如何跳过用扫描仪读取一行

Question

I have read in a text file and am scanning said file. The question I have is how would I skip over lines that include a certain character (in my case lines that start with " // " and " " (whitespace).

Here is my code at the moment. Can someone point me in the right direction?

    File dataFile = new File(filename);
    Scanner scanner = new Scanner(dataFile);


      while(scanner.hasNext())
      {
         String lineOfText = scanner.nextLine();
         if (lineOfText.startsWith("//")) {
           System.out.println(); // not sure what to put here
         }
      System.out.println(lineOfText);
      }
   scanner.close();

Answer 1

You will only want to execute the code within the while-loop if the line of text doesn't start with a / or whitespace. You can filter these out as seen below:

while(scanner.hasNext()) {
   String lineOfText = scanner.nextLine();
   if (lineOfText.startsWith("//") || lineOfText.startsWith(" ")) {
      continue; //Exit this iteration if line starts with space or /
   }
   System.out.println(lineOfText);
}

Answer 2

As you are iterating over the lines of text in the file, use String 's startsWith() method to check if the line starts with the sequences you are trying to avoid.

If it does, continue to the next line. Otherwise, print it.

while (scanner.hasNext()) {
    String lineOfText = scanner.nextLine();

    if (lineOfText.startsWith("//") || lineOfText.startsWith(" ") ) {
        continue;
    }

    System.out.println(lineOfText);
}

Answer 3

Just use a continue like -

if (lineOfText.startsWith("//")) {
  continue; //would skip the loop to next iteration from here
}

Detials - What is the "continue" keyword and how does it work in Java?

Answer 4

If you're just interested in printing out the lines of code that begin with a "//" then you should just use the continue keyword in java.

String lineOfText = scanner.nextLine();
if (lineOfText.startsWith("//")) {
    continue;
}

See this post for more information regarding the "continue" keyword.

Answer 5

You can just insert "else" in your code like:

public static void main(String[] args) throws FileNotFoundException {

     File dataFile = new File("testfile.txt");
        Scanner scanner = new Scanner(dataFile);


          while(scanner.hasNext())
          {
             String lineOfText = scanner.nextLine();
             if (lineOfText.startsWith("//")) {
               System.out.println(); 
             }
             else
                 System.out.println(lineOfText);
          }
       scanner.close();
}

}