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Java error with variable initialization

  1. Oct 19, 2013 #1
    Code (Text):
    import java.util.Scanner;
    import java.io.FileNotFoundException;
    import java.io.FileReader;
    import java.io.IOException;
    import java.io.PrintWriter;

    public class CountryPopulationReverse{

       public static void main(String args[])throws FileNotFoundException {
       
       //Variable declarations
          Scanner in = new Scanner(System.in);
          Scanner FileIn;
          FileReader inputFile;
          String population, country;
          int checkNum;
          PrintWriter output;
          boolean good = true;
         
         
          try
          {
          System.out.print("Input file: ");
          String inputName = in.nextLine();
          inputFile = new FileReader(inputName);
          FileIn = new Scanner(inputFile);
          System.out.print("Output file: ");
          String outputName = in.nextLine();
          output = new PrintWriter(outputName);
          }catch(FileNotFoundException e){ System.out.println("File not found.");}
         
         while(good)
         {
          try
          {
          /*
          System.out.print("Input file: ");
          String inputName = in.nextLine();
          inputFile = new FileReader(inputName);
          FileIn = new Scanner(inputFile);
          System.out.print("Output file: ");
          String outputName = in.nextLine();
          output = new PrintWriter(outputName);
          */
         
         
                while(FileIn.hasNextLine())
                {
                   while(!FileIn.hasNextInt())
                   {
                        country = FileIn.next();
                        output.print(country);    
                   }
                   
                   population = FileIn.next();
                 
                   checkNum = Integer.parseInt(population);
                   output.println(checkNum);
                   System.out.println(checkNum);
                   if(checkNum<=5)
                       throw new BadDataException("Population (" + checkNum + ") is too low.");
                   if(checkNum>2000000000)
                      throw new BadDataException("Population (" + checkNum + ") is too high.");
                     
                }
               output.close();
               good=false;
         
          } catch (FileNotFoundException e){ System.out.println("File not found.");}
            catch (BadDataException e) { System.out.println("Bad Data: " + e.getMessage());}
            catch (NumberFormatException e) { System.out.println("Number Format Exception found.");}
           
         }//End while loop
         
       }
    }
    Code (Text):
    CountryPopulationReverse.java:46: error: variable FileIn might not have been initialized
                while(FileIn.hasNextLine())
    Not understanding java right now Why cant I declare these variables outside the try block?!!?!? I hate java I would rather do C it is so much more lenient.

    Only time this program compiles is when I remove the innner comments of the try block and delete the top portion.
     
  2. jcsd
  3. Oct 20, 2013 #2
    Lenient isn't always good. The compiler complaints usually are there for a reason. For example, the compiler is quite right here. If that Scanner(File) call throws FileNotFoundException in the first try/catch block, you just print something in the catch part. Now, between those 2 try/catch blocks, the FileIn variable could in fact be not initialized.

    And it's with that that you enter the second try/catch block. You didn't really handle the error in a good way, here. I'm going to side with the compiler on this one, I'm afraid. :)

    BTW, the indentation doesn't really help make it easy to read. Good formatting and clarity are some of the key aspects of good code.
     
    Last edited: Oct 20, 2013
  4. Oct 20, 2013 #3
    If by "lenient" you mean it doesn't complain, when you put a bug in your code that could cause all kinds of undefined behaviour.
    I'm not entirely shure what your code is supposed to do but I'm guessing it should look more like this.

    Code (Text):
    public class CountryPopulationReverse {

        public static void main(String args[]) {
            Scanner in = new Scanner(System.in);
            Scanner FileIn = null;
            PrintWriter output = null;

            try
            {
                System.out.print("Input file: ");
                String inputName = in.nextLine();
                FileReader inputFile = new FileReader(inputName);
                FileIn = new Scanner(inputFile);
                System.out.print("Output file: ");
                String outputName = in.nextLine();
                output = new PrintWriter(outputName);
                while(FileIn.hasNextLine())
                {
                   while(!FileIn.hasNextInt())
                   {
                        String country = FileIn.next();
                        output.print(country);    
                   }
                   
                   String population = FileIn.next();
                 
                   int checkNum = Integer.parseInt(population);
                   output.println(checkNum);
                   System.out.println(checkNum);
                   if(checkNum<=5)
                       throw new BadDataException("Population (" + checkNum + ") is too low.");
                   if(checkNum>2000000000)
                      throw new BadDataException("Population (" + checkNum + ") is too high.");
                     
                }
            } catch(FileNotFoundException e){ System.out.println("File not found.");}
              catch (BadDataException e) { System.out.println("Bad Data: " + e.getMessage());}
              catch (NumberFormatException e) { System.out.println("Number Format Exception found.");}
              finally {
                if(output != null) {
                    output.flush();
                    output.close();
                }
                if(FileIn != null) FileIn.close();
              }
        }
    }
     
  5. Oct 30, 2013 #4

    harborsparrow

    User Avatar
    Gold Member

    You can probably squelsh that error like this:

    Scanner FileIn = null;

    It's really warning you about something important, though. I see you are trying to do something with FileIn in your catch statement, and since the initialization of FileIn is in the try block, the catch block will not see that it has been initialized. Sure enough, it will be null, but you seem to assume it might not be at that point, and that is what the compiler is really upset about.

    It is generally worthwhile to put a try-catch structure around every library call (such as initialization of a Scanner), because that specific initialization can fail. Having the try catch just for that part allows you the option to tailor an error message (or set a condition flag) for that specific failure.
     
    Last edited: Oct 30, 2013
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