Lesson 2.6: Taking User Input Using Scanner

Introduction

So far, all the programs we have written used hardcoded values. This means the values were already written inside the program.

However, real-world applications allow users to enter their own data. For example:

• A calculator asks users to enter two numbers.

• An ATM asks users to enter their PIN.

• A student management system asks users to enter their name, roll number, and marks.

To make Java programs interactive, Java provides the Scanner class, which allows us to take input from the keyboard.

In this lesson, you will learn how to use the Scanner class to accept different types of user input.

Learning Objectives

After completing this lesson, you will be able to:

• Understand the purpose of the Scanner class.

• Import the Scanner class.

• Create a Scanner object.

• Take different types of user input.

• Read integers, decimals, characters, and strings.

• Build simple interactive Java programs.

What is the Scanner Class?

The Scanner class is a predefined class in the java.util package.

It is used to read input from various sources such as:

• Keyboard

• Files

• Strings

In this course, we will use the Scanner class to take input from the keyboard.

Importing the Scanner Class

Before using Scanner, import it using:

import java.util.Scanner;

This statement tells Java that we want to use the Scanner class.

Creating a Scanner Object

After importing Scanner, create an object:

Scanner sc = new Scanner(System.in);

Explanation

• Scanner → Class name

• sc → Object name

• new → Creates a new object

• System.in → Reads input from the keyboard

Taking Integer Input

Example:

import java.util.Scanner; public class InputExample { 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("Age = " + age); } }

Sample Output

Enter your age: 20
Age = 20

Taking Floating-Point Input

Using float

float percentage = sc.nextFloat();

Using double

double salary = sc.nextDouble();

Taking String Input

Using next()

next() reads only one word.

Example:

String name = sc.next(); System.out.println(name);

Input:

Rahul

Output:

Rahul

If the user enters:

Rahul Kumar

Output:

Rahul

Only the first word is read.

Using nextLine()

nextLine() reads the entire line, including spaces.

Example:

String fullName = sc.nextLine(); System.out.println(fullName);

Input:

Rahul Kumar

Output:

Rahul Kumar

Taking Character Input

Scanner does not provide a direct method for reading a character.

Instead, use:

char grade = sc.next().charAt(0);

Example:

System.out.print("Enter Grade: "); char grade = sc.next().charAt(0); System.out.println("Grade = " + grade);

Complete Example

import java.util.Scanner; public class StudentDetails { public static void main(String[] args) { Scanner sc = new Scanner(System.in); System.out.print("Enter Name: "); String name = sc.nextLine(); System.out.print("Enter Age: "); int age = sc.nextInt(); System.out.print("Enter Percentage: "); double percentage = sc.nextDouble(); System.out.print("Enter Grade: "); char grade = sc.next().charAt(0); System.out.println("\n------ Student Details ------"); System.out.println("Name : " + name); System.out.println("Age : " + age); System.out.println("Percentage : " + percentage); System.out.println("Grade : " + grade); sc.close(); } }

Sample Output

Enter Name: Rahul Kumar
Enter Age: 20
Enter Percentage: 89.5
Enter Grade: A

------ Student Details ------
Name       : Rahul Kumar
Age        : 20
Percentage : 89.5
Grade      : A

Scanner Methods

Difference Between next() and nextLine()

Common Mistakes

Forgetting to Import Scanner

Incorrect:

Scanner sc = new Scanner(System.in);

Compilation Error

Correct:

import java.util.Scanner;

Forgetting to Create Scanner Object

Incorrect:

int age = sc.nextInt();

Correct:

Scanner sc = new Scanner(System.in);

int age = sc.nextInt();

Mixing nextInt() and nextLine()

Example:

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

The nextLine() may be skipped because nextInt() leaves a newline character in the input buffer.

Solution:

int age = sc.nextInt();
sc.nextLine();

String name = sc.nextLine();

Forgetting to Close Scanner

Good practice:

sc.close();

This releases system resources after input is complete.

Best Practices

• Import java.util.Scanner before using Scanner.

• Create only one Scanner object for keyboard input.

• Close the Scanner object after use.

• Use nextLine() when reading sentences or names with spaces.

• Display clear prompts before accepting user input.

Key Points to Remember

• Scanner is used to read user input.

• It belongs to the java.util package.

• Import Scanner before using it.

• next() reads one word.

• nextLine() reads an entire line.

• Always close the Scanner object after use.

Lesson Summary

In this lesson, you learned:

• What the Scanner class is.

• How to import and create a Scanner object.

• How to read integers, decimal numbers, characters, and strings.

• The difference between next() and nextLine().

• Common mistakes and best practices when using Scanner.

Using the Scanner class allows you to create interactive Java programs where users can provide their own input.

Practice Questions

1. What is the Scanner class?

2. Which package contains the Scanner class?

3. How do you create a Scanner object?

4. What is the difference between next() and nextLine()?

5. Which method reads an integer?

6. How do you read a character using Scanner?

7. Why should sc.close() be used?

8. What problem occurs when using nextInt() followed by nextLine()?

Programming Exercise

Write Java programs to:

1. Read your name and print it.

2. Read your age and print it.

3. Read two numbers and display their sum.

4. Read your percentage and display it.

5. Read your grade and print it.

6. Read your full address using nextLine().

Assignment

Create a program named StudentRegistration.java that accepts the following details from the user:

• Student Name

• Roll Number

• Age

• Department

• Semester

• Percentage

• Grade

Display all the entered information in a neatly formatted output.

Next Lesson: Lesson 2.7 – Practice Programs