Keyboard Input Using Scanner

1. Introduction

Taking input from the user is a common requirement in most Java applications.
Java provides several ways to read keyboard input, and the Scanner class is the most beginner-friendly and widely used method.

Scanner belongs to the java.util package and allows reading:

• Integers
• Floating values
• Strings
• Characters
• Boolean values

By the end of this lesson, you will know how to use Scanner effectively with all input types.

2. Importing Scanner

Before using Scanner, you must import it:

import java.util.Scanner;

This tells Java you want to use the Scanner class available in the standard library.

3. Creating a Scanner Object

To read input from the keyboard, create a Scanner object using System.in.

Scanner sc = new Scanner(System.in);

Here,

• sc → scanner reference
• new Scanner(System.in) → reads input from keyboard

This scanner object will now be used to read different types of data.

4. Reading Different Types of Input

Scanner provides several methods to read user input.

4.1 Reading an Integer

int age = sc.nextInt();

Example:

System.out.print("Enter your age: ");
int age = sc.nextInt();
System.out.println("Your age is: " + age);

4.2 Reading a Double

double price = sc.nextDouble();

4.3 Reading a Boolean

boolean isActive = sc.nextBoolean();

4.4 Reading a Single Word (String)

To read a single word (without spaces):

String name = sc.next();

Example:

System.out.print("Enter your name: ");
String name = sc.next();
System.out.println("Hello, " + name);

4.5 Reading a Full Line

To read a full line including spaces:

String sentence = sc.nextLine();

Example:

System.out.print("Enter a sentence: ");
String sentence = sc.nextLine();
System.out.println("You entered: " + sentence);

5. Important Note: nextLine() Issue After nextInt()

When you use nextInt(), nextDouble(), etc., they do not read the newline character (\n). This creates a common beginner problem where nextLine() gets skipped.

Example of problem:

int age = sc.nextInt();
String name = sc.nextLine(); // gets skipped!

Fix

Call an extra nextLine() to consume the leftover newline.

int age = sc.nextInt();
sc.nextLine(); // consume newline
String name = sc.nextLine();

6. Closing the Scanner

Scanner uses system resources, so you should close it.

sc.close();

Do NOT close Scanner if used inside large applications where System.in is needed later.

7. Full Example Program

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();
        sc.nextLine(); // fix for nextLine()

        System.out.print("Enter your full name: ");
        String name = sc.nextLine();

        System.out.print("Enter your salary: ");
        double salary = sc.nextDouble();

        System.out.println("\n--- Output ---");
        System.out.println("Name: " + name);
        System.out.println("Age: " + age);
        System.out.println("Salary: " + salary);

        sc.close();
    }
}

8. Summary

• Scanner is a simple and powerful class for reading keyboard input.
• Use nextInt(), nextDouble(), next(), and nextLine() for different input types.
• Remember the nextLine() issue after numeric inputs.
• Always close the Scanner when done (unless System.in is required later).

Written By: Shiva Srivastava