Data in a fixed format

Programs often read data in which every line has the same shape: a name and a score, or a city and a temperature. The values are separated by a character that doesn't appear in the values themselves, often a comma or a semicolon:

Mira,87
Otto,92

Each line is split at the separator, and the parts are picked out by their index. The parts are Strings, so a number has to be turned into an int with Integer.valueOf (or into a double with Double.valueOf) before you can calculate with it:

String line = "Mira,87";
String[] parts = line.split(",");
String name = parts[0];
int score = Integer.valueOf(parts[1]);
System.out.println(name + " scored " + score);
System.out.println("With the bonus: " + (score + 5));

Mira scored 87
With the bonus: 92

Without Integer.valueOf, parts[1] + 5 would join the two as text and give 875.

Decimal numbers separated by semicolons work the same way:

String line = "Oulu;-4.5";
String[] parts = line.split(";");
double temperature = Double.valueOf(parts[1]);
if (temperature < 0) {
    System.out.println(parts[0] + " is below freezing");
}

Oulu is below freezing

A space too many

Data typed by people isn't always tidy. If a line has a space after the comma, the second part starts with that space, and Integer.valueOf refuses it:

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        String line = scanner.nextLine();
        String[] parts = line.split(",");
        int score = Integer.valueOf(parts[1]);
        System.out.println(parts[0] + ": " + score);
    }
}

Mira, 87

Exception in thread "main" java.lang.NumberFormatException: For input string: " 87"
	at Main.main(Main.java:8)

The quotes in the message show the culprit: the text was " 87", with a space in front. trim() removes it, so Integer.valueOf(parts[1].trim()) works whether the space is there or not.

A line with no comma at all splits into just one part, and parts[1] then crashes with an ArrayIndexOutOfBoundsException. When the input might have lines like that, check parts.length before you use the parts.