Java compiler can't find my Scanner variable

Question

import java.io.*;
import java.util.*;

class Read
{
    public static void main(String args[])
    {
        try {
        Scanner scan = new Scanner(new java.io.File("textfile.txt"));
        } catch (FileNotFoundException e){
        }        
        while(scan.hasNext()){
        String line = scan.nextLine();
        String[] elements = line.split(",");
        }
    }
}

Why do I get

error: cannot find symbol
        while(scan.hasNext()){
              ^
  symbol:   variable scan

?

My "Votes Cast" page shows that I don't do improper things like that. — Wuschelbeutel Kartoffelhuhn
– Wuschelbeutel Kartoffelhuhn, Commented May 29, 2016 at 17:07
Fair enough. You do know the post you just replied to is 3 1/2 years old, right? — paulsm4
– paulsm4, Commented May 29, 2016 at 17:15

Makoto · Accepted Answer · 2012-12-03 03:57:30Z

4

The issue is with the scope. You can declare the Scanner object outside of the try...catch block, and instantiate it inside of it.

It's definitely also the case that you would want to put all of your I/O operations that depend on the Scanner being instantiated inside of the try...catch too, or you'll run into issues later.

Example:

public static void main(String[] args) {
    Scanner scan = null;
    try {
        scan = new Scanner(new File("textfile.txt"));
        // other I/O operations here including anything that uses scan
    } catch (FileNotFoundException e) {
        System.out.println("helpful error message", e);
    }
 }

edited Dec 3, 2012 at 3:57

answered Dec 3, 2012 at 3:50

Makoto

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3 Comments

Wuschelbeutel Kartoffelhuhn Over a year ago

Thanks I fixed it but now i get error: variable scan might not have been initialized while(scan.hasNext()){

Makoto Over a year ago

Declare and instantiate the variable to null then. Although that scares me a bit - if you move all of your I/O operations inside of the try portion of the try...catch, you shouldn't run into that issue.

Wuschelbeutel Kartoffelhuhn Over a year ago

I just followed your advice and put my code in the try block and it works now (surprisingly)

bhuang3 · Accepted Answer · 2012-12-03 03:52:06Z

0

Your scan should be declared outside the try-catch block, or you can put while loop in try-catch block

answered Dec 3, 2012 at 3:52

bhuang3

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3 Comments

Hot Licks Over a year ago

Be sure to set scan to null where you declare it, of you'll still get errors.

paulsm4 Over a year ago

Or inside the try/catch block ... along with your while loop. It doesn't make sense to scan if you got an exception, does it? So putting it inside the loop is definitely reasonable. IMHO...

bhuang3 Over a year ago

@paulsm4 Good point, thank you very much.. l learned a lot from this question though I'm not the author of it..

Chan · Accepted Answer · 2012-12-03 03:54:34Z

0

Changed the place of the where loop.

import java.io.*;
import java.util.*;

class Read
{
    public static void main(String args[])
    {
        try {
        Scanner scan = new Scanner(new java.io.File("textfile.txt"));
         while(scan.hasNext()){
          String line = scan.nextLine();
          String[] elements = line.split(",");
         }
        } catch (FileNotFoundException e){
           e.printStackTrace();
        }        
    }
}

answered Dec 3, 2012 at 3:54

Chan

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1 Comment

paulsm4 Over a year ago

your answer is absolutely correct. It looks like some idi0t came through and downvoted everybody. Probably didn't take his/her meds :) C'est la vie...

paulsm4 · Accepted Answer · 2012-12-03 03:54:58Z

-1

class Read
{
    private static final String TEXT_FILE = "textfile.txt";

    public static void main(String args[])
    {
        // BAD
        try {
          Scanner scan = new Scanner(new java.io.File("textfile.txt"));
        } 
        catch (FileNotFoundException e) {
          ; // Eating exceptions - a bad habit :(
        }        
        while(scan.hasNext()){
          String line = scan.nextLine();
          String[] elements = line.split(",");
        }
    }
}

In contrast ...

class Read
{
    public static void main(String args[])
    {
        // Good
        try {
          Scanner scan = new Scanner(new java.io.File(TEXT_FILE));
          while(scan.hasNext()){
            String line = scan.nextLine();
            String[] elements = line.split(",");
          }
        } 
          catch (FileNotFoundException e){
            System.out.println ("Error parsing " + TEXT_FILE + ": " + e.getMessage());
        }        
    }
}

answered Dec 3, 2012 at 3:54

paulsm4

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2 Comments

Makoto Over a year ago

Why do you redeclare the variable? Variable shadowing definitely takes effect here.

paulsm4 Over a year ago

@Duli-chan - I agree. In this case, declaring "Scanner scan" inside the try/catch block is best. I changed the code accordingly :)

Extreme Coders · Accepted Answer · 2012-12-03 04:14:13Z

-1

Try this code

import java.io.*;
import java.util.*;

class Read
{
public static void main(String args[])
{
    Scanner scan=null;
    try 
    {
       scan = new Scanner(new java.io.File("textfile.txt"));
       while(scan!=null)
       {
        String line = scan.nextLine();
        String[] elements = line.split(",");
       }
    } catch (FileNotFoundException e){ }        
}
}

edited Dec 3, 2012 at 4:14

answered Dec 3, 2012 at 3:53

Extreme Coders

3,5312 gold badges45 silver badges57 bronze badges

3 Comments

Makoto Over a year ago

If that file doesn't exist, your code blows up since you're dereferencing null.

Makoto Over a year ago

...no you didn't. Keep at it, you'll get it soon. :)

paulsm4 Over a year ago

Never play "whack-a-mole" with Makoto - he's too quick on the draw :)

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