Handling Resource Leaks with Scanner and System.in in Java

If you’ve worked with Java’s Scanner, you know it’s important to close it to avoid resource leaks—especially when reading from files. But when it comes to System.in, it's different.

Should You Close System.in?

You generally don’t want to close System.in because doing so will stop any future input. This can create issues if other parts of your program still need user input.

The Safe Solution: try-with-resources

Java’s try-with-resources makes it easy. It automatically closes the Scanner without closing System.in, allowing you to safely read user input.

Why Do IDEs Warn About Resource Leaks?

Some IDEs (like Eclipse or IntelliJ) might flag a potential resource leak with Scanner, treating all instances the same. This can be misleading, especially when using System.in, but you can confidently ignore these warnings.

Best Practices:

Use try-with-resources to ensure the Scanner is closed properly while keeping System.in open.
Avoid manually closing System.in; let the JVM handle it.

Example Code:

try (Scanner objName = new Scanner(System.in)) {
    System.out.println("What's your name?");
    String userName = objName.nextLine();

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