Removing all types of comments in java file

Question

I have a java project and i have used comments in many location in various java files in the project. Now i need to remove all type of comments : single line , multiple line comments . Please provide automation for removing comments. using tools or in eclipse etc.

Currently i am manually trying to remove all commetns

Answer 1

You can remove all single- or multi-line block comments (but not line comments with //) by searching for the following regular expression in your project(s)/file(s) and replacing by $1:

^([^"\r\n]*?(?:(?<=')"[^"\r\n]*?|(?<!')"[^"\r\n]*?"[^"\r\n]*?)*?)(?<!/)/\*[^\*]*(?:\*+[^/][^\*]*)*?\*+/

It's possible that you have to execute it more than once.

This regular expression avoids the following pitfalls:

1. Code between two comments /* Comment 1 */ foo(); /* Comment 2 */

2. Line comments starting with an asterisk: //***NOTE***

3. Comment delimiters inside string literals: stringbuilder.append("/*");; also if there is a double quote inside single quotes before the comment

To remove all single-line comments, search for the following regular expression in your project(s)/file(s) and replace by $1:

^([^"\r\n]*?(?:(?<=')"[^"\r\n]*?|(?<!')"[^"\r\n]*?"[^"\r\n]*?)*?)\s*//[^\r\n]*

This regular expression also avoids comment delimiters inside double quotes, but does NOT check for multi-line comments, so /* // */ will be incorrectly removed.

Answer 2

I had to write somehting to do this a few weeks ago. This should handle all comments, nested or otherwise. It is long, but I haven't seen a regex version that handled nested comments properly. I didn't have to preserve javadoc, but I presume you do, so I added some code that I belive should handle that. I also added code to support the \r\n and \r line separators. The new code is marked as such.

public static String removeComments(String code) {
    StringBuilder newCode = new StringBuilder();
    try (StringReader sr = new StringReader(code)) {
        boolean inBlockComment = false;
        boolean inLineComment = false;
        boolean out = true;

        int prev = sr.read();
        int cur;
        for(cur = sr.read(); cur != -1; cur = sr.read()) {
            if(inBlockComment) {
                if (prev == '*' && cur == '/') {
                    inBlockComment = false;
                    out = false;
                }
            } else if (inLineComment) {
                if (cur == '\r') { // start untested block
                    sr.mark(1);
                    int next = sr.read();
                    if (next != '\n') {
                        sr.reset();
                    }
                    inLineComment = false;
                    out = false; // end untested block
                } else if (cur == '\n') {
                    inLineComment = false;
                    out = false;
                }
            } else {
                if (prev == '/' && cur == '*') {
                    sr.mark(1); // start untested block
                    int next = sr.read();
                    if (next != '*') {
                        inBlockComment = true; // tested line (without rest of block)
                    }
                    sr.reset(); // end untested block
                } else if (prev == '/' && cur == '/') {
                    inLineComment = true;
                } else if (out){
                    newCode.append((char)prev);
                } else {
                    out = true;
                }
            }
            prev = cur;
        }
        if (prev != -1 && out && !inLineComment) {
            newCode.append((char)prev);
        }
    } catch (IOException e) {
        e.printStackTrace();
    }

    return newCode.toString();
}