java.util.NoSuchElementException: No line found*

Question

I keep getting this error java.util.NoSuchElementException No line found when I use this method

public boolean hasMoreCommands() {
    if (input.hasNextLine()) {
        return true;
    } else {
        //input.close();
        return false;
    }
}

public void advance() {
    String str;
    if(hasMoreCommands() == true){
        do {
            str = input.nextLine().trim();

            // Strip out any comments
            if (str.contains("//")) {
                str = (str.substring(0, str.indexOf("//"))).trim();
            }
        } while (str.startsWith("//") || str.isEmpty() || hasMoreCommands());
        command = str;
  }
}

I have main code here:

public class Ptest
{
  public Ptest(String fileName)
  {
    String line = null;
    String nName = fileName.replace(".vm", ".asm");
    Parser p = new Parser();

    try{ 
        File neF = new File(nName);
        if(!neF.exists()){
            neF.createNewFile();
        }
        File tempFile = new File("temp.txt");
        if(!tempFile.exists()){
            tempFile.createNewFile();
        }

        FileReader fr = new FileReader(fileName);
        BufferedReader br = new BufferedReader(fr);
        FileWriter fw = new FileWriter(nName);
        BufferedWriter bw = new BufferedWriter(fw);
        FileWriter writR = new FileWriter(tempFile);
        BufferedWriter buffR = new BufferedWriter(writR);
        while((line = br.readLine()) != null) {
            buffR.write(line+ "\n");
            //System.out.println(line);
        }  
        buffR.flush();
        buffR.close();
        p.insertTitle(tempFile);
        String ctype = p.commandType();
        int len = ctype.length();
        int spaces = 13 - len;
        String sp = " ";
        String asp = " ";
        String a1 = null;
        int a2;
        int alen;
        boolean t = false;
        while(p.hasMoreCommands()){
            for(int i= 0; i < spaces; i++){
                sp += " ";
            }
            t = p.hasMoreCommands();
            a1 = p.arg1();
            alen = (10 - a1.length());
            for(int i= 0; i < alen; i++){
                asp += " ";
            }
            //a2 = p.arg2();
            if (ctype == "C_PUSH" || ctype == "C_POP" || ctype == "C_FUNCTION" || ctype == "C_CALL") {
                a2 = p.arg2(); 
                bw.write(ctype + sp + a1 + asp + a2);
            }
            else {
                bw.write(ctype + sp + a1);
            }
            p.advance();
            ctype = p.commandType();
            len = ctype.length();
            spaces = 13 - len;
        }

        bw.flush();
        bw.close();
    }
    catch(FileNotFoundException ex){
        System.out.println("File not found!");
    }
    catch(IOException ex){
        System.out.println("Error reading file '"  + fileName + "'");
    }
  }
}

I went through debugger and it literally goes the entire file then gives me an error when its finished.

Answer 1

Like @hfontanez I think your problem is in this code:

if(hasMoreCommands() == true){
    do {
        str = input.nextLine().trim();

        // Strip out any comments
        if (str.contains("//")) {
            str = (str.substring(0, str.indexOf("//"))).trim();
        }
    } while (str.startsWith("//") || str.isEmpty() || hasMoreCommands());
    command = str;
}

However, my solution is to change the while clause to while (str.isEmpty() && hasMoreCommands());

I'm assuming that "advance" ought to return the next non-comment / blank line.

If the string from the previous pass is empty (after stripping any comment) it will go round the loop again provided that wasn't the last line. But, if that was the last line or str still has something in it, then it will exit the loop. Comments should have been stripped so don't need tested for in the while.

I think if you just test for hasNextLine within the loop then it will never exit the loop if the last line was comment / blank.

Answer 2

My guess is that your problem is here:

if(hasMoreCommands() == true){
    do {
        str = input.nextLine().trim();

        // Strip out any comments
        if (str.contains("//")) {
            str = (str.substring(0, str.indexOf("//"))).trim();
        }
    } while (str.startsWith("//") || str.isEmpty() || hasMoreCommands());
    command = str;
}

The exception you encountered (NoSuchElementException) typically occurs when someone tries to iterate though something (String tokens, a map, etc) without checking first if there are any more elements to get. The first time the code above is executed, it checks to see if it has more commands, THEN it gets in a loop. The first time it should work fine, however, if the test done by the while() succeeds, the next iteration will blow up when it tries to do input.nextLine(). You have to check is there is a next line to be got before calling this method. Surround this line with an if(input.hasNextLine()) and I think you should be fine.