Filter Streams in Java

[dmjpro]

I checked out the Source code of Filter Streams in Java.
There i saw there is a corresponding underlying Streams and the methods simply being used of underlying Streams'.
One thing is mentioned chaining is there ... can you explain how it's significant?

[r035198x]

Which classes exactly were you looking at and where is the chaining mentioned?

[dmjpro]

I am talking about the both Filter Streams (Input and Output). And have a look at this link for chaining ;)

[r035198x]

So I don't get your question. Chaining (and its benefits) are already explained on that site.

[dmjpro]

Well.... Then how chaining works? And there is no difference between InputStream and FilterInputStream? Then why the filtering comes in?

[JosAH]

@dmjpro
As per the API documentation: the FilterXXXStream classes wrap another XXXStream and do nothing by themselves, i.e. you have to sub-class those classes to make them do anything useful. e.g. the following class doesn't print any vowels:

public class ConsonantStream extends FilterOutputStream {
 
   public ConsonantStream(OutputStream os) { super(os); }
 
   public void write(int  b) throws IOException {
      if ("aeiouAEIOU".indexOf((char)b) == -1)
         super.write(b);
   }
}
 

According to the documentation all the other write methods use this single argument method so everything ends up at that method for the actual writing.

kind regards,

Jos

[dmjpro]

Well, so add extra functionality i have to make my own ;)
Now what about chaining? How does it come into these streams ?

[JosAH]

@dmjpro
The FileOutputStream's methods all call its write(int b) method which, in turn calls the same method from the encapsulate OutputStream. That is what chaining is all about. You wrote you have read the source code of those filter streams, so you should've read how those classes implement it. Also re-read my little example: it is chained between a target OutputStream and the caller of my stream. That entire process can be repeated at will but chaining doesn't "come into streams"; it is just the decorator/wrapper pattern that does it all.

kind regards,

Jos