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abstract factory pattern

admin 11月 14, 2020 0


The pattern is best utilized when our system has to create multiple families of products or we want to provide a library of products without exposing the implementation details.

An example of an Abstract Factory in use could be UI toolkits. Across Windows, Mac and Linux, UI composites such as windows, buttons and textfields are all provided in a widget API like SWT. However, the implementation of these widgets vary across platforms. We could write a platform independent client thanks to the Abstract Factory implementation.

Intent

  • Provide an interface for creating a family of related objects, without explicitly specifying their concrete classes.
  • The new operator considered harmful.

Implementation

Class Diagram of Abstract Factory Pattern
Window is our AbstractProduct.

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public interface  {
    public void setTitle(String text);
    public void repaint();
}

This is our concrete product for Microsoft Windows.

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//ConcreteProductA1
public class MSWindow implements  {
    
    public void setTitle(String text) {
      //MS Windows specific behaviour
    }
    
    public void repaint() {
      //MS Windows specific behaviour
    }
}

This is our concrete product for Mac OSX.

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//ConcreteProductA2
public class MacOSXWindow implements  {
    
    public void setTitle(String text) {
      //Mac OSX specific behaviour
    }
    
    public void repaint() {
      //Mac OSX specific behaviour
    }
}

Now we need to provide our AbstractFactory.

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//AbstractFactory
public interface AbstractWidgetFactory {
    public Window createWindow();
}

Next we need to provide ConcreteFactory implementations for MS Windows.

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//ConcreteFactory1
public class MsWindowsWidgetFactory implements AbstractWidgetFactory {
    
    public Window createWindow() {
        //create an MSWindow
        MSWindow window = new MSWindow();
        return window;
    }
}

And for Mac OSX.

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//ConcreteFactory2
public class MacOSXWidgetFactory implements AbstractWidgetFactory {
    @Override
    public Window createWindow() {
        //create a MacOSXWindow
        MacOSXWindow window = new MacOSXWindow();
        return window;
    }
}

Here is our client to take advantage of all this functionality.

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//Client
public class Main{
    public static void main(String[] args) {
        AbstractWidgetFactory widgetFactory = null;
        //check what platform we're on
        if(Platform.currentPlatform()=="MACOSX") {
            widgetFactory  = new MacOSXWidgetFactory();
        } else {
            widgetFactory  = new MsWindowsWidgetFactory();
        }
        Window window = widgetFactory.createWindow();
        window.setTitle("New Window");
    }
}

Reference

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