisplayObjectContainer, xLoc:int, yLoc:int):void
               var shape = this.createShape(cType);
               shape.drawWidget( );
               shape.setLoc(xLoc, yLoc); // set the x and y location
               target.addChild(shape); // add the sprite to the display list
          // ABSTRACT Method (must be overridden in a subclass)
          protected function createShape(cType:uint):ShapeWidget
               throw new IllegalOperationError("Abstract method: must be overridden in a subclass");
               return null;
My question is: how does the cType parameter get passed into the createShape method? This method does not seem to get called from anywhere or any other class.   I see how FilledShapeCreator.CIRCLE gets passed to the draw method in the ShapeCreator class, but the createShape method is never called like the draw method is.
Is it because createShape is called within the draw function?
I am quite sure it is a simple answer, but it has me completely lost.
Thanks,

Yes, it is called by super class in line:
var shape = this.createShape(cType);
By the way, I don't know where you got code but it is a pretty bad practice not type variables. Good compiler should not even allow you to compile. The line above should be:
var shape:ShapeWidget = this.createShape(cType);

Factory method usage, creating the correct Image subclass

Hi, I created a factory method
public enum ImgType {
    SINGLE, STRIP, SPRITE_SHEET
public static Image createImage(ImgType imgType) {
    switch (imgType) {
      case SINGLE:
        return new MyImage1(0, 0);
      case SPRITE_SHEET:
        return new MyImage2("", 0, 0);
      case STRIP:
        return new MyImage3("", 0, 0);
      default:
        throw new IllegalArgumentException("The image type " + imgType + " is not recognized.");
}that creates different images based on the enum type provided.
and heres is a usage of that function
public BufferedImage loadAwtImage(ImageInputStream in, String imgName, ImageTypeFactory.ImgType imgType) throws IOException {
    BufferedImage img = imgLoader.loadImage(in);
    BufferedImage imgsubType = ImageTypeFactory.createImage(imgType); // Convert to real Image type
    addAwtImg(imgName, imgsubType);
    return imgsubType;
}In a test:
imgLib.loadAwtImage(imageStream, "cursor", ImageTypeFactory.ImgType.SPRITE_SHEET);Is it 'good' that in the test I can say(using the imgType enum) what sort of Image should be returned?
doesn't this expose the working of the class to the outside, on the other hand I don't know howto create the correct sub image based on an image loaded.
I use subImages to allow selection within the image, like the 3th 'tile' within an imageStrip returns just that cropped image.
Before I had List<Image> and List<List<Image>> and now I can just return Images in 1 method instead of 2,3 by using lists.
Edited by: stef569 on Dec 12, 2008 11:05 AM

creates specifications... :p
* load the BufferedImage from the ImageInputStream
* add it to the cache keyed by the imgName
* @return a BufferedImage, or a custom subclass based on the imgType
* @throws IOException when the img could not be loaded
public BufferedImage loadAwtImage(ImageInputStream in, String imgName, ImageTypeFactory.ImgType imgType) throws IOException I can test it, but the ImageTypeFactory.ImgType imgType parameter looks wrong to me.
if you see this in a class method would you change it/find a better way.

Static factory methods, instead of constructor

Hi All,
why we use static factory methods, instead of constructor.
Apart from Singleton class , what is use of static factory methods ?
Thanks in Advance,
Rishi

One reason for using factories is that they simplify creating instances of immutable classes that might otherwise have messy constructors with lots of arguments.

Factory method generateRandomCircle: "cannot resolve symbol"

I have written 2 classes: Point and Circle, which uses Point objects in order to create a Circle object. I have created a factory method for Point, which creates random Point objects and a for Circle, which does the same. "newRandomInstance" works fine for Point, but "generateRandomCircle" throws a "cannot resolve symbol" error. "main" is inside Point class. What's the problem?
Thanks
================================================
import java.io.*;
import java.lang.*;
import java.util.*;
public class Circle implements Cloneable
public static Circle generateRandomCircle()
int a= (int) (Math.random()* Short.MAX_VALUE);
int b= (int) (Math.random()* Short.MAX_VALUE);
Point p=new Point(a,b);
int r= (int) (Math.random()* Short.MAX_VALUE);
Circle c= new Circle(p,r);
return c;
===============================================
import java.io.*;
import java.lang.*;
import java.util.*;
public class Point implements Cloneable, Comparable
public static Point newRandomInstance()
int x = (int) (Math.random() * Short.MAX_VALUE);
int y = (int) (Math.random() * Short.MAX_VALUE);
return new Point(x,y);
public static void main (String[] args)
Circle cRandom= generateRandomCircle(); //doesn't work
System.out.println(cRandom.getCenter()+" "+ cRandom.getRadius());
Point randomP= newRandomInstance(); //works OK
randomP.printPoint();
}

I tried "Circle cRandom=
Circle.generateRandomCircle(); " instead of "Circle
cRandom= generateRandomCircle();" and it worked. Why
did this happen?Because generateRandomCircle() exists in class Circle and not in class Point where your are trying to use it.
>
Function "newRandomInstance()" works either as
"Point.newRandomInstance()" or as
"newRandomInstance()", however. Why does this
controversy exist?No controversy! Your main() is contained within class Point and as such knows about everything that is declared in class Point() but nothing about what is in class Circle unless you tell it to look in class Circle.

Design Patterns: 'Program to an interface, not an impl.' and Factory Method

Design Patterns: 'Program to an interface, not an implementation' and Factory Method.
Hi All,
I've 4 questions. And 1M thanks for your precious input.
1. OOAD steps:
Requirement-->Use Cases-->Analysis Classes-->Sequence Diagrams-->CRC-->other UML diagrams if needed--> Domain/Business Classes.
If we follow the rule 'Program to an interface, not an implementation',
would that imply NECESSARILY we should have another set of Interface Classes for our Domain Classes? i.e Interface_ClassX for ClassX_Impl.
2. If the point 1 is a MUST because of the rule 'Program to an interface, not an implementation',
ie we should have an Interface classe for every one Domain classe,
would that NECESSARILY imply we should have as many Factory Methods as they are Domain Classes to abstract the creation process?
Interface_ClassX X= Factory.GetClassX() ( return new ClassX_Impl)
Interface_ClassY Y= Factory.GetClassY() ( return new ClassY_Impl)
Interface_ClassZ Z= Factory.GetClassZ() ( return new ClassZ_Impl)
3. On the point 2, the underlying principle used is Factory Methods.
Now on the surface, what are other possible business and/or technical naming for such Factory Methods? I mean should we call it a kind of Business Facade?
4. Is the point 1 and point 2 considered to be the best practices?

So the question here is whether we can predict having
more than one possible implementations which required
option c. Is this a dilema? I guess it's hard to
predict the future.Right. Hopefully it's fairly obvious while designing things and
deciding what objects are needed.
Now, if the Presentation Tier, says JSP, needs that
ClassNormal object. Would we still keep that line of
code a.
OR would we introduce an intermediate object to free
JSP from the direct creational aspect using new
keyword like the choice b. that you reject.
The point here is to reduce the direct coupling aspect
between the Presentation Tier and Business Tier. So
what would that intermediate object be?In that case, you have to ask yourself if there is a valid
need for reducing the coupling. If you simply make an intermediate
object, what keeps you from making an intermediate object to your
new intermediate object, ad infinitum.
That intermediate object could be a Facade pattern, or simply
an abstraction. We actually did that here, we began a massive
java project, and we abstracted away from Swing J-classes and created
our own "wrappers" that simply extended all the J-classes and we had
all our programmers develop using our wrappers instead of the Swing
classes. That allowed us to add some custom code, some temporary bug fixes, etc. Some of our classes were nothing more than "EPPasswordField extends JPasswordField" with nothing overridden. It does allow us a place to hook in and adjust or fix things if needed though.

Coloring an single field of an ALV using factory method

how can we color just a single field in ALV using factory method.

Hello Regi you may want to check this sample code, basically what you need is to use the lvc_s_colo structure and the set_color method of the class cl_salv_column_table.
METHOD set_colors.
*.....Color for COLUMN.....
    DATA: lo_cols_tab TYPE REF TO cl_salv_columns_table,
          lo_col_tab TYPE REF TO cl_salv_column_table.
    DATA: ls_color TYPE lvc_s_colo.    " Colors strucutre
*   get Columns object
    lo_cols_tab = co_alv->get_columns( ).
    INCLUDE <color>.
*   Get ERDAT column & set the yellow Color fot it
    TRY.
        lo_col_tab ?= lo_cols_tab->get_column( 'ERDAT' ).
        ls_color-col = col_total.
        lo_col_tab->set_color( ls_color ).
      CATCH cx_salv_not_found.
    ENDTRY.
*.......Color for Specific Cell & Rows.................
*   Applying color on the 3rd Row and Column AUART
*   Applying color on the Entire 5th Row
    DATA: lt_s_color TYPE lvc_t_scol,
          ls_s_color TYPE lvc_s_scol,
          la_vbak    LIKE LINE OF ct_vbak,
          l_count    TYPE i.
    LOOP AT ct_vbak INTO la_vbak.
      l_count = l_count + 1.
      CASE l_count.
*       Apply RED color to the AUART Cell of the 3rd Column
        WHEN 3.
          ls_s_color-fname     = 'AUART'.
          ls_s_color-color-col = col_negative.
          ls_s_color-color-int = 0.
          ls_s_color-color-inv = 0.
          APPEND ls_s_color TO lt_s_color.
          CLEAR ls_s_color.
*       Apply GREEN color to the entire row # 5
*         For entire row, we don't pass the Fieldname
        WHEN 5.
          ls_s_color-color-col = col_positive.
          ls_s_color-color-int = 0.
          ls_s_color-color-inv = 0.
          APPEND ls_s_color TO lt_s_color.
          CLEAR ls_s_color.
      ENDCASE.
*     Modify that data back to the output table
      la_vbak-t_color = lt_s_color.
      MODIFY ct_vbak FROM la_vbak.
      CLEAR la_vbak.
      CLEAR lt_s_color.
    ENDLOOP.
*   We will set this COLOR table field name of the internal table to
*   COLUMNS tab reference for the specific colors
    TRY.
        lo_cols_tab->set_color_column( 'T_COLOR' ).
      CATCH cx_salv_data_error.                         "#EC NO_HANDLER
    ENDTRY.
ENDMETHOD.                    "set_colors

Static Factory Methods

can anybody guide me on what static factory methods are, how they are invoked and there advantages over constructors.

Joshua Bloch has a good bit on it in his book Effective Java. If you don't have that then I suggest Google as it's been explained to death before. Static factory methods are for all intents and purposes when you provide a static method that returns an instance of a given object rather than having a public constructor.

Singleton - Why have a factory method?

Question:
Why bother to have a factory method [represented by getServiceFacade() below] for a singleton? Accessing any of the static methods in the singleton causes class instantiation.
In other words, what advantage is there to invoking a method with ServiceFacade.getServiceFacade().method() vs. ServiceFacade.method() ???
public final class ServiceFacade
private static ServiceFacade serviceFacade = new ServiceFacade();
// Constructor for the ServiceFacade
private ServiceFacade()
Log.info("ServiceFacade.ServiceFacade(): enter");
try
initializeServices();
catch (Exception e)
Log.error("ServiceFacade.ServiceFacade() Exception: static class not initialized.");
Log.info("ServiceFacade.ServiceFacade(): exit");
//public static ServiceFacade getServiceFacade()
// Log.info("ServiceFacade.getServiceFacade(): enter/exit");
// return serviceFacade;
private static synchronized void initializeServices()
throws ValidationException, MarshalException, IOException
// A bunch of stuff here ...

The idea behind a Singleton is that it allows some in-memory caching of state, since once a Singleton is instantiated, it stays in memory (being self-referential) as long as the JVM runs. Generally, the only static method is the "getInstance" (or in your case "getServiceFacade").
During the initialization, the Singleton factory will typically perform a lot of "expensive" operations (e.g. JNDI lookups, establishing connection pools, etc.) and then hold on to this information, so that it doesn't have to do it again, making all subsequent operations that much faster.

Could someone explain the Factory Method Design Pattern

Hi Experts.
Could someone please explain for me the Factory Method Design Pattern. I read it a little and I understand that it is used in JDBC drivers but i'm not clear on it.
Could someone explain.
Thanks in advance
stephen

Basically, you have one class that's sole purpose is to create instances of a set of other classes.
What will usually happen is you have a set of related classes that inherit from some base class. We'll say for example that you have a base class CAR and it has sub-classes FORD, GM, HONDA (sorry Crylser). Instead of having the user call the constructors for FORD, GM, and HONDA, you can give the user a Factory Class that will give him a copy. We'll call our factory class Dealership. Inside dealership, you can have a static function :
public static Car makeCar(String type)
if(type.equals("FORD")
return new FORD();
else if(type.equals("GM")
return new GM();
else if(type.equals("HONDA")
return new HONDA();
So when the user needs a car, they will just call
Dealership.makeCar("FORD").
This is a good way to hide the implementation of your classes from the user, or if you require complex initialization of your objects.
Another good example of this is in the Swing library. To get a border around a component, you call static methods on BorderFactory.
Hope this helped.
Ed

Constructor or factory method?

Hi!
This is probebly a wery simple problem but i havn't found a good answer.
I have a class that read/write to a specified file on disk. If an object hasn't existed before i want to pas a filename to create the object. When the object has already existed and already has an file on disk i also whant to get an instance of the object by passing in a file.
Both cases the constructor taks the same argument but i realy need tow seperate constructors. What should i do? Is there any pattern on this issue? Maby one of the constructors should be a factory method?
Thanks!
/Christer

If I am understanding you question correctly, you definitely want a factory. Don't have any public constructors. Here's an example that you can adapt as needed.
public final class FileFactory
   private static final Map files = new HashMap();
   private FileFactory(){}
   public static File getFile(String name)
      File file = files.get(name);
      if (file == null)
         file = new File(name);
         files.put(name, file);
      return file;
}If you want to sometimes return an existing instance, a constructor cannot possibly work for you. Constructors only return new instances.

What is a factory method

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