Stream closed and not reopened - Java

Question

I have an easy 'homework' to do, but I have found a little problem with the closure of the input stream. To put it simply, I have to make a contact 'list' application in Java, just to use the polymorphism in the correct way. So I have a class Contact and a subclass Private (contact). In both class there is a modify method to change the value of the variables.

public void modify() throws IOException {
    System.out.println("Previously name: " + name);
    System.out.println("Insert new name");
    try(InputStreamReader ir = new InputStreamReader(System.in);    
    BufferedReader in = new BufferedReader(ir) ) {  
        name= in.readLine();
        System.out.println("You've changed the name to: "+ name);                       
    System.out.println("Previously surname: " + surname);
    System.out.println("Insert new surname");
        surname= in.readLine();
        System.out.println("You've changed the surname to: "+ surname);                         
    System.out.println("Previously e-mail: " + email);
    System.out.println("Insert new e-mail");
        email = in.readLine();
        System.out.println("You've changed the e-mail to: "+ email);    }                   
}

This is the Contact method that doesn't create problem

@Override 
public void modify() throws IOException {
    super.modifica();
    System.out.println("Numero di cellulare precedente: " + cell);
    System.out.println("Inserire nuovo numero");
    try (InputStreamReader ir = new InputStreamReader(System.in);   
    BufferedReader in = new BufferedReader(ir)) {
        cell = in.readLine();
        System.out.println("Hai cambiato il numero in: "+ cell);                        
    System.out.println("Contatto skype precedente: " + skype);
    System.out.println("Inserire nuovo contatto");
        skype = in.readLine();
        System.out.println("Hai cambiato il contatto in: "+ skype);                         
}   
}

Instead, this is the override of the method in Private. In the main, I create a Private object and I call the modify method. I can insert name, surname and e-mail without problem, then the method throws an IO exception because the stream is closed. I can't understand why I have this kind of problem. I think that the stream is closed by try with resources in the first code, but then it is opened in the second code by another try with resources. Probably something in my idea is wrong.

Maybe you should learn about `java.util.Scanner`. You could start here: http://stackoverflow.com/a/11871792/4791599 — Markus Mitterauer, Aug 07 '16 at 01:26
Thank you! Are there differences in terms of potentiality and administration of memory between Scanner and BufferedReader? — Bondye, Aug 10 '16 at 12:26
Possible duplicate of [Closing BufferedReader and System.in](http://stackoverflow.com/questions/8203981/closing-bufferedreader-and-system-in) — Markus Mitterauer, Aug 12 '16 at 15:18

Nicolas Filotto · Accepted Answer · 2016-08-06T19:17:29.320

0

Your problem is indeed due to the try-with-resource statement that closes new InputStreamReader(System.in) which behind the scene closes also the underlying input stream that is System.in (in is a public static field of System) such that in your modify method System.in is already closed and then cannot be read anymore this is why you get this exception.

edited Aug 06 '16 at 19:17

answered Aug 06 '16 at 18:56

Nicolas Filotto

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... and the Stream `System.in` cannot be *reopened* by an application. – Markus Mitterauer Aug 06 '16 at 19:14
Do I need to delete try? Because I read in a book it's important to close the stream as soon as possible and the autor suggests to use try with resource to do it. – Bondye Aug 06 '16 at 19:33
using try-with-resources statement is indeed a good practice but not here as the only resouce that you really close must not be closed so you can't use it here – Nicolas Filotto Aug 07 '16 at 08:46
What can I do to avoid any waste of memory in this situation? – Bondye Aug 07 '16 at 09:58
let the GC do its job – Nicolas Filotto Aug 07 '16 at 11:19
Thank you! Lesson n. 1: close() and try with resources are not necessary to release the memory used by the stream. – Bondye Aug 10 '16 at 12:19
once again this is a very specific use case most of the time using try-with-resource statement is the right approach. – Nicolas Filotto Aug 10 '16 at 12:44
If my answer is good enough, don't hesitate to up vote two, thx in advance – Nicolas Filotto Aug 10 '16 at 12:45

score 0 · Answer 2 · edited May 23 '17 at 10:28

You could still use try-with-resources if you wrap System.in with a CloseShieldInputStream.

I would also recommend using a Scanner instead of the InputStreamReader and BufferedReader, because of it's simplicity:

import java.util.Scanner;
import org.apache.commons.io.input.CloseShieldInputStream;

public class Contact {

    protected String name;
    protected String surname;
    protected String email;

    public void modify() throws IOException {
        System.out.println("Previously name: " + name);
        System.out.println("Insert new name");
        try (Scanner sc = new Scanner(new CloseShieldInputStream(System.in))) {
            name = sc.nextLine();
            System.out.println("You've changed the name to: " + name);
            System.out.println("Previously surname: " + surname);
            System.out.println("Insert new surname");
            surname = sc.nextLine();
            System.out.println("You've changed the surname to: " + surname);
            System.out.println("Previously e-mail: " + email);
            System.out.println("Insert new e-mail");
            email = sc.nextLine();
            System.out.println("You've changed the e-mail to: " + email);
        }
    }
}

public class Private extends Contact {

    private String cell;
    private String skype;

    @Override
    public void modify() throws IOException {
        super.modify();
        System.out.println("Numero di cellulare precedente: " + cell);
        System.out.println("Inserire nuovo numero");
        try (Scanner sc = new Scanner(new CloseShieldInputStream(System.in))) {
            cell = sc.nextLine();
            System.out.println("Hai cambiato il numero in: " + cell);
            System.out.println("Contatto skype precedente: " + skype);
            System.out.println("Inserire nuovo contatto");
            skype = sc.nextLine();
            System.out.println("Hai cambiato il contatto in: " + skype);
        }
    }
}

See also: Closing BufferedReader and System.in

Stream closed and not reopened - Java

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