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2008-11-03T05:21:04Z

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== A simple differencing tool ==

=== Prerequisites ===
* You need to know how to read from files using a java.io.Reader implementation - if you don't, do [[SE251Ex:File_Reverser]] first.
* Also, it would help a lot if you have already completed [[SE251Ex:Set_Operations]] and [[SE251Ex:Chain]].

=== Description ===
Write a simple differencing tool that takes in two files, A and B, and outputs all lines in A that B doesn't contain and conversely all lines in B that A doesn't contain. For example, say file ''A.txt'' contains the following lines:
<pre>
Hello there.
You're reading file A.
Nice hair,
Aye Aye.
Hello there.
Good bye.
</pre>
And file ''B.txt'' contains the following lines:
<pre>
Hello there.
You're reading file B.
Nice hair,
Hello hello.
Good bye.
</pre>

Then the output of the program will be something like:
<pre>
-- Lines unique to A.txt:
You're reading file A.
Aye Aye.
-- Lines unique to B.txt:
You're reading file B.
Hello hello.
</pre>

Note that lines are considered equivalent if they contain exactly the same sequence of characters - e.g. although there are two occurrences of "Hello there." in A.txt they are essentially considered as one.

Exactly how the user specifies the file names is up to you: you can do it either by prompting through the console, or through command line arguments.

=== Tips ===
Realise this is effectively a set difference problem. The basic idea is to convert the lines from both files into the respective sets and compute the difference.

=== Optional requirements ===
Optionally, ensure that the order in which the unique lines are presented is consistent with the order in which they appear in the original file. In other words, below shouldn't happen because the line "You're reading file A" comes before "Aye Aye." inside A.txt; likewise "You're reading fileB" comes before "Hello hello" inside B.txt:
<pre>
-- Lines unique to A.txt:
Aye Aye.
You're reading file A.
-- Lines unique to B.txt:
Hello hello.
You're reading file B.
</pre>
To do this you may want to utilise the ''Chain'' data structure from [[SE251Ex:Chain]], which is in one way a special kind of Set that retains the ordering in which elements were added.

== Discussion ==
Here you can ask questions and discuss stuff

SE251Ex:Differencing - Revision history

Mark: 7 revision(s)