How to close a Scanner object inside a try loop without closing System.in?

Question

 public static int take1(){
      Scanner in = new Scanner(System.in);
      while(true){
          try{
              System.out.print("\nHow many coloms you want = ");
              return in.nextInt();
          }
          catch(Exception e ){
              System.out.println("Sorry,Please enter only no.");
              in.next();
          } 
      }  
  }

how to close the scanner object , if i close this object using finally or try with resources it also closes System.in , and i cant read from stream more than once. what is the best method to do this?

Why do you want to close it? Is it just because there is a compiler warning? — Codebender, Jul 14 '15 at 09:36
possible duplicate of [Close Scanner without closing System.in](http://stackoverflow.com/questions/14962082/close-scanner-without-closing-system-in) — mhlz, Jul 14 '15 at 09:52
If you are looking to call your method `take1` multiple times, don't create scanner object in this method. Create it where you are calling the `take1()` method and pass the scanner object as argument to your method, like `take1(Scanner sc)`, then close the scanner in your main method once you are done calling your method multiple times. — Amit.rk3, Jul 14 '15 at 09:59
Thanks @Amit.rk3 , your approach worked for me , atleast now i dont see that compiler warning. — mightyWOZ, Jul 14 '15 at 10:23

score 1 · Answer 1 · edited Oct 23 '17 at 18:21

1

You should use this:

finally {       
    sc.reset();
}

rather than sc.close();

edited Oct 23 '17 at 18:21

Shiladittya Chakraborty

4,270
8
45
94

answered Oct 23 '17 at 16:58

user8820699

11
1

Rustam · Answer 2 · 2015-07-14T10:10:35.577

put finally block and close the open resource.

Java finally block is a block that is used to execute important code such as closing connection, stream etc.

Java finally block is always executed whether exception is handled or not.

 try
  {
      System.out.print("\nHow many coloms you want = ");
      return in.nextInt();
  } catch(Exception e ){
            System.out.println("Sorry,Please enter only no.");
            in.next();
   }finally{
            in.close();
   }

EDITED AS PER Naman Gala

check if exception occured then don't close it let it go for next loop util no. is entered otherwise close it.

public static int take1()
    {
        boolean isExceptionOccured=false;
        Scanner in = new Scanner(System.in);
        while(true)
        {
            try
            {
                System.out.print("\nHow many coloms you want = ");
                isExceptionOccured=false;
                return in.nextInt();
            }
            catch(Exception e )
            {
                isExceptionOccured=true;
                System.out.println("Sorry,Please enter only no.");
                in.next();
            }finally{
                if(!isExceptionOccured){
                in.close();
                System.out.println("resource closed");
                }
            }

        }

    }

Lets consider an exception occur then what will be the behavior of the program? — Naman Gala, Jul 14 '15 at 10:02
yes you are right @NamanGala check the edited. thanks for pointing out. — Rustam, Jul 14 '15 at 10:07
finally can not be used , because it will close the object (and also the System.in) in first iteration , which means it will throw an exception after first iteration. — mightyWOZ, Jul 14 '15 at 10:09

score -3 · Answer 3 · answered Jul 14 '15 at 09:45

-3

Use a variable inside try and then close. For example,

 public static int take1()
  {
      Scanner in = new Scanner(System.in);
      while(true)
      {
          try
          {
              System.out.print("\nHow many coloms you want = ");
              int i =  in.nextInt();
              in.close();
              return i;
          }
          catch(Exception e )
          {
              System.out.println("Sorry,Please enter only no.");
              in.next();
          }

      }

  }

This approach help you to close the object avoiding finally block.

answered Jul 14 '15 at 09:45

Mohammad Mosiur

59
1
8

1

This is bad. If there's an exception at `int i = in.nextInt();` or at `in.next():` the resource will never get closed. – mhlz Jul 14 '15 at 09:51
Test the code and then give down vote after proper understanding. Here if any exception occurs it will again asks the input. The program will not terminated unless a valid input is given. – Mohammad Mosiur Jul 14 '15 at 09:53
1

Not if there's an exception at `in.next();` like I said in my comment. – mhlz Jul 14 '15 at 09:55
Sorry , but i have tested it already and this approach does not work. the problem is not how you close the object , but once the object is closed it also closes System.in , which means if iterate for more than once ,it will throw an exception since we can not read from the closed input stream. – mightyWOZ Jul 14 '15 at 10:15

How to close a Scanner object inside a try loop without closing System.in?

3 Answers3