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Re: How to extend FilterInputStream to convert tabs to spaces?

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On 3/8/2015 9:47 AM, fangyuncn@gmail.com wrote:
> Hi, I need to write a class Tabs2SpaceInputStream, it extends java.io.FilterInputStream. the code snippet like this:
>
> public class Tabs2SpaceInputStream extends FilterInputStream {
>
> 	/**
> 	 * @param in
> 	 */
> 	public Tabs2SpaceInputStream(InputStream in) {
> 		super(in);
> 	}
>
> 	@Override
> 	public int read() throws IOException {
> 		// TODO Auto-generated method stub
> 	}
>
> 	@Override
> 	public int read(byte[] b) throws IOException {
> 		// TODO Auto-generated method stub
> 	}
>
> 	@Override
> 	public int read(byte[] b, int off, int len) throws IOException {
> 		// TODO Auto-generated method stub
> 	}
> 	
> }
>
> This class is used to convert tabs to space when the under inpustream is read. Who give some help about this issue? Thanks a lot!.

     Because this has the scent of homework about it I won't offer a
fully-worked-out solution, nor even a code sketch.  But here are a
few observations and hints that might get you started:

     - Are you really sure you want to extend FilterInputStream for
this job?  I suspect FilterReader would be a better choice (which
would, of course, involve a different set of read() methods).

     - To decide how many spaces a tab should expand to, you'll need
to keep track of the current horizontal position.  So: That's one of
the state variables the class requires.

     - Keeping track of the horizontal position requires detecting
the ends of line so you know when to reset the position to zero.

    - You'll also need to know the positions at which the tabs are
set: Every eight spaces, or every four, or at columns 10,15,35,...
So: That's another state variable.

     - For simplicity's sake I'd be inclined to supply the tab positions
(or width) as a constructor parameter; changing the tabs on the fly
could get complicated, and I'd provide for it only if you're pretty sure
you'll need it.  So, this state "variable" might actually be a `final'.

     - Since a read() call might return only part of a tab's expansion
to spaces, you'll need to keep track of how many spaces are "pending"
before consulting the InputStream (or Reader) again. There's a third
state variable.

     - Finally, you should give some thought to the skip() method.

     I hope this helps.  If you run into trouble, post what you've
managed to write and someone's sure to offer advice.

-- 
esosman@comcast-dot-net.invalid
"Don't be afraid of work. Make work afraid of you." -- TLM

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How to extend FilterInputStream to convert tabs to spaces? fangyuncn@gmail.com - 2015-03-08 06:47 -0700
  Re: How to extend FilterInputStream to convert tabs to spaces? Eric Sosman <esosman@comcast-dot-net.invalid> - 2015-03-08 11:33 -0400
    Re: How to extend FilterInputStream to convert tabs to spaces? Fang Yun <fangyuncn@gmail.com> - 2015-03-09 01:08 -0700
      Re: How to extend FilterInputStream to convert tabs to spaces? Arne Vajhøj <arne@vajhoej.dk> - 2015-04-18 21:10 -0400

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