Performance Testing

On my spare time I have been doing some Performance Testing mechanisms in Java.
I just wrote a small code snippet and ran it in a Worker thread and tried to improve
the performance of it. Even though this is small the lesson I learned was immense.

This is the worker class I used.

import java.util.concurrent.*;



public class Callee implements Callable<Integer> {

    public Integer call() {

        int i = 0;

        while(i < 10000) {

            System.out.println(i);            

            i++;

        }

        return i;

    }

}

And the worker was called by the following class

import java.util.concurrent.*;

import java.awt.*;



public class Caller {

    public static void main(String[] args)throws Exception {

        long startFreeMemory = Runtime.getRuntime().freeMemory();

        long startTime = System.currentTimeMillis();

        ExecutorService exec = Executors.newCachedThreadPool();

        Future<Integer> f = exec.submit(new Callee());

        exec.shutdown();

        System.out.println("Future is "+f.get());

        long endTime = System.currentTimeMillis();

        long endFreeMemory = Runtime.getRuntime().freeMemory();

        System.out.println("Memory used : "+(startFreeMemory - endFreeMemory));

        System.out.println("Duration : "+(endTime - startTime));

    }

}

Testing was done in Intel Core 2 Duo Process with 2.93 GHz and 2 Gb of RAM.

The initial program ran for 672 Milliseconds and Used 674408 units of RAM.

Then the Callee class was changed to the following.

import java.util.concurrent.*;



public class Callee implements Callable<Integer> {

    public Integer call() {

        int i = 0;

        StringBuilder sb = new StringBuilder();

        while(i < 10000) {        

            sb.append(i+"\n");

            i++;

        }

        System.out.print(sb.toString());

        return i;

    }

}

Using a StringBuffer without directly printing to the screen reduced the execution time by 188 Milliseconds but the RAM units used increased to 828288.

But just changing

sb.append(i+"\n");

to

sb.append(i).append("\n");

reduced the RAM Usage by almost half from the previous implementation.