Scanner Class in Java

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Introduction

The Java Scanner class is a simple text scanner that can parse primitive types (int, double, long, etc.) and strings using regular expressions. The Scanner class plays an important role in Java by providing user-based input.

The Scanner class is a part of java.util package, and a scanner can read text from any object that implements the Readable interface. When we close a Scanner, it will close its input source if the source implements the Closeable interface.

Characteristics of the Scanner class

The following are some of the important characteristics of the Scanner class in Java −

• A Scanner breaks its input into tokens using a delimiter pattern, which by default matches whitespace.
• A scanning operation may block while waiting for input.
• A Scanner is not safe for multithreaded use without external synchronization.

Class declaration

F ollowing is the declaration for the Scanner class −

public final class Scanner
extends Object
implements Iterator<String>

How to use the Scanner Class?

The scanner class can be used by following the steps below −

Step 1

The first and important step is to import the java.util.Scanner at the top of our code, as without the Scanner class, we cannot use its methods. We can either use the java.uti.Scanner or java.util.* package to work with the Scanner class.

import java.util.Scanner
//OR
import java.util.*

Step 2

The second step is to create the object of the Scanner class. Here, the "sc" is the Scanner class object, and it allows the user to read from the System. To create an object of the Scanner class, call the Scanner() constructor.

Scanner sc = new Scanner(System.in);

Step 3

The third step is to create a variable, and on that variable, use the methods from the Scanner class object to take user input.

int number = sc.nextInt();

After using the Scanner class, use the close() method to close the Scanner operations.

Example

Below is an example of how to input a number using the Scanner class in Java −

//Step 1: import the Scanner class
import java.util.Scanner;

public class DemoScanner {
    public static void main(String[] args) {
        // Step 2: Create Scanner object
        Scanner sc = new Scanner(System.in);
        System.out.print("Enter a number: ");

        // Step 3: Read the number from console 
        int number = sc.nextInt();
        System.out.println("The entered number is: " + number);

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

Output

This will produce the following result −

Enter a number: 10
The entered number is: 10

Uses of Scanner Class

The following are some of the use cases of the Scanner class in Java −

• The Scanner class is used for reading and analyzing data stored in text files(logs, configuration files).
• Helps developers in building console-based applications, such as a Student management system.
• It can also be used to parse tokens, which helps in Data Parsing from CSV files.

Class constructors

The following are the Scanner class constructors present in Java −

Class methods

The following are the Scanner class methods present in Java −

Methods inherited

This class inherits methods from the following classes −

• java.util.Object

Reading a Line from Console using Scanner Class Example

The following example shows the usage of Java Scanner nextLine() to read a line from the Console and the close() method to close the scanner. We've created a scanner object using a given string. Then we printed the string using the nextLine() method, and then the scanner was closed using the close() method.

package com.tutorialspoint;

import java.util.Scanner;

public class ScannerDemo {
   public static void main(String[] args) {

      String s = "Hello World! 3 + 3.0 = 6";

      // create a new scanner with the specified String Object
      Scanner scanner = new Scanner(s);

      // print the next line of the string
      System.out.println(scanner.nextLine());

      // close the scanner
      System.out.println("Closing Scanner...");
      scanner.close();
      System.out.println("Scanner Closed.");
   }
}

Output

This will produce the following result −

Hello World! 3 + 3.0 = 6
Closing Scanner...
Scanner Closed.

Handling Mixed Inputs in Scanner Class

When working with multiple inputs like nextInt(), nextDouble(), nextFloat(), they do not need a newline (\n) character after pressing the Enter key. This creates a problem when taking string input after them, as they take an empty string between them, creating issues in the code. So, to handle this issue, always add a sc.nextLine() in between number and string inputs.

Example

Below is an example for handling mixed inputs using the Scanner Class in Java −

import java.util.Scanner;

public class ScannerDemo {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        System.out.print("Enter your age: ");
        int age = sc.nextInt();
        
        // Handling the newline issue
        sc.nextLine();
        System.out.print("Enter your name: ");
        String name = sc.nextLine();
        System.out.print("Enter your salary: ");
        double salary = sc.nextDouble();

        System.out.println("Name: " + name);
        System.out.println("Age: " + age);
        System.out.println("Salary: " + salary);

        sc.close();
    }
}

Output

This will produce the following result −

Enter your age: 23
Enter your name: Akash
Enter your salary: 23403.75

Name: Akash
Age: 23
Salary: 23403.75