Question

I am trying to create a program which will read a file and check whether the text is a palindrome or not. The code compiles, but doesnt really work.

The problem is I dont know how to break a complete token into characters or assign it to a string in order to use string’s length to push(enqueue) each letter or digit into the stack(queue). Can anyone suggest a solution for this?

public static void main(String [] args) throws IOException{
    StackReferenceBased stack = new StackReferenceBased();
    QueueReferenceBased queue = new QueueReferenceBased();
    Scanner s = null;
    String fileName=args[0]+".txt";
    int symbols = 0;
    int lettersAndDigits =0;
    int matches = 0;

    try{
      s = new Scanner(new File(fileName));
      while(s.hasNext()){
        String current = s.next();
        for(int i=0;i<current.length();i++){
          char temp = s.next().charAt(i);
          if(Character.isLetterOrDigit(temp)){
            stack.push(temp);
            queue.enqueue(temp);
            lettersAndDigits++;

          }
          else {
            symbols++;

          }
        }
      }
      System.out.println("There are: " + " "+ symbols + " " +"symbols and " + " "+lettersAndDigits + " "+ "digits/letters");


    }
    catch (FileNotFoundException e) {
      System.out.println("Could not open the file:" + args[0]);
    } //catch (Exception e) {
      //System.out.println("ERROR copying file");
      finally {
      if(s != null){
        s.close();
      }
    }
    while (!stack.isEmpty()){
      if(!stack.pop().equals(queue.dequeue())){
          System.out.println("not pali");
          break;
        }
      else {
        ++matches;
      }
    }

    if(matches==lettersAndDigits){
      System.out.print("pali");
    }  
  }

Answer 1

Instead of

char temp = s.next().charAt(i); 

you need

char temp = current.charAt(i); 

By calling s.next() you read the next token from the file and try to access the ith element of that token based on the first string’s (current) length, which will lead to exceptions if the tokens read are shorter than the first stoken