Question

I would like to perform checking on the following:

VALID LINES;
/**/ some code
*/ some code   /** dsfsdkf sd**/

NOT VALID LINES;
/**/ //some code
*/ /***/ //somecode

So basically if there is a line of code outside a comment it is valid, otherwise not.

What would be the best way to tackle this kind of validation?

Note:
For */ I assume that the /* has been opened some lines before.

Answer 1

This should be quite fast I believe.

import java.io.*;

class Test {

    public static void main(String[] args) throws IOException {
        StringBuffer buf = new StringBuffer();
        BufferedReader r = new BufferedReader(new FileReader("src/Test.java"));

        final String nl = System.getProperty("line.separator");
        String line;
        while (null != (line = r.readLine()))
            buf.append(line).append(nl);

        for (String code : buf.toString().split("(?ms)/\\*.*?\\*/|//[^\\n]*"))
            System.out.println(code);
    }
}

If you read up a bit on the internals of reg-exps you’ll realize that regular expressions are quite efficient once the underlying automaton has been compiled and minimized (at least for simple regular expressions like the one above). No matter how you implement your algorithm, it would still need to do roughly the same work that the reg-exp engine does in this scenario anyway.

(If you look at the String.split method, you’ll note that the internal regular expression is compiled into a Pattern once and for all.)