Java Scanner Class

The Scanner class is a powerful utility in the java.util package, designed to read input from various sources, including the keyboard, files, and more. It simplifies the process of parsing primitive types and strings through regular expressions.

Key Concepts

• Purpose: The Scanner class primarily serves to obtain input from users, allowing for easy reading of different data types.
• Input Sources: It can read input from various sources, including:
  • Keyboard (standard input)
  • Files
  • Strings
  • Streams

How to Use Scanner

1. Reading Input: Use various methods provided by the Scanner class to read different input types:
   • nextInt(): Reads an integer value.
   • nextDouble(): Reads a double value.
   • nextLine(): Reads an entire line as a string.
   • next(): Reads the next token (word).

Create a Scanner Object: Instantiate a Scanner object by passing the desired input source.

Scanner scanner = new Scanner(System.in); // For keyboard input

Import the Scanner Class: First, you need to import the Scanner class to utilize it in your program.

import java.util.Scanner;

Example

Below is a simple example demonstrating how to read user input using the Scanner class:

import java.util.Scanner;

public class ScannerExample {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        
        System.out.print("Enter your name: ");
        String name = scanner.nextLine(); // Read a string
        
        System.out.print("Enter your age: ");
        int age = scanner.nextInt(); // Read an integer
        
        System.out.println("Hello, " + name + "! You are " + age + " years old.");
        
        scanner.close(); // Close the scanner
    }
}

Important Notes

• Closing the Scanner: Always remember to close the Scanner object using scanner.close() to free up system resources.
• Input Mismatch: Exercise caution with input types. An attempt to read a different type than what was inputted may result in an InputMismatchException.

Conclusion

The Scanner class is an essential tool for handling input in Java. By mastering its basic methods and understanding how to create a Scanner object, beginners can effectively read and process user input in their applications.