Java Scanner Class Example in Java

Introduction

The Scanner class in java.util is the most common way to read keyboard input in beginner Java programs. It can read integers, floating-point numbers, words and entire lines from System.in.

When to Use Scanner

Use Scanner when your program needs interactive input from the user — for example, reading a name, age or menu choice in a console application.

Example Program

import java.util.Scanner;

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

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

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

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

        System.out.println("\n--- Profile ---");
        System.out.println("Name   : " + name);
        System.out.println("Age    : " + age);
        System.out.println("Height : " + height + " cm");

        sc.close();
    }
}

Sample Output

Enter your name: Thiyagaraaj
Enter your age: 25
Enter your height (cm): 172.5

--- Profile ---
Name   : Thiyagaraaj
Age    : 25
Height : 172.5 cm

How It Works

1. new Scanner(System.in) connects the scanner to standard input (keyboard).
2. nextLine() reads a full line of text including spaces.
3. nextInt() and nextDouble() parse numeric tokens from the input stream.
4. Always call close() when finished to release the underlying stream.

Best Practices

• Import java.util.Scanner explicitly in exam and interview programs.
• After nextInt() or nextDouble(), consume the trailing newline with an extra nextLine() if you read text next.
• Do not create multiple Scanner objects on System.in in the same program.

Common Mistakes

• Mixing next() and nextLine() without understanding token boundaries.
• Forgetting to close the scanner in long-running applications.
• Using Scanner for file parsing when dedicated readers (BufferedReader, Files.lines) are more efficient.