Input from Keyboard (Scanner Class) in Java

Overview

Taking input from the keyboard is a common requirement in many Java applications. The Scanner class, available in the java.util package, provides a simple way to read input from the keyboard. This tutorial covers the basics of using the Scanner class to read different types of data from the user.

Importing the Scanner Class

To use the Scanner class, you need to import it from the java.util package.

Example:

import java.util.Scanner;

Creating a Scanner Object

After importing the Scanner class, you can create a Scanner object to read input from the keyboard.

Syntax:

Scanner scanner = new Scanner(System.in);

Example:

import java.util.Scanner;

public class InputExample {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.println("Enter your name:");
        String name = scanner.nextLine();
        System.out.println("Hello, " + name + "!");
    }
}

Reading Different Types of Data

The Scanner class provides various methods to read different types of data from the keyboard:

• nextLine(): Reads a string of text.
• nextInt(): Reads an integer.
• nextDouble(): Reads a double.
• nextBoolean(): Reads a boolean.

Example:

import java.util.Scanner;

public class InputExample {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        System.out.println("Enter your age:");
        int age = scanner.nextInt();

        System.out.println("Enter your height (in cm):");
        double height = scanner.nextDouble();

        System.out.println("Are you a student? (true/false):");
        boolean isStudent = scanner.nextBoolean();

        System.out.println("You entered - Age: " + age + ", Height: " + height + " cm, Student: " + isStudent);
    }
}

Handling Input Errors

When reading input from the keyboard, you may encounter input errors if the user enters data of the wrong type. To handle such errors, you can use try-catch blocks.

Example:

import java.util.Scanner;

public class InputExample {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        try {
            System.out.println("Enter your age:");
            int age = scanner.nextInt();
            System.out.println("You entered: " + age);
        } catch (Exception e) {
            System.out.println("Invalid input. Please enter an integer.");
        }
    }
}

Closing the Scanner

It is a good practice to close the Scanner object after you are done using it to free up system resources.

Example:

import java.util.Scanner;

public class InputExample {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        System.out.println("Enter your name:");
        String name = scanner.nextLine();
        System.out.println("Hello, " + name + "!");

        // Close the scanner
        scanner.close();
    }
}

Summary

In this tutorial, you learned how to use the Scanner class to read input from the keyboard in Java. The Scanner class provides a simple way to read different types of data, including strings, integers, doubles, and booleans. You also learned how to handle input errors and the importance of closing the Scanner object. Properly handling user input is essential for building interactive Java applications.