Opening a file

Create a File with the file's name and pass it to a Scanner. Because the file might not exist, the method must say what happens then; the simplest way is throws IOException in the header. File and IOException are in java.io; Scanner is in java.util.

import java.io.*;
import java.util.*;

public static void main(String[] args) throws IOException {
  Scanner sc = new Scanner(new File("scores.txt"));
  // ... read ...
  sc.close();
}

Reading tokens

Suppose scores.txt holds a name and a score on each line. next() reads one word and nextInt() reads one integer, skipping spaces and line breaks.

Scanner sc = new Scanner(new File("scores.txt"));
int total = 0;
while (sc.hasNext()) {
  String name = sc.next();
  int score = sc.nextInt();
  total += score;
  System.out.println(name + ": " + score);
}
sc.close();
System.out.println("total " + total);

Ava: 91
Ben: 78
Cy: 85
total 254

Reading lines and splitting

For comma-separated data, read whole lines with nextLine() and break each into fields with split(","). Convert number fields with Integer.parseInt.

Scanner sc = new Scanner(new File("cities.txt"));
String biggest = "";
int most = 0;
while (sc.hasNext()) {
  String[] f = sc.nextLine().split(",");
  int pop = Integer.parseInt(f[2]);
  if (pop > most) {
    most = pop;
    biggest = f[0];
  }
}
sc.close();
System.out.println(biggest);

Austin

Scanner methods (on the Quick Reference)