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basic file i/o

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Join Date: May 2006

Posts: 17

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jaden403

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basic file i/o

Oct 14th, 2006

I have a basic Java file I/O question. I am trying to read/write from/to a text file (obviously) from within a function that is called by main(). Can you do the following within a function:

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Scanner inFile = new Scanner(new FileReader("File1.txt"));
PrintWriter outFile = new PrintWriter("File2.txt");
 
Scanner inFile = new Scanner(new FileReader("File1.txt"));
PrintWriter outFile = new PrintWriter("File2.txt");

or does this have to be done within main()? If within main(), then how do you get inFile and outFile to work in the function? Do you pass them like a normal parameter?

I tried creating the inFile and outFile objects within a function, but kept getting errors when the program compiled. Thanks...

Jaden403

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Join Date: Feb 2006

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masijade

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Nearly a Posting Maven

Re: basic file i/o

Oct 15th, 2006

Yes, of course you can. What are the errors you are getting?

Java Programmer and Sun Systems Administrator

----------------------------------------------

Debugging is twice as hard as writing the code in the first place. Therefore, if you write the code as cleverly as possible, you are, by definition, not smart enough to debug it.
--Brian Kernighan

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Join Date: May 2006

Posts: 17

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jaden403

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Re: basic file i/o

Oct 15th, 2006

The first example works fine:

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import java.io.*;
import java.util.*;
public class File
{   
   public static void main(String[] args) throws FileNotFoundException 
   { 
     PrintWriter outFile = new PrintWriter(new PrintWriter("outputdocument.txt"));
 
   for (int i = 1; i <= 10; i++)
     outFile.printf("%d%n", i);
 
   outFile.close();
   }
}
import java.io.*;
import java.util.*;
public class File
{   
   public static void main(String[] args) throws FileNotFoundException 
   { 
     PrintWriter outFile = new PrintWriter(new PrintWriter("outputdocument.txt"));
 
   for (int i = 1; i <= 10; i++)
     outFile.printf("%d%n", i);
 
   outFile.close();
   }
}

However, when I try to do the same thing in a function:

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import java.io.*;
import java.util.*;
public class File2
{   
   public static void main(String[] args) 
   { 
       printFunction();
   }
 
  public static void printFunction() throws FileNotFoundException 
  {
     PrintWriter outFile = new PrintWriter(new PrintWriter("outputdocument.txt"));
 
    for (int i = 1; i <= 10; i++)
      outFile.printf("%d%n", i);
 
    outFile.close(); 
  }
}
import java.io.*;
import java.util.*;
public class File2
{   
   public static void main(String[] args) 
   { 
       printFunction();
   }
 
  public static void printFunction() throws FileNotFoundException 
  {
     PrintWriter outFile = new PrintWriter(new PrintWriter("outputdocument.txt"));
 
    for (int i = 1; i <= 10; i++)
      outFile.printf("%d%n", i);
 
    outFile.close(); 
  }
}

I get this message:
File2.java:14: unreported exception java.io.FileNotFoundException; must be caught or declared to be thrown
PrintWriter outFile = new PrintWriter(new PrintWriter("outputdocument.txt"));
^
1 error

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Join Date: Feb 2006

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masijade

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Nearly a Posting Maven

Re: basic file i/o

Oct 16th, 2006

Well, the error says it all.

Your method delares that it throws an exception. That means, that you must either call the method from within a try catch block, or the method (this time main) calling your method, must also declare that it throws the same exception that your method does.