read specific line from text file

[Lesole Mphinyane]

hey all, look at my code hear;

    
   import java.io.*;
   import java.util.*;
 
    public class Main {
   
       public static void main(String[] args) throws Exception {
       
         BufferedReader br = new BufferedReader(new FileReader("users.txt"));
         String str;
         int start = 0;
      	int end = 0;
         int count = 0;
    
         while((str = br.readLine())!= null)
         {         	
            StringTokenizer st = new StringTokenizer(str," ");
            count++;
            System.out.println(st.nextToken());      
         }
         end = count;
         int num = (int)(start + (Math.random() * (end-start)));
         System.out.println(num);   
         
         br.close();
      }
   }

how do i read text file line at num,
num is the random number generated...
pliz help..

[Bear Bibeault]

Lesole Mphinyane wrote:pliz help..

Please use real words when posting to the forums. Abbreviations such as "pliz" in place of "please" only serve to make your posts more difficult to read and less likely to generate useful responses.

Please read this for more information.

thanks,
bear
JavaRanch sheriff

[Rob Camick]

You can't randomly read a line from a file (unless each line in the file is of the same length, then you can use a RandomAccesFile), you need to read every line sequentially.

So you could read each line of the file into an ArrayList. Then when you generated the random number you access the line from the ArrayList.

[Lesole Mphinyane]

thanks Bear..
@Rob, um not quite familiar with ArrayLists,
given a text file of 10 lines, how do i read line number 4..?

[Rob Camick]

Create a loop and read 4 lines.

[Lesole Mphinyane]

Rob Camick wrote:Create a loop and read 4 lines.

i mean reading the fourth line only, is it possible

[Rob Camick]

I'm not going to repeat myself, I already gave you the answer to that question!

[Lesole Mphinyane]

Rob Camick wrote:I'm not going to repeat myself, I already gave you the answer to that question!

thanks but i didn't get it clearly.

[Rob Camick]

thanks but i didn't get it clearly.

What did I say that is so confusing?

[Lesole Mphinyane]

is the anyhow i can do it without using ArrayLists?

[Bear Bibeault]

Sure. You could use an array. But that would likely be wasteful and inefficient and prone to error unless you know in advance how many lines to read.

What's your beef with ArrayLists?

[Lesole Mphinyane]

Bear Bibeault wrote:Sure. You could use an array. But that would likely be wasteful and inefficient and prone to error unless you know in advance how many lines to read.

What's your beef with ArrayLists?

its not that i have beef with ArrayLists, i cant learn them now.. will try to use the LineNumberReader. how is it

[Rob Camick]

Lesole Mphinyane wrote:
its not that i have beef with ArrayLists, i cant learn them now..

What have you been doing for the last hour. It only takes 5 minutes to learn how to use them.

Or you could continue to waste time by trying to use a LineNumberReader, which won't work either.

[Rob Spoor]

You can only read a specific line without using a List if you already know how many lines there are. If you don't you may end up trying to read a line that simply isn't there.

As for how List and ArrayList work, it's really simple. In pseudo code:

List<String> lines = new ArrayList<Line>();
while (there is another line)
{
    lines.add(that line);
}
int lineCount = lines.size();
int lineNo = (int)(Math.random() * lineCount);
String line = lines.get(lineNo);

For more information, read this.