Where to create AbstractFactory

Question

In an abstract factory, you declare a type that is responsible for creating objects.

This will prevent the need to use such a switch:

 if( type == ONE ) {
     doOne();
  } else if( type == TWO ) { 
     doTwo();
  } etc. 

Or the same thing:

 switch( type ) {
     case ONE: doOne(); break;
     case TWO: doTwo(); break;
     etc....
  }

In it:

   MyAbstractFactory factoryInstance = ... ? 

   SomeObject object = factoryInstance.createObject();

   object.doX();

As I understand it, AbstractFactory will create the correct object, which in turn will perform the polymorphically correct behavior.

Then, if you use this object 10-20 or 100 times in your program, you do not need to repeat this switch every time. You simply execute the appropriate method and leave the polymorphism to do this work.

   object.doY();

   object.doZ();

Adding a new type is as simple as creating a new concrete factory.

All this is clear to me. But...

Where and how is a specific factory created (in general terms)?

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:)

Answer 1

An Factory factory . , . , "Abstract Factory" " ", factory .

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VehicleFactory carFactory = new CarFactory();
IVehicle car = new Car(carFactory);

VehicleFactory truckFactory = new TruckFactory();
IVehicle truck = new Truck(truckFactory);

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public static ImageReader getImageReader(InputStream is) {    

 int imageType = figureOutImageType(is);

   switch(imageType) {
            case ImageReaderFactory.GIF:
                return new GifReader(is);
            case ImageReaderFactory.JPEG:
                return new JpegReader(is);
            // etc.
        }
}

Abstract factory Pattern, .

public static GUIFactory createOsSpecificFactory() {
        int sys = readFromConfigFile("OS_TYPE");
        if (sys == 0) {
            return new WinFactory();
        } else {
            return new OSXFactory();
        }
    }

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Answer 2

, factory , (, , factory ) . - "FactoryService", factory .

:

FactoryService service = FactoryService.instance();
MyAbstractFactory factory = service.getFactory();
SomeObject obj = factory.createObject();

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: factory . - -factory, .

Answer 3

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- Enum, , .

Answer 4

, , AbstractFactory.

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Answer 5

Using some IoC frameworks in this case is the most flexible solution - Spring was recommended in earlier answers, Google Guice is another great choice to get started with.

However, if a clean Java solution is required, the enumerations work really great. Pls will consider the following example:

enum FactoryConfig {
  CONFIG_1 {
     IFactory instantiate() {
        return ...
     }
  },
  CONFIG_2 {
     IFactory instantiate() {
        return ...
     }
  },
  CONFIG_3 {
     IFactory instantiate() {
        return ...
     }
  };

  abstract IFactory instantiate();
}
...
// and its usage..

IFactory factory = FactoryConfig.CONFIG_3.instantiate();

More information on the similar use of enumerations can be found, for example, here and.