Java design pattern: abstract factory pattern

1. Scene description

Connected with "Java Design Pattern (I) Factory Pattern"

One disadvantage of the factory model is that it destroys the principle of closedness of the class. For example, if you need to add data collection for Word files, follow the following steps:

• Create Word file data acquisition class to realize instrument data acquisition interface;
• Modify the instrument data acquisition factory category and add factory methods for Word file data acquisition;
• Call the factory class word file method;
  

Step 2 modified the factory class. If the factory class needs to be modified for each additional implementation class, then this is unreasonable.

The solution is to use abstract factory classes, create its factory class for each implementation class, and add factory interfaces so that each factory class implements the interface.

After using the abstract factory, the above steps are changed to:

• Create Word file data acquisition class to realize instrument data acquisition interface;
• Create a factory class for Word file data collection. This class implements factory interface and interface method to create a Word file data collection class;
• Get the factory class object of the Word file data collection class, and call the factory interface method, create the class object, and then call its method.
  

After modification, since the factory class is abstracted and the factory interface is defined, the original code is no longer necessary to be modified when adding the new implementation class, and the original implementation is not destroyed.

As shown in the figure below:

2. Sample code

Instrument data acquisition interface:

 package lims.designpatterndemo.abstractfactorydemo;public interface EquipmentDataCapture { public String capture(String filePath);}

PDF file collection class:

 package lims.designpatterndemo.abstractfactorydemo;public class PdfFileCapture implements EquipmentDataCapture{ @Override public String capture(String filePath) { return "PDF file content"; }}

Excel file collection class:

 package lims.designpatterndemo.abstractfactorydemo;public class ExcelFileCapture implements EquipmentDataCapture{ @Override public String capture(String filePath) { return "Excel File Content"; }}

Abstract factory, i.e. factory interface:

 package lims.designpatterndemo.abstractfactorydemo;public interface EquipmentDataCaptureFactory { public EquipmentDataCapture getCapture(); }

PDF file collection factory:

 package lims.designpatterndemo.abstractfactorydemo;public class PdfFileCaptureFactory implements EquipmentDataCaptureFactory { @Override public EquipmentDataCapture getCapture() { return new PdfFileCapture(); }}

Excel file collection factory:

 package lims.designpatterndemo.abstractfactorydemo;public class ExcelFileCaptureFactory implements EquipmentDataCaptureFactory { @Override public EquipmentDataCapture getCapture() { return new ExcelFileCapture(); }}

Call example:

 package lims.designpatterndemo.abstractfactorydemo;public class AbstractFactoryDemo { public static void main(String[] args) { EquipmentDataCaptureFactory fabric = new PdfFileCaptureFactory(); fabric = new ExcelFileCaptureFactory(); EquipmentDataCapture capture = fabric.getCapture(); String fileContent = capture.capture(""); System.out.println(fileContent); }}

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