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    <p>Your code is <strong>very</strong> inefficient. You re-read the file second time on every line(!!!) in the file. Disk IO is very slow.</p> <p>What you should do is to load the file into a parsed memory structure (an array of doubles), and then do a nested loop over it.</p> <blockquote> <p>Am I correct in thinking my code is not able to be multithreaded?</p> </blockquote> <p>You're incorrect. This task would benefit a lot from threading. But your first priority is to get rid of repetitive IO. I'd guess the performance would be good enough then. </p> <p><strong>UPDATE</strong> to <strong>UPDATE</strong></p> <p>Rewrote your class to multiple threads (4 by default). Downside: lines in the output file are not written in order, though by using unix sort utility you may sort it after the computation, if needed. Both A->B and B->A are still calculated as I couldn't come up with a simple way to store the result of A->B short of using Java 64bit and installing some 64G of RAM.</p> <pre><code>import java.io.BufferedWriter; import java.io.File; import java.io.FileWriter; import java.io.IOException; import java.io.PrintWriter; import java.io.Writer; import java.util.ArrayList; import java.util.List; import java.util.Scanner; public class Coord { public int a, b, c, d, e, f; private static class CoordsThread extends Thread { private int start; private int end; private List&lt;Coord&gt; coords; private PrintWriter out; public CoordsThread(int start, int end, List&lt;Coord&gt; list, PrintWriter out) { this.start = start; this.end = end; this.coords = list; this.out = out; // last block can be shorter if( this.end &gt; this.coords.size() ) this.end = this.coords.size(); } public void run() { System.out.println("started thread "+getName()+" for ["+start+";"+end+")"); for (int i = start; i &lt; end; i++) { for (int j = 0; j &lt; coords.size(); j++ ) { Coord c1 = coords.get(i); Coord c2 = coords.get(j); double foo = ((c1.a - c2.a) * (c1.a - c2.a)) * 1; double goo = ((c1.b - c2.b) * (c1.b - c2.b)) * 1; double hoo = ((c1.c - c2.c) * (c1.c - c2.c)) * 2; double joo = ((c1.d - c2.d) * (c1.d - c2.d)) * 2; double koo = ((c1.e - c2.e) * (c1.e - c2.e)) * 4; double loo = ((c1.f - c2.f) * (c1.f - c2.f)) * 4; double zoo = Math.sqrt(foo + goo + hoo + joo + koo + loo); synchronized (out) { out.println(i*coords.size()+j + "; " + i + " " + j + " " + zoo); } } } System.out.println("completed thread "+getName()); } } public static void main(String[] args) throws Exception { PrintWriter out = new PrintWriter(new BufferedWriter(new FileWriter("2.txt"))); Scanner sc = new Scanner(new File("1.txt")); List&lt;Coord&gt; coords = new ArrayList&lt;Coord&gt;(); // for each line in the file while (sc.hasNextLine()) { String[] numstrs = sc.nextLine().split("\\s+"); Coord c = new Coord(); c.a = Integer.parseInt(numstrs[1]); c.b = Integer.parseInt(numstrs[2]); c.c = Integer.parseInt(numstrs[3]); c.d = Integer.parseInt(numstrs[4]); c.e = Integer.parseInt(numstrs[5]); c.f = Integer.parseInt(numstrs[6]); coords.add(c); } System.out.println("total lines read: "+coords.size()); int threadsCount = 4; List&lt;Thread&gt; ths = new ArrayList&lt;Thread&gt;(); int blockSize = coords.size()/threadsCount+1; for( int i=0; i&lt;threadsCount; ++i ) { CoordsThread ct = new CoordsThread(i*blockSize, (i+1)*blockSize, coords, out); ct.setName("Block"+i); ths.add(ct); } for (Thread th : ths) { th.start(); } for (Thread th : ths) { th.join(); } out.flush(); out.close(); } } </code></pre>
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    1. USVladimir Dyuzhev
    1. USVladimir Dyuzhev
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    1. COWhen the whole file residents in memory you can just double for loop over them and output it.
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      1. USThomas Jungblut
    2. COyamburg, I'm pretty new to arrays, can you perhaps point me in a good for dealing with text files in terms of array, retrieving information stored in array. Either way, your response in insightful, thanks
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      1. USevanlivingston
    3. COadded some pseudocode for you. should be enough.
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      1. USVladimir Dyuzhev
 

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