Programming & Coding Tips

How to Close Scanner in Java: A Comprehensive Guide for Beginners

2025-05-28

Table Of Content

When working with Java, the Scanner class allows you to read information from the console, from files and also from strings. Because it adapts so well, developers often use it to take care of user input and work with data. However, there is an important task that is easy to forget: ending the Scanner correctly. It matters a lot to know how to close a Scanner in Java, because failing to do so can result in resource leaks that harm a program and the stability of the computer system.

We will discuss how to close a Scanner, explain why it helps your code be neater and avoid common pitfalls. We will explain how to make use of the Scanner class and correctly close it when appropriate. Additionally, we’ll answer top questions that might help solve anyone’s remaining doubts. If you’re a beginner or an expert, the guide teaches you the best ways to ensure your Java code is trusted.

Understanding the Scanner Class in Java

You can find the Scanner class in java.util, and it is normally used to get information from the keyboard, files, and strings. Knowing this tool is necessary for developers who make interactive applications. The Scanner is able to read both primitive types and strings using regular expressions, giving you flexible ways to accept user input.

Creating a Scanner typically means setting its source of input in the instantiation process. For example, you would use ‘new Scanner(System.in)’, if you want to read from the console. When the Scanner object is made, you can access methods like `nextInt()`, `nextFloat()` and `nextLine()` to receive user input as the required type.

A main advantage of the Scanner class is that it efficiently handles different kinds of input. As a result, data can easily be viewed as integers, floats or text which saves users from facing complicated parsing problems. Just remember, once you’re done using a Scanner, it’s a good practice to close scanner java with the `close()` method to avoid any resource leaks

Here’s an easy example showing how you can use the Scanner class to capture both integer and string values:

Code Snippet	Description
‘Scanner scanner = new scanner(System.in);’	Creates a new Scanner object for console input.
‘int number = scanner.nextInt();’	Reads an integer input from the user.
‘scanner.close();’	Closes the Scanner to prevent resource leaks.

When Scanner is handled wisely by developers, it can help create flexible applications that improve how input is managed for users.

How to Close a Scanner in Java

Closing a ‘Scanner’ after using it allows your system to free up important resources and helps to avoid memory leaks. It is the ‘Scanner’ class that reads both primitive types and strings using regular expressions, manages input streams and makes sure everything is done within system resources. Being sure to close any InputStream that creates a ‘Scanner’ is very important.

In order to close scanner in java, call the ‘close()’ method using the ‘Scanner’ object. With this approach, you can’t use the same input source, for example, System.in, to read more input in the same program.

An example that demonstrates how to use and close a ‘Scanner’ is shown below.

import java.util.Scanner;
public class CloseScanner {
public static void main(String[] args) {
Scanner scanner = null;
try {
scanner = new Scanner(System.in);
System.out.print("Enter something: ");
String input = scanner.nextLine();
System.out.println("You entered: " + input);
} finally {
if (scanner != null) {
scanner.close();
}
}
}
}

In the example, a Scanner object is established to handle getting data from the user. Reading and processing input are done inside the ‘try’ block and the ‘Scanner’ will always be closed in the ‘finally’ block, no matter what. Bringing down the scanner object as soon as it’s possible helps you prevent leaks and maintain proper resource management in your program.

Why Closing a Java Scanner Matters

Resource Management: After you finish with the scanner, don’t forget to close it and stop it from using so many resources. A Scanner uses the resources of your PC while it’s running, so when you’re finished with it, make sure not to leave its resources occupied.
Preventing Memory Leaks: Leaky Scanners can be avoided by remembering to close them correctly after you are done using them. Consequently, it can negatively impact the performance and stability of reliable applications kept running for a long time.
Input Stream Closure: The Java close scanner also close the input stream it ties into. When a Scanner gets input from `System.in`, it is not possible to reuse it after closing. Proper organizational finishes help avoid unexpected issues as other parts of the program run.
Predictable Application Behavior: Closing Scanners as they should be helps your program keep normal behavior. Closing a Scanner after use is important or else your program may behave strangely if it tries to read past that point.
Best Practice: It is recommended to use a ‘try-with-resources’ statement or a ‘finally’ block so that the Scanner is closed no matter what happens. As a result, the code is more dependable and hassle-free to maintain.
Efficiency in Resource Use: If you shut down your scanner after finishing your task, your program will operate more efficiently and you will save system resources.

Closing Scanners regularly improves how resources are used, safeguards against memory leaks and guarantees an expected behavior from your apps. When developers use this method, the Java applications they create are stronger and run more smoothly.

Best Practices for Using and Closing Scanner

1. Always Close the Scanner:

After you’re done using the Scanner, make sure to close it with the `close()` method. As a result, memory leaks are reduced and the system can handle other work.

2. Use Try-with-Resources:

In Java 7 or later, always use the try-with-resources statement. As a result, the Scanner is automatically shut down at the end of the statement, so resources are available at any time, whether there are any errors or not. For example:

try (Scanner scanner = new Scanner(System.in)) {
// your code here
} // scanner is automatically closed here

3. Avoid Closing System.in:

If you use System.in, do not close the scanner, as doing so will close the entire input stream. This will stop further reads from the console in the same application.

4. Handle Exceptions Gracefully:

If you're working with Scanner operations, it's a good idea to use try-catch blocks to manage any potential exceptions, like NoSuchElementException or InputMismatchException.

5. Use a Single Scanner Instance:

Instead of making multiple Scanner instances for the same input source, use only one to read. This method helps reduce the use of resources and the problems linked to inputs.

6. Check for Input Validity:

Before starting to process input, run methods like `hasNextInt()`, `hasNextLine()`, etc., to be sure that the input from the user is valid. It stops errors from happening during runtime which improves what users get.

7. Consider Input Types:

Be careful to know which form of data each user should provide. Apply the correct method (like `nextInt()`, `nextDouble()` or `nextLine()`) for input readings to avoid errors.

8. Keep Resource Management in Mind:

Planning how and when to manage resources is always useful. Closing Scanners correctly allows long-running applications to work without any memory problems.

9. Document Scanner Usage:

Be sure to add comments that explain your usage of Scanner and especially the closing of it. By doing this, your message stays understandable and easy to look over in the future.

By sticking to these best practices, you can make the most out of the Scanner class while keeping your Java applications running smoothly and reliably.

Common Mistakes When Closing Scanner

The common mistakes that one must avoid when closing a scanner are mentioned below in detail:

Not Closing the Scanner: Too often, people forget to close the Scanner once they’re done. It can trigger resource wastage and memory problems and this situation often lowers the app’s performance in the long run.
Closing System.in: Closing a scanner that is reading from System.in will halt the reading from the related input stream. When this happens, `System.in` can no longer accept any further input. Developers often unintentionally close the scanner when they still plan to read what the user is entering.
Closing Scanner Too Late: You should remember to close a Scanner when the process is over, especially in a long routine. Be sure to close the connection when it’s finished which should happen in a `finally` section or with try-with-resources.
Closing Scanner Too Early: If you close a Scanner before it has finished reading all the input, you may get ‘NoSuchElementException’ or ‘IllegalStateException’. If you close the Scanner before all the necessary input is collected, you won’t be able to read data from it anymore. You should leave the Scanner tool open until you input is complete.
Using Multiple Scanners on the Same Input Stream: When several Scanner instances are created from the same input source, unexpected problems can occur. It is better to use the same Scanner throughout the stream, rather than creating duplicates that could conflict.
Ignoring Exceptions: Not dealing with Scanner errors when closing can leave the process running improperly.
Not Using Try-With-Resources: Previous Java codes might have neglected the try-with-resources statement that closes resources for you. If you don’t use this feature, it can cause more unnecessary code and a higher risk of skipped resource management.
Assuming That Scanner Is Thread-Safe: Scanner is not designed for use in multithreaded situations. Using the same Scanner instance in several threads without synchronization may cause changes in the system that are out of sync.

Being aware of these usual problems allows developers to improve the stability and running of Java applications with Scanners.

Practical Examples of Using and Closing Scanner

Below are practical examples of using and closing a ‘Scanner’, along with explanations of each example's purpose.

Example 1: Reading User Input from the Console

import java.util.Scanner;

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

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

System.out.println("Hello, " + name + "!");

// Closing the Scanner
scanner.close();
}
}

It illustrates how to set up a `Scanner` to read what users type in the console. The software asks the user to type in their name. As soon as input is provided, a greeting message pops up.

Example 2: Reading from a File

import java.io.File;

import java.util.Scanner;

public class Example {

public static void main(String args[]) throws Exception {

//Creating the File object

File file = new File("D:\Softteco.txt");

//Creating a Scanner object

Scanner scanner = new Scanner(file);

//verify whether the file has another line

while(scanner.hasNext()) {

//reads, returns and prints the next line in the file.

String str = scanner.nextLine();

System.out.println(str);

}

The aim of this sample is to read every line from a specified text file using a Scanner and illustrate how to handle Java file input when you need to check for more lines after processing the first.

Example 3: Reading Multiple Inputs in a Loop

import java.util.Scanner;

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

System.out.println("Enter text (type 'exit' to quit):");
while (!(input = scanner.nextLine()).equalsIgnoreCase("exit")) {
System.out.println("You entered: " + input);
}

// Closing the Scanner
scanner.close();
}
}

Here is an example of reading various lines of input one at a time until an exit command called "exit" is typed. Such a feature is useful when users interact with an application regularly.

Conclusion

All things considered, learning how to end a Scanner in Java matters for strong and effective development. If developers close Scanners as soon as they can and use try-with-resources, they can stop resource leaks and better control memory. If you don’t close a Scanner, you may face unpredictable application behaviors, memory leaks and lower performance. Besides, you should prevent frequent errors, for instance, by not using System.in for input nor creating multiple Scanners for the same stream in Java. When programmers master these techniques, users find application interface easier and the Scanner class is put to its best use in the program.

FAQs

Q. How do you import Scanner in Java?

Ans. The Scanner class can be imported in Java by writing ‘import java.util.Scanner’ in your Java file. Code efficiency is improved because the Scanner is flexible and can get input from the console, files or strings.

Q. How to use Scanner for different data types?

Ans. You should use specific methods of Scanner to get data for different types.

For integers, use ‘int num = scanner.nextInt();’.
Use ‘String text = scanner.nextLine();’ when handling strings.
Use ‘double value = scanner.nextDouble();’ to read floating-point numbers.

With these methods, users can handle data more flexibly.

Q. Is it necessary to close Scanner in Java?

Ans. Yes, it is important to shut down the Scanner most of the time so that no resources are left unused. When the Scanner is closed, the system frees up resources used for input, making sure the application works better and more efficiently.

Q. What happens if you don’t close a Scanner?

Ans. If you don’t close a Scanner linked to a file, you could get memory leaks or errors you did not plan for. Over time, this situation can slow down an application and it could even disrupt the performance of later input.

Q. How to use Scanner in Java Eclipse or VSCode?

Ans. It is easy to use Scanner in Java, either in Eclipse or VSCode. Create your Java files using the familiar syntax and be sure you have the right Java installation. Add a Scanner at the top of your file, and then set up a Scanner object to handle reading user input when needed.

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