java factory pattern question

Question

I'm currently using my factory like this:

public class AbstractFactory
{
    public static AbstractHeader parseHeader(File file)
    {
            if(AFactory.canRead(file))return AFactory.parseHeader(file);
            if(BFactory.canRead(file))return BFactory.parseHeader(file);

            throw new UnsupportedOperationException("File ["+file+"] not supported");
    }

    public static AbstractContent parseContent(AbstractHeader h)
    {
            if(h instanceof AHeader){
                    return AFactory.parseContent((AHeader) h);
            }
            if(h instanceof BHeader){
                    return BFactory.parseContent((BHeader) h);
            }
            throw new UnsupportedOperationException("Header not supported");
    }
}

the parseHeader() will return an instance of either AHeader or BHeader, and in a later time will ask for the AbstractContent. Is there a better way to do this ? Get away with the instanceof checks ?

+1 to Darron's answer. Also, a matter of style: AbstractFactory is not abstract, so the name is misleading. — Mike Baranczak
– Mike Baranczak, Commented Nov 8, 2010 at 19:31

Darron · Accepted Answer · 2010-11-08 18:36:19Z

5

Add the following code to your existing classes:

public abstract class AbstractHeader {
    abstract AbstractContent parseContent();
}

public class AHeader extends AbstractHeader {
    public AbstractContent parseContent() {
         return AFactory.parseContent((AHeader) h);
    }
}

public class BHeader extends AbstractHeader {
    public AbstractContent parseContent() {
         return BFactory.parseContent((AHeader) h);
    }
}

Now you can just call h.parseContent(). This is called polymorphism.

answered Nov 8, 2010 at 18:36

Darron

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2 Comments

helpermethod Over a year ago

+1 Nice and clean solution. Makes extending the class very easy.

Anon Over a year ago

off-course ! I was so blind with the factory idea that I didn't even thought of the simpler solution !

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