Question

How do I read multiple lines (in Java) from an input file (say, helloworld.in)?

The input file does not have a fixed number of lines, it can have anywhere from 3 to 99999 lines.

Answer 1

Use a java.util.Scanner:

Scanner scanner = new Scanner(new File("helloworld.in"));
while (scanner.hasNext()) {
    String line = scanner.nextLine();
    // Do something
}

With a scanner, you can also read specific types, eg scanner.nextInt() etc