String appended does not show up in System.out.println

Question

I am trying to generate a line of 10000 random number and store it in a file. I go on adding new random numbers to the line separated by spaces. But after few iterations, the appended string becomes empty(?), it doesn't show up when I try to print the line on console using System.out.println, and nothing is written into the file. The code works absolutely fine for n=10, n=100, n=1000.

Find below my code

import java.io.BufferedWriter;
import java.io.FileWriter;

public class RandomNumber {

    public static void main(String[] args) {

    try {

        int n = 10000;
        String line = ""; // Have tried StringBuilder too, doesn't help
        for (int i = 0; i < n; i++) {
            int temp = (int) Math.ceil((Math.random() * n));
            line = line+temp+" ";
            System.out.println(line);
        }
        FileWriter fstream = new FileWriter("input" + n + ".txt");
        BufferedWriter out = new BufferedWriter(fstream);
        out.write(line);
        out.close();
    } catch (Exception e) {
        System.err.println("Error: " + e.getMessage());
    }
    }
}

edit: I have removed the for loop used for out.write, it was not necessary. I had used it when I had used a String array.

Answer 1

Try this

import java.io.BufferedWriter;
import java.io.FileWriter;

public class RandomNumber {

    public static void main(String[] args) {

    try {

        int n = 10000;
        String line = "";
        for (int i = 0; i < n; i++) {
            int temp = (int) Math.ceil((Math.random() * n));
            line = line+temp+" ";
            System.out.println(line);
        }

        System.out.println("file name is :: input" + n + ".txt");
        FileWriter fstream = new FileWriter("input" + n + ".txt");
        BufferedWriter out = new BufferedWriter(fstream);
        // till here you were correct.
        // you don't need the loop here...
        out.write(line);
        out.close();
    } catch (Exception e) {
        System.err.println("Error: " + e.getMessage());
    }
    }
}

Also take a look here.

---

Edit 1

As your program is working fine with n=10, n=100, n=1000, I would suggest you to increase the heap size in Eclipse.

Answer 2

You are creating 1000 files instead of creating single file with 1000 random numbers check this. Please try to run this , it will be helpful.

try {

    int n = 10;
    String line = "";
    for (int i = 0; i < n; i++) {
        int temp = (int) Math.ceil((Math.random() * n));
        line = line+temp+" ";
        System.out.println(line);
    }
    FileWriter fstream = new FileWriter("D:/workspace/StackOverflow/src/fileread/test.txt");
    BufferedWriter out = new BufferedWriter(fstream);
              out.write(line);

    out.close();
} catch (Exception e) {
    System.err.println("Error: " + e.getMessage());
}

Console output :

4 
4 10 
4 10 7 
4 10 7 1 
4 10 7 1 4 
4 10 7 1 4 5 
4 10 7 1 4 5 1 
4 10 7 1 4 5 1 4 
4 10 7 1 4 5 1 4 8 
4 10 7 1 4 5 1 4 8 4 

test.txt-- content

4 10 7 1 4 5 1 4 8 4 

Answer 3

Never use concatenation inside loops. Use StringBuilder in this way:

import java.io.BufferedWriter;
import java.io.FileWriter;

public class RandomNumber {

    public static void main(String[] args) {

    try {

        int n = 10000;
        StringBuilder sb = new StringBuilder();
        for (int i = 0; i < n; i++) {
            int temp = (int) Math.ceil((Math.random() * n));
            sb.append(temp).append(" ");
        }
        FileWriter fstream = new FileWriter("input" + n + ".txt");
        BufferedWriter out = new BufferedWriter(fstream);
        out.write(sb.toString());
        out.close();
    } catch (Exception e) {
        System.err.println("Error: " + e.getMessage());
    }
    }
}

Answer 4

if you just want one really long line you should write in the loop, not storing it in a variable.

i think the problem is that the string just gets so long (i got a file with 48kb with code below) that it gets out of memory. though strange that it doesnt throw an OutOfMemoryException or similar.

public static void main(String[] args) {

    try {

        int n = 10000;
        FileWriter fstream = new FileWriter("input" + n + ".txt");
        BufferedWriter out = new BufferedWriter(fstream);

        for (int i = 0; i < n; i++) {
            int temp = (int) Math.ceil((Math.random() * n));
            out.write(temp+" ");
            out.flush();
        }
        out.close();
    } catch (Exception e) {
        System.err.println("Error: " + e.getMessage());
    }
}