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Factory Method Design Pattern in Java

In class-based programming, the factory method pattern is a creational pattern that uses factory methods to deal with the problem of creating objects without having to specify the exact class of the object that will be created. This is done by creating objects by calling a factory method—either specified in an interface and implemented by child classes, or implemented in a base class and optionally overridden by derived classes—rather than by calling a constructor.

interface ImageReader {
    DecodedImage getDecodeImage();
}

class DecodedImage {
    private String image;

    public DecodedImage(String image) {
        this.image = image;
    }

    @Override
    public String toString() {
        return image + ": is decoded";
    }
}

class GifReader implements ImageReader {
    private DecodedImage decodedImage;

    public GifReader(String image) {
        this.decodedImage = new DecodedImage(image);
    }

    @Override
    public DecodedImage getDecodeImage() {
        return decodedImage;
    }
}

class JpegReader implements ImageReader {
    private DecodedImage decodedImage;

    public JpegReader(String image) {
        decodedImage = new DecodedImage(image);
    }

    @Override
    public DecodedImage getDecodeImage() {
        return decodedImage;
    }
}

public class FactoryMethodDemo {
    public static void main(String[] args) {
        DecodedImage decodedImage;
        ImageReader reader = null;
        String image = args[0];
        String format = image.substring(image.indexOf('.') + 1, (image.length()));
        if (format.equals("gif")) {
            reader = new GifReader(image);
        }
        if (format.equals("jpeg")) {
            reader = new JpegReader(image);
        }
        assert reader != null;
        decodedImage = reader.getDecodeImage();
        System.out.println(decodedImage);
    }
}

Code examples

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