May 31, 2013

How to(Steps)Getting Started in Cloud: Amazon EC2


1) Create an account on, you will need a credit card to enter but you won't be charged that's for security purposes.
2) Hover your mouse over My Account / Console, click AWS Management Console. This will take you to
3) Click on EC2, This will take you to
4) On the left pane of the screen click on Key Pairs. Click Create Key Pair. Enter a name for your key click create. Your key -pair will be created and your private key will start downloading. Save it at a  safe place.
5) Get back to EC2 Console   Click on Launch Instance, this will take you to  
6) Quick Launch Wizard > Choose a Launch Configuration, scroll down

May 20, 2013

Make Java Memory Efficient

1. in getting substrings from a BIG string make a new string like here:
String mySubstring = new String(orig.split(";")[i]); 
OR new String(offset + beginIndex, endIndex - beginIndex, value);
Taken from here and here.

If you don't mind sacrificing a little accuracy vs more memory efficeiency use bloomfilter instead of hashmap.
Taken from here and here.

Use efficient designs: stuff like Flyweight Pattern! مگس وزن
use as many abstractions as you can, don't worry about it, it would pay off

I didn't know there is a method called intern for String! Note that

May 19, 2013

How to master your tmux like a BOSS! Generate tmux panes

Here is a killer point! Whatever you do with your tmux call  

$ tmux source-file .tmux.conf   

So I was monitoring several processes on a server from my laptop and whenever I connected to an ssh and lost my connection my tmux would freeze and I had to rebuild the whole structure:

First row:

May 18, 2013

Why Java Calculates Date Time Wrong

I needed to iterate through a date-time range and observed some strange behavior from Java. So I want to iterate hour by hour from 2011-10-05-00 until  2013-02-13-23. The code I was expecting was
DateFormat format = new SimpleDateFormat("yyyy-MM-dd HH");
Calendar c = new GregorianCalendar(2011, 10, 5, 0, 0);  
Calendar cEnd = new GregorianCalendar(2013, 2, 14, 00, 0);
while (c.getTime().before(cEnd.getTime())) {
 System.out.print(format.format(c.getTime()) + "[");
 System.out.println(c.getTimeInMillis() + "](" + cEnd.getTimeInMillis() + ")");
 c.add(Calendar.HOUR, 1);

For some strange reason that I haven't figured out yet this will iterate from 2011-10-05-00 until 2013-03-13 23 (one month later than I'd expected!).

Parse the string first!

May 10, 2013

Vim colorscheme Mustang

I was having some issues setting up a custom color scheme for vim.

Download a colorsheme e.g. mustang from here move it to ~/.vim/colors
In your ~/.vimrc add line
       colorscheme mustang
I was getting

  Error detected while processing /home/morteza/.vimrc:
  line    2:
  E185: Cannot find color scheme mustang
  Press ENTER or type command to continue
To fix this rename

What if your connection drops while you are in the middle of SSH?

If your connection drops in the middle of an ssh session, the TTL of your session will terminate your job running via that session after a while. To avoid

May 1, 2013

Java CPU/Memory Heap Usage Monitoring A.K.A. Java Profiling

Java Profiling: One of the important tools needed when working with java is the use of profiling tools to tell you about the memory consumption and CPU usage of each method. VisualVM is a free and easy to use tool. Java profiling will tell you how heap is being used, Garbage Collector operations, threads activities, CPU time of each method, which object is taking most of memory and etc.

To set it up