A regex for a class definition in java

Question

The problem is as follows:

There is a massive codebase in Java (hundreds of files in tens of packages) where we need the ability to add and remove the keyword strictfp in each class definition. I am planning to use either sed or awk to perform this substitution. However, I would like to avoid the word "class" in comments or elsewhere from being replaced. Can anyone think of a solution for this?

Answer 1

How standard is the formatting of your code? For instance, could you look for 'class' in a line that ends with { or where the next line begins with { or some such?

Answer 2

No way to be certain to get this 100% right without a java parser. But, the following may be close enough:

sed -i.bak 's/\\(public\\|private\\|protected\\)\\(.*\\)class/\\1 strictfp \\2 class/g' $file

I think I got the escapes right, but I'm writing this from a windows machine and haven't tested it.

The above will trip up if you have comments with 'public/private/protected' followed by 'class'.

Answer 3

As a complete catch-all, no, there's no RegEx for that. You'd essentially need to write a Java interpreter (or at least a parser) in order to account for any theoretical construction of a class. That being said, you really should be safe if the word class is the first non-whitespace bit on the line, or if it's preceded by an access modifier that is the first non-whitespace bit on the line.

Answer 4

I can think of two possibilities:

• Use a parser rather than a regular expression (REs aren't meant for everything). A parser will far better understand the language syntax.
• Make your code base consistent so that you will not pick up errant "class" strings.

Neither of these are very satisfactory. The first is actually quite hard to write, the second hard to get right.

My advice would be to just find an RE and turn it loose on a local copy of the source code, then examine all the changes. Whatever changes that were made in error, tweak the RE and try again.

Then introduce coding standards and gradually change all the non-conforming definitions to be correct.

Answer 5

For such a task, I would first recommend writing a small program that verifies all the *.class files in a directory tree actually have (or do not have) the correct strictfp setting. Then, whatever you choose to do to solve the source code modification problem, you can run the checker after the compiler to make sure that you've done the right thing.

This is actually just TDD applied to your particular problem.

Answer 6

Since you want to switch back and forth between strictfp and no strictfp, it may be a better idea to modify the .class files as part of the build process. Then you can make this choice a build option and switch it without constantly changing source files.

Answer 7

Starblue: Thanks! From looking up BCEL, I found JMangler, which is perfect, since I can modify existing .class files to add the strictfp modifier. http://javalab.cs.uni-bonn.de/research/jmangler/tutorial/using.html

Answer 8

Just to let people know, I decided to go with Javassist in the end instead of BCEL, since Javassist seems to be a lot simpler to use and is perfectly adequate for my purposes. http://csg.is.titech.ac.jp/~chiba/javassist . In case anyone is curious, the code would go something like this:

    import javassist.*;
    ClassPool cp = new ClassPool(); 
    CtClass someClass = cp.get("SomeClass"); 
    someClass.setModifiers(Modifier.STRICT);