Can i read file in java and print its contents without comment statements?

Question

When i read java file as tokens and print it's content, using BufferedReader and StringTokenizer,how can i print only its content without comment statements that begin with " // " , " /* */" . I want to print content of file without these statement that used for clarify the code.

Answer 1

You can do that very easily using JavaParser: just parse the code specifying that you want to ignore comments and then dump the AST

CompilationUnit cu = JavaParser.parse(reader, false /*considerComments*/);
String codeWithoutComments = cu.toString();

While dumping it will reformat the code.

Answer 2

1 If you want to remove comments, you can well:

• remove // => see the same question here, no need of regex : Find single line comments in byte array

• remove /* */ it is more difficult. regex could work, but you could get a lot of pain . I dont recommend that

2 use a java parser : Java : parse java source code, extract methods

javaparser for example: https://github.com/javaparser/javaparser

then iterate the code, and remove comments, etc.

Answer 3

This code will remove the comment inside a text file.But, It will not remove the symbols of comment, if you need to remove it, you can do it by editing the three functions which I had written below.Test case which i had tested.

// helloworld
/* comment */
a  /* comment */
b
/*
comment
*/
c
d
e
// xxxx
f // xxxx

The Output will be:

//
/* */
a  /* */
b
/*

*/
c
d
e
//
f //

In this program I didn't remove the comment symbol as I was making lexical analyzer.You can remove the comment symbols by editing the program statements where i had put the comments.

public class testSpace {
public static void main(String[] args) {
    try {
        String filePath = "C:\\Users\\Sibil\\eclipse-workspace\\Assignment1\\src\\Input.txt";
        FileReader fr = new FileReader(filePath);
        String line;
        BufferedReader br = new BufferedReader(fr);
        int lineNumber = 0;
        while ((line = br.readLine()) != null) {
            lineNumber++;
            if ((line.contains("/*") && line.contains("*/")) || (line.contains("//"))) {
                line = findreplacement(line);
                System.out.println(line);//Begining of the multiline comment
            } else if (line.contains("/*")) {
                line = getStartString(line);
                System.out.println(line);
                while ((line = br.readLine()) != null) {
                    lineNumber++;
                    if (line.contains("*/")) {
                        line = getEndString(line);
                        System.out.println(line);//Print the end of a Multline comment
                        break;
                    } else {
                        line = " ";
                        System.out.println(line);//Blank Space for commented line inside a multiline comment 
                    }
                }
            } else
                System.out.println(line);//Line without comment
        }
    } catch (Exception e) {
        System.out.println(e);
    }
}

private static String getEndString(String s) {
    int end = s.indexOf("*/");
    String lineEnd = s.substring(end, s.length());//Edit here if you don't need the comment symbol by substracting 2 or adding 2
    return lineEnd;
}

private static String getStartString(String s) {
    int start = s.indexOf("/*");
    String lineStart = s.substring(0, start + 2);//Edit here if you don't need the comment symbol by substracting 2 or adding 2
    return lineStart;
}

private static String findreplacement(String s) {
    String line = "";
    if (s.contains("//")) {
        int start = s.indexOf("//");
        line = s.substring(0, start + 2);//Edit here if you don't need the comment symbol by substracting 2 or adding 2
    } else if ((s.contains("/*") && s.contains("*/"))) {
        int start = s.indexOf("/*");
        int end = s.indexOf("*/");
        String lineStart = s.substring(0, start + 2);//Edit here if you don't need the comment symbol by substracting 2 or adding 2
        String lineEnd = s.substring(end, s.length());//Edit here if you don't need the comment symbol by substracting 2 or adding 2
        line = lineStart + " " + lineEnd;
    }
    return line;
}
}

If your file has a line like this,

System.out.println("Hello World/*Do Something */");

It will fail and the output will be:

System.out.println("Hello world");