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-The example I'm going to use consists of a class called
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-ImageReaderFactory which provides the factory method which is this one;
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-createImageReader. As you can see the method takes an InputStream
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-as input and returns an object of type ImageReader, and it's
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-static so that we can invoke it even if we
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-don't have an instance of the ImageReaderFactory. So what does the
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-method do? Well the method first invokes, getImageType, passing the
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-InputStream as a parameter and this method figures out the type
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-of the image that is stored in this Inputstream and it's
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-an integer. Then, based on the value of this integer, the
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-method does one of several things. If the image type is
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-a GIF, it will invoke the constructor for GifReader passing the
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-stream as a parameter. And what will happen is that the
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-GIF reader will read a GIF from the stream, create a
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-corresponding object and return it. So in this case, the ImageReader
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-object return will be the object representing a GIF as appropriate.
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-Similarly, if the image type is JPEG, then the method will
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-invoke the constructor for JPEG Reader and in this case, this constructor
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-will read from the stream a JPEG, create a corresponding object
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-and return it. And so on for different types of images. So
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-why is this a situation in which it is appropriate to
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-use the factory method pattern? One, because it corresponds exactly to the
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-cases that we saw before, of applicability. This is a case
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-in which we don't know the type of the object that we
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-need to create until we run the code, because it depends
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-on the value of the InputStream. It depends on the content
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-of the InputStream. So, until we read the InputStream, we cannot
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-figure out whether we need to create a GIF, a JPEG or
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-some other type of image. So in this case, we want to
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-do, we want to simply delegate to this classes the creation of
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-the object, once we know what type of object needs to
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-be created. So perfect example of application of a factory method pattern.