Why does it display the error: "Resource leak: 'keyboard' is never closed"?

Question

I recently installed Eclipse on a new computer and when I tried to write this code it gave me this error. I swear that I've written this type of

Scanner keyboard = new Scanner(System.in)

many of times in my old computer and have never gotten this error until now.

import java.util.Scanner;
public class W1M1 {

public static void main(String[] args) {
    System.out.println("Hellow World");
    Scanner keyboard = new Scanner(System.in); //'keyboard' word shows this error
    System.out.println("Please enter your name: ");
    String userInput = keyboard.nextLine();
    System.out.println("Hello there, " + userInput + ".");
}

}

It's not an error, it's a warning. This warning, in this specific context (that it's a scanner reading from `System.in`), can be ignored. — Andy Turner, Jun 14 '18 at 05:45
You’ve opened a `Scanner`, but never explicitly closed it. Add `keyboard.close()`, or better, use try-with-resources to automatically close it. — AJNeufeld, Jun 14 '18 at 05:47

score 0 · Answer 1 · answered Jun 14 '18 at 05:50

The Scanner class implements the Closable interface - i.e., it opens a resource, and you should call the close() method yourself, so, generally speaking, Eclipse does the right thing and produces a warning here.

However, in this specific case, keyboard is a Scanner that refers to System.in - the standard input descriptor. You should never close this yourself, and should just suppress Eclipse's warning in this case.

Why does it display the error: "Resource leak: 'keyboard' is never closed"?

1 Answers1