Diff in Java

A workmate of mine is currently deep involved in a big deploy. He has to take a huge amount of sql scripts out of our SCM, check them manually to discover if the other programmers have followed the internal coding standard and fix them if this is not the case.

While it is still a mistery to me why nobody though to it, I started the development of a small tool that could possibly automatically check and fix all the errors.

Part of this tool is a diff style window that show the user what the tool is fixing. It seems that diff in Java is a quite required feature, so, here’s my solution.

Obviously I didn’t reinvented the weel and my implementation is 100% based on the one published on wikibooks. My implementation consist of a couple of class.
The first one is able to give access to strings line by line.

  1. public class LineFile {
  2.  
  3.  private List lines;
  4.  
  5.  public LineFile(InputStream in) {
  6.   try {
  7.    lines = IOUtils.readLines(in);
  8.   } catch (Exception e) {
  9.    throw new RuntimeException(e);
  10.   }
  11.  }
  12.  
  13.  public LineFile(File f) {
  14.   try{
  15.    lines = IOUtils.readLines(new FileInputStream(f));
  16.   }catch(Exception e){
  17.    throw new RuntimeException(e);
  18.   }
  19.  }
  20.  
  21.  public LineFile(String from) {
  22.   try {
  23.    lines = IOUtils.readLines(new ByteArrayInputStream(from.getBytes()));
  24.   } catch (IOException e) {
  25.    throw new RuntimeException(e);
  26.   }
  27.  }
  28.  
  29. public String lineAt(int index){
  30.  if(index>=0 && index<lines.size()){
  31.  return lines.get(index);
  32.  }
  33.  return null;
  34.  }
  35.  
  36.  public int lines() {
  37.  return lines!=null ? lines.size() : 0;
  38.  }
  39. }

The second one is the actual implementation of the diff algorithm, and is based on considering each line as the most little element the algorithm can consider.

  1. public class LineFile {
  2.  
  3.  private List<String> lines;
  4.  
  5.  public LineFile(InputStream in) {
  6.   try {
  7.    lines = IOUtils.readLines(in);
  8.   } catch (Exception e) {
  9.    throw new RuntimeException(e);
  10.   }  
  11.  }
  12.  
  13.  public LineFile(File f) {
  14.   try{
  15.    lines = IOUtils.readLines(new FileInputStream(f));  
  16.   }catch(Exception e){
  17.    throw new RuntimeException(e);
  18.   }
  19.  }
  20.  
  21.  public LineFile(String from) {
  22.   try {
  23.    lines = IOUtils.readLines(new ByteArrayInputStream(from.getBytes()));
  24.   } catch (IOException e) {
  25.    throw new RuntimeException(e);
  26.   }
  27.  }
  28.  
  29.  public String lineAt(int index){
  30.   if(index>=0 && index<lines.size()){
  31.    return lines.get(index);
  32.   }
  33.   return null;
  34.  }
  35.  
  36.  public int lines() {
  37.   return lines!=null ? lines.size() : 0;
  38.  }
  39. }

Finally, to give you an idea of how it performs, here’s a couple of screenshots from the application.

If you need more details regarding the code, don’t hesitate and drop me a message!