5.11 Reading User Input

This lesson builds a small Java program that reads input from the keyboard. The class we use is Scanner from java.util.Scanner. We instantiate it with Scanner scanner = new Scanner(System.in);: new creates a fresh instance and System.in is the standard input stream.

We then prompt the user with System.out.println("Enter your name:"); and capture the reply with String name = scanner.nextLine();. The method nextLine() blocks until the user types something and presses Enter; the typed string is then assigned to the name variable. Printing "Your name is " + name echoes it back.

Reading an int and computing an age

• Prompt with "Enter your birth year:".
• Read an integer with int birthYear = scanner.nextInt();.
• Compute the age with int age = 2021 - birthYear; and concatenate the message "You are " + age + " years old".
• End with scanner.close(); to release the underlying stream.

One subtle detail: after nextInt() the cursor stays on the same line, so a follow-up nextLine() reads an empty string. Calling an extra scanner.nextLine(); after nextInt() consumes that leftover newline. With these few lines you have a Java program that talks to its user instead of staying silent.