JAVA

User Input

So far, all the values in our programs have been hardcoded. For example, if a program stores a user's name or age, those values are written directly into the code. While this is useful for learning, real applications need to accept information from users while the program is running.

For example, a banking application asks for an account number, an e-commerce website asks for a delivery address, and a login page asks for a username and password. To make programs interactive, Java provides ways to read input from the user.

In this chapter, you will learn how to accept input from the keyboard using the Scanner class and store the entered values in variables.

What is User Input?

User input is any information entered by a user while a program is running.

Examples:

• Name
• Age
• Marks
• Mobile Number
• Password
• Product Quantity

Instead of hardcoding values, we can ask the user to provide them.

The Scanner Class

Java provides the Scanner class to read input from the keyboard.

Before using Scanner, it must be imported.

import java.util.Scanner;

This gives our program access to the Scanner class.

Creating a Scanner Object

To read input, create a Scanner object.

Scanner sc = new Scanner(System.in);

Here:

• Scanner is the class name.
• sc is the object name.
• System.in represents keyboard input.

For now, simply remember:

Scanner sc = new Scanner(System.in); is used to read input from the keyboard.

Reading a String

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 name: ");

        String name = sc.nextLine();

        System.out.println("Hello " + name);
    }
}

Input:

Rahul

Output:

Enter your name: Rahul
Hello Rahul

Understanding the Code

String name = sc.nextLine();

This line reads a complete line of text entered by the user and stores it in the variable name.

Reading an Integer

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("Your age is " + age);
    }
}

Input:

18

Output:

Enter your age: 18
Your age is 18

Understanding the Code

int age = sc.nextInt();

This line reads an integer value from the keyboard and stores it in the variable age.

Reading a Decimal Number

Example:

double price = sc.nextDouble();

This reads a decimal number such as:

99.99

and stores it in a double variable.

Common Input Methods

Common Mistakes

Forgetting to Import Scanner

Wrong:

Scanner sc = new Scanner(System.in);

Without:

import java.util.Scanner;

Java will show an error.

Reading the Wrong Data Type

int age = sc.nextInt();

If the user enters:

Rahul

Java will throw an error because nextInt() expects a number.

Key Takeaways

• User input makes programs interactive.
• Java uses the Scanner class to read input.
• System.in represents keyboard input.
• nextLine() reads text.
• nextInt() reads integers.
• nextDouble() reads decimal values.
• Input values can be stored in variables and used throughout the program.