Scanner close after use

问题:

While using scanner like following:

Scanner s = new Scanner(System.in);
String response = s.next();

Boolean approved = (response.contains("Y") || response.contains("y")) ? true : false;

if (approved){
  Do Stuff      
}
s.close();

I'm getting no such Element exception exception:

Exception in thread "main" java.util.NoSuchElementException at java.util.Scanner.throwFor(Unknown Source) at java.util.Scanner.next(Unknown Source)****

I'm calling s (Scanner) multiple times, the runtime error occur on the second call. This is due to closing the scanner and than probably using it again. My question is, I'm creating a new instance of Scanner every time I'm using it so why I'm getting the runTime error?

回答1:

The problem is

When a Scanner is closed, it will close its input source if the source implements the Closeable interface.

http://docs.oracle.com/javase/1.5.0/docs/api/java/util/Scanner.html

Thus scan.close() closes System.in.

To fix it you can make

Scanner scan static or pass every time scanner object in method and close it at last.

回答2:

I think because you are not deleting the scanner. Try to delete the instance of s before calling it again. And if memory isn't a constraint you could always make a new scanner object, but it's better coding practice to properly de-allocate memory when you are done.