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Writing to a file

Posted on 2004-04-10
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Last Modified: 2010-03-31
I need to read in a file, and then create a file which includes the first file content.  For example i read file A which contains

abc
def

then i need to read in, and then create a file which has the format:

1: abc
2: def

any idea?
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Question by:jtcy
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10 Comments
 
LVL 92

Expert Comment

by:objects
ID: 10796070
BufferedReader in = new BufferedReader(new FileReader("in.txt"));
PrintWriter out = new PrintWriter(new FileReader("out.txt"));
String line = null;
int lineno = 1;
while (null!=(line=in.readLine()))
{
   out.println(lineno+": "+line);
   lineno++;
}
in.close();
out.close();

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Author Comment

by:jtcy
ID: 10796272
I have this method in class Parser,

public void writeFile(FileReader in) throws java.io.IOException
    {
          FileWriter writer = new FileWriter("LISTING.txt");
          PrintWriter out = new PrintWriter(writer);
          
          BufferedReader inFile = new BufferedReader(in);
          String line = inFile.readLine();
          
          int j = 1;
          while (line != null)
           {
                 System.out.println(line);
                 out.println(j+ " :" + line);
                 j++;
           }
          
          inFile.close();
            out.close();

    }

then in driver class, i do:

parser.writeFile(inFile);

the Listing file did create but is still blank~ :~(
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Accepted Solution

by:
objects earned 500 total points
ID: 10796285
that won't work cause you don't read the next line in your loop.

should be more like:

public void writeFile(FileReader in) throws java.io.IOException
    {
         FileWriter writer = new FileWriter("LISTING.txt");
         PrintWriter out = new PrintWriter(writer);
         
         BufferedReader inFile = new BufferedReader(in);
         String line =null;
         
         int j = 1;
         while ((line = inFile.readLine())!= null)
          {
               System.out.println(line);
               out.println(j+ " :" + line);
               j++;
          }
         
         inFile.close();
          out.close();

    }
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Author Comment

by:jtcy
ID: 10796296
I changed it, still doesnt work. 0kb file produced~
0
 

Author Comment

by:jtcy
ID: 10796305
FileWriter writer = new FileWriter("LISTING.txt");
          PrintWriter out = new PrintWriter(writer);
          
          BufferedReader inFile = new BufferedReader(in);
          String line = null;
        System.out.println(inFile.readLine()); // I do a test here

and it seems like the file read in is null. how can that be. i am very sure the file is not null. Could it be perhaps we cant pass Filereader object as parameter?
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LVL 92

Expert Comment

by:objects
ID: 10796308
SOunds like either the file you are reading is empty, or you have already read all it's contents.
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LVL 92

Expert Comment

by:objects
ID: 10796313
Make sure you haven't already been reading from the FileReader you are passing in.
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Author Comment

by:jtcy
ID: 10796325
>> Make sure you haven't already been reading from the FileReader you are passing in.


cool. solved it.
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LVL 92

Expert Comment

by:objects
ID: 10796344
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Author Comment

by:jtcy
ID: 10796346
hey, u're my senior LOL
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