java using append to extract data from a line of a file

Question

I am extremely new to Java, as you can tell from my code. Any help is welcome :)

I have a file contains lines like:

Columns in File: 7

Exact File Quantity (Rows): 118

Exact File Record Length (Bytes in Variable Block): 52

I want to use append to extract the numbers after the label, but it returns zero, not the actual number after the label. Here is what I have:

   public int extractVariables(String aLine)
   {
    Scanner scan = new Scanner(actualFile);
    while(scan.hasNext())
    {
        String line = scan.nextLine();
        if(line.contains("Columns in File:"))
        {
            StringBuilder numOfVariables = new StringBuilder();
            for(int i = 16; i < line.length(); i++)
            {
                numOfVariables.append(charAt(i)).trim();
            }
      // check if the information is missing
                if(numOfVariables != null && !numOfVariables.equals(""))
                {
                    int variables = Integer.parseInt(numOfVariables);
                }
                else
                {
                    System.out.print("Number of varibales is missing!");
                }
            }
            return variables;
        }
    }

Also, I ask the user to input a file using command line argument, and store the file into actualFile, like this:

      try{
          File actualFile = new File(args[0]);
          System.out.println("File was processed: true");
         }
      catch (ArrayIndexOutOfBoundsException e)
        {
            System.out.println("File was processed: false. Re-enter filename.");
            return;
        }

So I put actualFile for the scanner to open the file and reads the lines, does the scanner reads the correct file? Maybe that's why the method returns zero?

Answer 1

Instead of doing

for(int i = 16; i < line.length(); i++)
        {
            numOfVariables.append(charAt(i)).trim();
        }

It seems better to make use of nextInt(); So, the code would look something like this:

line.nextInt();

Also, to check if there is a number or if it is missing, you can use:

if(line.hasNextInt()) {...}