File Merging --- Need Help

Question

Greetings,
I am pretty new at this program, and I am trying to understand how to do my homework assignment. So I do not need the full code, just some help on how to get started.
I am trying to write a program that merges all files together whose names match a certain pattern, and writes the result to an output file. The input-file pattern will consist of a combination of "normal" filename characters and question marks (?). A question mark in the input-file pattern denotes a single-character "wild card". Thus, the pattern ab?c?.txt would denote all file names that consist of 9 characters such that:
the first two characters are ab
the fourth character is c
the last four characters are .txt
For example, this would include filenames such as abxc7.txt and abqcc.txt.
So if there are files in a folder, for example, called abc.txt, adc.txt, cat.txt, and the contents of each has two similar lines of "This is File ZZZ" Where ZZZ represents the name of the file. Then running the program with the pattern a??.txt and the output file finished.txt will result in the file finished.txt having the contents
This is file abc.txt.
This is file abc.txt.
This is file abd.txt.
This is file abd.txt.
I don't really know where to begin here. Could you help me out? Thanks

Answer 1

Check out the API docs for java.io.File. It has methods to list all the files in a particular directory.
For the name matching, you can create a class that implements FileFilter or FileNameFilter that you then pass to these methods.
The filter's accept method would test the file name against your criteria.
(You wouldn't have to use the filter. You could just iterate over the files and compare each one yourself.)
To do the actual comparison, you could use the String.matches() method or you could just do the character by character comparison yourself.
If you google for java io tutorial you should find something that will help you with the File class, and java regex tutorial for String.match()
Break the problem into small pieces, and get each one working before moving onto the next.
First write a method that takes in a pattern "a?bc?.txt" and a String (that represents a filename) and returns true or false depending on whether it mathes.
Then write a method that takes the patten and an array or List of Strings or Files and uses the first method to return an array or List of Strings or Files that represents the subset of the original list that matched.
Post again if you have specific questions about specific parts that you don't understand or cant' get to work.