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I am working with file reader and writer using text files. Basically implementing a dfa of pascal grammer that will handle comments in a program. For this I have used 3 text files 1 file to read data from, 1 to write token in it and 1 to write error token in it. The pascal compiler does not consider this {{ as a comment because the comment syntax is "{this is a comment}" . I used an array of [5][4] for this purpose and I used file reader to read from a text file name "code.txt" containing this text "{a}". But the problem is that when i write this into a new text file name "token.txt" (initially writing it in token.txt but it should be in error.tx), it prints this {{a} means that it prints the first character two times like {{ . I want to output same as I have written it in the code.txt file. Thanks in advance.

public class Lex {


    public static char dfa1[][] = new char[5][4];



        /*
         * for(int i=0; i<5; i++) { for(int j=0; j<4; j++) {
         * System.out.println("arr["+i+"]["+j+"]"+dfa1[i][j]); } }
         */
        //FileReader fr = new FileReader(filename);
        //BufferedReader br = new BufferedReader(fr);

        File file = new File("code.txt");
        BufferedReader reader = null;
        int StartState = 1;
        char CurrentState = '1';
        int acp =0;
        String temptok = new String();
        try {
            reader = new BufferedReader(new FileReader(file));
            int i;

            // repeat until EOF
            while ((i = reader.read()) != -1) {
                char c = (char) i;
                if (c == '{') {
                    if (CurrentState == dfa1[1][0]) {
                        CurrentState = '2';
                        acp =0;
                        temptok = temptok.concat(String.valueOf(c));
                    } else if (CurrentState == dfa1[2][0]) {
                        temptok = temptok.concat(String.valueOf(c));
                        acp =0;
                        CurrentState = '4';
                    } else if (CurrentState == dfa1[3][0]) {
                        temptok = temptok.concat(String.valueOf(c));
                        CurrentState = '4';
                        acp =0;
                    } else if (CurrentState == dfa1[4][0]) {
                        temptok = temptok.concat(String.valueOf(c));
                        acp =0;
                        break;
                    }
                }
                if (c == '}') {
                    if (CurrentState == dfa1[1][0]) {
                        acp =0;
                        temptok = temptok.concat(String.valueOf(c));
                        break;
                    } else if (CurrentState == dfa1[2][0]) {
                        temptok = temptok.concat(String.valueOf(c));
                        CurrentState = '3';
                        acp = 1;
                    } else if (CurrentState == dfa1[3][0]) {
                        temptok = temptok.concat(String.valueOf(c));
                        CurrentState = '3';
                        acp = 1;
                    } else if (CurrentState == dfa1[4][0]) {
                        temptok = temptok.concat(String.valueOf(c));
                        acp = 0;
                        break;
                    }
                }
                if (c != '}') {
                    if (CurrentState == dfa1[1][0]) {
                        temptok = temptok.concat(String.valueOf(c));
                        acp =0;
                        break;
                    } else if (CurrentState == dfa1[2][0]) {
                        temptok = temptok.concat(String.valueOf(c));
                        CurrentState = '2';
                        acp =0;
                    } else if (CurrentState == dfa1[3][0]) {
                        temptok = temptok.concat(String.valueOf(c));
                        acp =0;
                        break;
                    } else if (CurrentState == dfa1[4][0]) {
                        temptok = temptok.concat(String.valueOf(c));
                        acp =0;
                        break;
                    }
                }


                //System.out.println(temptok);

                PrintWriter writer = new PrintWriter("token.txt", "UTF-8");
                PrintWriter ewriter = new PrintWriter("error.txt", "UTF-8");
                if(acp == 1){
                writer.println(temptok);
                writer.close();
                }
                else if(acp == 0)
                {
                    ewriter.println(temptok);
                ewriter.close();
                }
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2 Answers 2

Reset to default
2

You have a chain of if blocks, and not a chain of if, else if, else if blocks. So, when { is read, those two conditions are true, and the char is written twice:

if (c == '{') {
    ...
}
...
if (c != '}') {
    ...
}

Also, you shouldn't use String.concat(), but you should use a StringBuilder instead. And you should respect Java naming conventions: variables start with a lower-case letter. Also consider improving your naming: dfa1 and acp aren't descriptive names. temptok and ewriter should be named temporaryToken and errorWriter.

Final note: this is the kind of problems that are diagnosed immediately when you step through the code using a debugger. Learn using the debugger: it will save you hours of debugging time.

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2 Comments

i was just posting the same as you :)
@JB Nizet Thank you very much, your answer was really helpful for me.
0

Your third if:

if (c != '}')

seems like that should be:

if (c != '}' && c != '{')

Also, this doesn't seem like the most optimal way to process the file.

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