Reading input with Scanner

Key points

• new Scanner(System.in) reads the console. A Scanner over a String runs the same code in a test.
• nextLine() takes the rest of the line, while next() and nextInt() take one token.
• Check before you read: hasNextInt() avoids the InputMismatchException a stray word would cause.
• nextInt() leaves the newline behind, so the next nextLine() comes back empty. Read lines and parse them.
• Reading past the end throws NoSuchElementException, so drive the loop with hasNext().
• Close it with try-with-resources — but never close a Scanner over System.in while you still need input.

Example

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        // A real program uses new Scanner(System.in). A String source keeps this demo repeatable.
        String typed = "Ada\n36\nred green blue\n";

        try (Scanner in = new Scanner(typed)) {
            String name = in.nextLine();
            int age = Integer.parseInt(in.nextLine());
            System.out.println(name + " is " + age + " years old");

            String[] colours = in.nextLine().split(" ");
            System.out.println("read " + colours.length + " colours, first = " + colours[0]);
        }

        try (Scanner tokens = new Scanner("10 20 hello 30")) {
            int total = 0;
            while (tokens.hasNext()) {
                if (tokens.hasNextInt()) {
                    total += tokens.nextInt();
                } else {
                    System.out.println("not a number, skipping: " + tokens.next());
                }
            }
            System.out.println("total of the numbers: " + total);
        }

        System.out.println("nextInt() leaves the newline behind - that is why a later nextLine() looks empty");
    }
}

Guard every read with hasNextX, and prefer nextLine plus parse.