Scanner Class In Java

In Java, there are multiple methods available for obtaining input from users. One of these methods involves utilizing the Scanner class. This approach is considered the most straightforward means of collecting user input. The Scanner class in Java is a component of the java.util package.

The Scanner class divides the input into tokens based on a specified delimiter, with whitespace being the default delimiter. It offers a range of methods for reading and interpreting different primitive data types.

The Scanner class is commonly employed for parsing text to extract strings and primitive data types through regular expressions. This class facilitates reading user input in various primitive types like int, long, double, byte, float, short, and more.

The Java Scanner class is an extension of the Object class and also incorporates the Iterator and Closeable interfaces.

In Java, the Scanner class offers various nextXXX functions to retrieve different types of values like integers using nextInt, bytes using nextByte, shorts using nextShort, strings using next, entire lines using nextLine, double values using nextDouble, float values using nextFloat, boolean values using nextBoolean, and more. If we need to extract a single character from the scanning process, we can utilize the next.charAt(0) operation to obtain a single character.

Java Scanner Class Declaration

public final class Scanner extends Object implements Iterator<String>

How to get a Java Scanner?

In order to create an object of the Java Scanner class that can read user input, it is necessary to provide the input stream (System.in) as an argument in the Scanner class constructor. For instance:

Scanner in = new Scanner(System.in);

In order to obtain an instance of Java Scanner that analyzes strings, it is necessary to provide the strings as arguments in the constructor of the Scanner class. For instance:

Scanner in = new Scanner("Hello Exampletech");

Java Scanner Class Constructors

Java Scanner Class Methods

The Java Scanner class offers a variety of methods as outlined below.

Example-1

Consider this basic illustration of Java Scanner demonstrating the acquisition of a solitary user input. In this scenario, we are prompting the user to provide a string using the in.nextLine function.

import java.util.*;  

public class Main {  

public static void main(String args[]){  

          Scanner in = new Scanner(System.in);  

          System.out.print("Enter your name: ");  

          String name = in.nextLine();  

          System.out.println("Name is: " + name);             

          in.close();             

          }  

}

Output:

Enter your name: Jack

Name is: Jack

Example-2

import java.util.*;  

public class Main {    

      public static void main(String args[]){                       

          String s = "Hello, Welcome to C# Programming.";  

          //Create a scanner Object and pass the string into it  

          Scanner scan = new Scanner(s);  

          //Check if the scanner has a token  

          System.out.println("Boolean Result: " + scan.hasNext());  

          //Print the string  

          System.out.println("String: " +scan.nextLine());  

          scan.close();           

          System.out.println("--------Enter Your Details-------- ");  

          Scanner in = new Scanner(System.in);  

          System.out.print("Enter your name: ");    

          String name = in.next();   

          System.out.println("Name: " + name);           

          System.out.print("Enter your age: ");  

          int i = in.nextInt();  

          System.out.println("Age: " + i);  

          System.out.print("Enter your salary: ");  

          double d = in.nextDouble();  

          System.out.println("Salary: " + d);         

          in.close();           

          }    

}

Output:

Boolean Result: true

String: Hello, Welcome to C# Programming.

-------Enter Your Details---------

Enter your name: Andrew

Name: Andrew

Enter your age: 23

Age: 23

Enter your salary: 25000

Salary: 25000.0

Example-3

import java.util.*;  

public class Main {    

      public static void main(String args[]){                       

          String str = "Hello/This is C# Tutorial/My name is Jack.";  

          //Create scanner with the specified String Object  

          Scanner scanner = new Scanner(str);  

          System.out.println("Boolean Result: "+scanner.hasNextBoolean());            

          //Change the delimiter of this scanner  

          scanner.useDelimiter("/");  

          //Printing the tokenized Strings  

          System.out.println("---Tokenizes String---");   

        while(scanner.hasNext()){  

            System.out.println(scanner.next());  

        }  

          //Display the new delimiter  

          System.out.println("Delimiter used: " +scanner.delimiter());            

          scanner.close();  

          }    

}

Output:

Boolean Result: false

---Tokenizes String---

Hello

This is C# Tutorial

My name is Jack.

Delimiter used: /

Advantages of Scanner Class

• ✅ User-Friendly: The Scanner provides a simple and intuitive way to read input, especially for beginners.
• ✅ Built-in Parsing: It can directly parse primitive data types (for example, int, double, and boolean) from the input without requiring manual conversion.
• ✅ Flexible Input Sources: The scanner can read input from multiple sources like System, in, strings, files, and streams.
• ✅ Tokenization Support: It splits input into tokens based on delimiters, which can be customized using useDelimiter.
• ✅ Convenient Methods: Provides hasNextXxx methods to validate input types before reading, helping avoid input mismatch exceptions.

Disadvantages of Scanner Class

• ✅ Performance Overhead: Scanner is relatively slower compared to BufferedReader, especially when processing large amounts of data.
• ✅ Locale Sensitivity: Parsing numbers depends on the default or set Locale, which may lead to unexpected behaviour in different regions.
• ✅ next vs nextLine Confusion: It often confuses beginners since next reads up to space, whereas nextLine reads the full line, causing input skipping issues.
• ✅ Limited Formatting Control: The scanner lacks advanced formatting options available in other input methods (like BufferedReader + InputStreamReader).
• ✅ Resource Management: Improper use (like closing System.in) can lead to input stream errors in other parts of the application.

Important Points to Remember

• ✅ Import Required: Always import java.util.Scanner before using the Scanner class.
• ✅ Default Delimiter: Scanner uses whitespace as the default delimiter. Use useDelimiter to change it.
• ✅ Primitive Inputs: The scanner can read various primitive types like int, double, float, long, short, byte, and also boolean.
• ✅ String Input Differences: next reads only a single word (token). nextLine reads the entire line including spaces.
• ✅ Resource Handling: Always close the Scanner using in.close to avoid resource leaks.
• ✅ Token Checking: Use hasNext, hasNextInt, hasNextDouble, etc., to check the next token before reading to avoid runtime exceptions.
• ✅ Reading a Single Character: Use in.next.charAt(0) to read a single character.
• ✅ next reads only a single word (token).
• ✅ nextLine reads the entire line including spaces.

Conclusion

The Scanner class in Java is a useful tool that enables programs to receive input from various sources such as the keyboard, files, or strings. It plays a crucial role in console-based applications by facilitating the processing of diverse data types like strings, integers, floats, and booleans.

Developers can easily obtain user input using methods like next, nextLine, nextInt, and nextDouble. The Scanner class in Java is valuable for its flexibility in handling delimiters and performing type checking, making it a beneficial tool for programming tasks.

When developing a basic command-line application or handling text data in Java, incorporating the Scanner class facilitates a straightforward and secure approach to receiving input.

Scanner Class MCQs

1. Which package contains the Scanner class in Java?

• ✅ java.io
• ✅ java.lang
• ✅ java.util
• ✅ java.text

Explanation: The Scanner class is part of the java.util package, and it is commonly used to take input from various sources like input streams, strings, and files.

1. What does the Scanner class use as the default delimiter?

• ✅ , (comma)
• ✅ ; (semicolon)
• ✅ Whitespace
• ✅ Newline (\n)

Explanation: By default, the Scanner class splits input into tokens based on whitespace characters (spaces, tabs, newlines).

1. Which method is used to read an entire line of text input using Scanner?

• ✅ next
• ✅ readLine
• ✅ nextString
• ✅ nextLine

Explanation: nextLine reads the entire line including spaces, until the newline character is encountered.

1. What does the method next.charAt(0) return?

• ✅ The next token as a String
• ✅ The first character of the next token
• ✅ A character array of the input
• ✅ The ASCII code of the first character

Explanation: next returns the next token as a String. Calling charAt(0) on it gives the first character of that token.

1. What will happen if you call in.nextInt and the input is not a valid integer?

• ✅ It throws NumberFormatException
• ✅ It throws an InputMismatchException
• ✅ It returns 0
• ✅ It skips the input

When the method nextInt is invoked with an input that is not a valid integer, the Scanner class will raise an InputMismatchException.