Pass java.lang.Object as Parameter

Question

I know that passing a an Object is not a good practise. But in this case it seems the best solution to me.

public void doSomething(final Object obj) {
    // some code
    ...
    if (obj instanceof InputStream) {
            document = PDDocument.load((InputStream) obj);
    } else if (obj instanceof File) {
        document = PDDocument.load((File) obj);
    } else {
        throw new IllegalArgumentException("Argument must be an instance of " + InputStream.class.getName() + " or " + " " + File.class.getName() + ".");
    // more code
    ...
    }
}

An alternative solution would have more duplicated code (all the line before and after PDDocument.load(obj);)

public void doSomething(final InputStream obj) {
    // some code
    ...
    document = PDDocument.load(obj);
    // more code
    ...
    }
}

public void doSomething(final File obj) {
    // some code
    ...
    document = PDDocument.load(obj);
    // more code
    ...
    }
}

Due to the duplicated code I prefer the first solution.

Do you know any better solution to solve this problem?

mix them up. have two separate methods that call a shared method with the duplicate code. — Stultuske
– Stultuske, Commented Sep 4, 2017 at 7:06

Andy Turner · Accepted Answer · 2017-09-04 07:33:44Z

6

Pass in the result of

PDDocument.load(specificallyTypedVariable)

as a parameter to the method.

This assumes that // some code isn't doing some kind of setup for the load call. If that's the case, you could pass in a Function<? super T, PDDocument> along with the T you're going to load it from:

public <T> void doSomething(final T obj, Function<? super T, PDDocument> loader) {
  // some code
  PDDocument document = loader.apply(obj);
  // other code.
}

and invoke like:

doSomething(someFile, PDDocument::load);
doSomething(someInputStream, PDDocument::load);

edited Sep 4, 2017 at 7:33

answered Sep 4, 2017 at 7:09

Andy Turner

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2 Comments

AxelH Over a year ago

I would use this idea, 3 methods (the two with specific param that will instanciate the document and call the third private accepting the PDDocument document that will have the full logic), simple and correctly typed. I guess this is your idea behing this answer.

Andy Turner Over a year ago

@AxelH the idea here is the Law of Demeter (principle of least knowledge). The method doesn't need to know if the document is loaded from a file, read from a stream etc: it just needs the document. It is notable how only passing the thing you need makes the code simpler (just 1 method required) and more flexible (you could doSomething to documents from a wider range of sources).

fge · Accepted Answer · 2017-09-04 07:16:21Z

1

Since PDDocument can load from an InputStream and you can obtain an InputStream from a File anyway, I'd suggest:

public void doSomething(final InputStream in)
{
    // some code
    document = PDDocument.load(in);
    // more code
}

public void doSomething(final File file)
{
    try (
        final InputStream in = new FileInputStream(file);
    ) {
        doSomething(in);
    } catch (IOException e) {
        throw new RuntimeException(e);
    }
}

Of course, handle errors accordingly!

Also, I don't understand why you don't return the document and put that processing in a method returning void?

edited Sep 4, 2017 at 7:16

answered Sep 4, 2017 at 7:11

fge

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4 Comments

Andy Turner Over a year ago

nit: "A variable declared in a resource specification is implicitly declared final (§4.12.4) if it is not explicitly declared final." Making it explicitly final is merely noise, IMO :)

Kayaman Over a year ago

Maybe add the "...some code..." parts to the InputStream overload to make it more clear as to how this reduces the code duplication.

Andy Turner Over a year ago

A slight variation on this idea would be: don't provide an overload for File at all: just make it so you've got to pass in an InputStream; caller can decide how to do that.

fge Over a year ago

@AndyTurner hmm... I didn't know that :) I'll remember that. I'm a little too much final-happy :)

ΦXocę 웃 Пepeúpa ツ · Accepted Answer · 2017-09-04 07:07:32Z

0

Move

// some code
...
document = PDDocument.load(obj);
// more code

to a separate private method which can only be called by the two above methods

edited Sep 4, 2017 at 7:07

ΦXocę 웃 Пepeúpa ツ

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answered Sep 4, 2017 at 7:06

Scary Wombat

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