Input & Output in Java — Revision Notes

Definition

Syntax

import java.util.Scanner;
Scanner sc = new Scanner(System.in);
int x = sc.nextInt();
String s = sc.nextLine();

Example

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        System.out.print("Enter your age: ");
        int age = sc.nextInt();
        System.out.println("You are " + age + " years old.");
    }
}

Output

Important Points

• Scanner must be imported: import java.util.Scanner;.
• nextInt(), nextDouble(), and nextLine() read different types of input.
• Mixing nextInt() and nextLine() can cause a subtle bug where a leftover newline is read as empty input.
• System.out.print() doesn't add a newline; println() does.

Common Mistakes

• Forgetting to import java.util.Scanner.
• Calling nextLine() right after nextInt() without consuming the leftover newline first.
• Not closing the Scanner in larger programs (a resource-leak habit worth avoiding).

Interview Tip