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Java User Input Essentials

bookClosing the Scanner and Best Practices

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Before you finish working with user input in Java, it is important to understand the concept of resource management. When you create a Scanner object to read input, especially from the keyboard using System.in, you are opening a connection to a resource provided by the operating system. If you do not close this resource when you are done, your program may continue to hold on to system resources longer than necessary. This can lead to issues such as memory leaks or running out of available resources if your program creates many Scanner objects over time. Properly closing resources is a fundamental part of responsible programming, ensuring your applications are efficient and do not cause unnecessary problems for the system or other programs.

Main.java

Main.java

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package com.example;
import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.println("Enter your name:");
        String name = scanner.nextLine();
        System.out.println("Hello, " + name + "!");
        scanner.close();
    }
}

When working with Scanner, you should always close it after you are finished reading input. In small programs, like a simple command-line tool, you can call scanner.close() at the end of your program, after all user input is processed. This releases the underlying resource and is generally considered good practice.

In larger programs, especially those that handle multiple resources or perform many operations, it is better to use a try-with-resources statement (introduced in Java 7) to ensure your Scanner is always closed, even if an exception occurs. However, you should be careful when closing a Scanner that wraps System.in, because closing it will also close the underlying input stream, making further input impossible for the rest of the program. If your application needs to read input from System.in in multiple places, you should create a single Scanner and close it only when all input is complete.

Remember these best practices:

  • Always close your Scanner when you are done with input;
  • In small programs, close it at the end of main;
  • In larger programs, consider using try-with-resources;
  • Avoid creating multiple Scanner objects for System.in;
  • Only close System.in (by closing the last Scanner) when your program is truly finished reading input.
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Why is it important to close the Scanner object after use?

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