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How to read from a file ?

Posted on 2004-04-04
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Last Modified: 2010-03-31
Could you please give me the source code for a program that reads data from a file.

Example - My data.txt contains this:

1     2     3     4     5
 
Now: I want to read each number, knowing that there is a white space in between each os them. Later on the program should print in the screen:
1
2
3
4
5

Can you please code this for me and post it ?

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Question by:digi_mind
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9 Comments
 
LVL 14

Expert Comment

by:Tommy Braas
ID: 10751268
You need a BufferedReader to read the line of numbers. Then you need a StringTokenizer to split the numbers up into substrings. And finally, if you need the actual values of the numbers, they need to be parsed using the Integer class. School assignment?
0
 

Author Comment

by:digi_mind
ID: 10751293
Yes, actually is a program that I have to make for school, but the main topic is not java, but c++.

Can you code it for me ?
0
 
LVL 30

Expert Comment

by:GrandSchtroumpf
ID: 10751316
if it's for school we cannot provide you with code.
post the code you have written so far and we can guide you.
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Author Comment

by:digi_mind
ID: 10751386
This is what I have:
******************
import java.io.BufferedReader;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.FileReader;
import java.io.PrintWriter;
import java.util.Random;
import java.util.StringTokenizer;

public class WriteText {
    /**     * Constructor for WriteText.     */    
   public WriteText() {        
      super();    
   }    
   
   public static void main(String[] args) {            
     
      String SEP = " ";      
      String FILENAME = "data.txt";                
     
      try {                                  
       StringTokenizer st = null;                  
       BufferedReader reader = new BufferedReader(new FileReader(FILENAME));                  
       String s = null;                  
       String[][] myArray = new String[1][6];                  
       int col;                  
       int row;                  
       String element = null;            
      
       while ((s = reader.readLine()) != null ) {                  
          st = new StringTokenizer(s,SEP);                  
            element = st;          
       }            
       System.out.println("VALUE : " + element );    
       reader.close();      
      }catch(Exception fe) {                  
         fe.printStackTrace(System.out);            
      }    
   }
}
**********************************************
My data.txt file contains 7 strings:
one two three four five six seven

I would like to have this strings in an array, then print in the screen position 4 of the array, so I will print:

four

Give me a hand, I am almost there...

0
 

Author Comment

by:digi_mind
ID: 10751403
My new code and better:
************************
import java.io.BufferedReader;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.FileReader;
import java.io.PrintWriter;
import java.util.Random;
import java.util.StringTokenizer;

public class WriteText {
    /**     * Constructor for WriteText.     */    
   public WriteText() {        
      super();    
   }    
   
   public static void main(String[] args) {            
     
      String SEP = " ";      
      String FILENAME = "data.txt";                
     
      try {                                
      
       StringTokenizer st = null;                  
       BufferedReader reader = new BufferedReader(new FileReader(FILENAME));                  
       String s = null;                  
       String[] myArray = new String[3];                  
       int col = 0;                  
       String element = null;            
      
       while ((s = reader.readLine()) != null ) {                  
          st = new StringTokenizer(s,SEP);                  
            element = (String) st.nextElement();
          myArray[col] = element;
          col = col + 1 ;          
       }            
       System.out.println("VALUE : " + myArray[0] );    
       reader.close();      
      }catch(Exception fe) {                  
         fe.printStackTrace(System.out);            
      }  
   }
}
**************************************************

The problem is that when I print myArray[1] I get a value of null... and when I print myArray[0] I get "one" so the first value works...

i need to be able to store the other values in my array .

How ?
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LVL 30

Accepted Solution

by:
GrandSchtroumpf earned 55 total points
ID: 10751435
>      while ((s = reader.readLine()) != null ) {                  
>         st = new StringTokenizer(s,SEP);                  
>            element = st;          
>      }            

here, you read each line of the file
and create a new StringTokenizer for each line.
what you probably want to do is to read the first line only.
or maybe read each line and test if the line is empty.  if the line is not empty, you create your StringTokenizer, otherwise you read the next line.
Once you have created your StringTokenizer, you should loop on the "Enumeration" (StringTokenizer implements Enumeration) and copy the values into your Array.

another method you could use is the split() method of String that returns a String[], but it might be a little complicated because it uses regular expressions.  continue with StringTokenizer for now.
0
 
LVL 30

Expert Comment

by:GrandSchtroumpf
ID: 10751443
you need to loop on your enumeration (while loop):
use  <  st.hasMoreElements();  >  to test if you have more elements.
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