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

[sophiarobart]

Java is one of the most popular programming languages used for everything from desktop applications to web applications. One of the tasks you will commonly perform while writing Java programs is collecting user input, and the Scanner class is likely one of the first options that beginners and professional Java developers will use, since the Scanner class is easy to use. While the Scanner class is easy to use, one important thing that most beginners fail to do is correctly close the Scanner object.



In this article, we’ll explain how to close a Scanner in Java, why it matters, and the best way to do it to prevent any resource leaks or issues down the line.


Understanding the Scanner Class


Before we venture into closing the Scanner, we shall take a quick look at what the Scanner is. Scanner class belongs to the package, that is, java.util and is usually employed to read the input on various sources such as the console (System.in), files or strings.


Below is a simple example of application of a Scanner:

javaimport java.util.Scanner;public class UserInputExample {    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);        // scanner.close(); // We'll talk about this next    }}

Although this is working well, missing something occurs, the Scanner is supposed to be closed.


Why Closing Scanner is Important


Java, as most programming languages, utilizes system resources in order to complete input/output operations. Once you open a resource such as a file, socket or input stream, it consumes memory and underlying OS handles. Provided these are not released correctly, you can have problems with performance, or the system can crash in the long run.


At this point, the idea of Java resource management Scanner close comes in play.


Leakage of memory may happen when you fail to close your Scanner, particularly when reading a file or a network stream. Things will not be cleaned immediately or predictably even though the garbage collector will come and do it later.


As a matter of fact, in case of the use of System.in as the source, closing Scanner will automatically close System.in that cannot be reopened in the course of the running. That is why, it is necessary to know when and how to close it properly.


How to Close Scanner in Java


It is easy to close a Scanner. The class carries out Closeable and thus there is a close method. A Scanner can be closed, such as:

Scanner scanner = new Scanner(System.in);// Use the scannerscanner.close();

That is it, however, there is more to it, particularly with regard to the source of the input.


Don’t Close Scanner on System.in Prematurely


Often when your application opens System.in more than once, the closing of the Scanner will also close System.in, preventing further input. In these cases:

• Do not switch the Scanner off at once.
  
• Think about writing one Scanner to live with your program.
  
• As an alternative, enclose input reading logic in a method and handle input centrally.
  

Common Pitfalls to Avoid

• Double closing: Do not attempt to close a Scanner twice. It will not bring your program to its knees, yet it is not necessary.
  

• Scanner on System.in: Does not close too soon when you want to read later.
  

• Now forget try-with-resources: Manual closing is error prone. Where possible, use try-with-resources because it is safer and cleaner.
  

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Conclusion


Good programming hygiene means managing the resources well. You may be reading the console, a file or any other resource, but it is critical to know how to close Scanner in Java properly. Failure to do so may lead to nuanced bugs and performance problems - e.g. a Scanner closing memory leak Java case.

[herry33]

Very user-friendly guide! Many people forget to turn off Scanner in Java, which can cause memory leaks or waste resources. This post explains the issue in a simple way, just like Fix My Speaker, which is really helpful for beginners.