Reading until the input ends

This module is about reading data from files. A program reads a file one line at a time, much as it reads what a user types, so it starts at the keyboard.

Module 19 read input in a while (true) loop that stops at a signal, such as an empty line: read a line, break if it's the signal, and only then use it. This step adds two more ways to know when to stop.

Until the input ends

A Scanner's hasNextLine() tells whether there's another line to read. It's true while there is one, and false once the input has ended, so a loop can read every line without waiting for a signal:

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int count = 0;
        while (scanner.hasNextLine()) {
            String line = scanner.nextLine();
            count++;
            System.out.println(count + ": " + line);
        }
        System.out.println("Lines: " + count);
    }
}

red
green
blue

1: red
2: green
3: blue
Lines: 3

• hasNextLine() only looks. nextLine() then reads the line, so the next round sees the line after it.
• An empty line is a line too: hasNextLine() is true for it, and nextLine() gives "".
• In the checks on this site, the input ends after its last line. A person at a keyboard has no natural end, which is why keyboard programs usually wait for a stop signal instead. (In a terminal, Ctrl+D ends the input, or Ctrl+Z and then Enter on Windows.)

A file does have an end, and this loop is exactly how the next steps read one.

A stop word in any capitals

A stop word typed by a person may come as end, End or END. equalsIgnoreCase from module 16 accepts all of them:

String line = scanner.nextLine();
if (line.equalsIgnoreCase("end")) {
    break;
}