Thursday, January 17, 2013

Stashing your changes


Stashing is a great way to pause what you’re currently working on and come back to it later. For example, if you working on that awesome, brand new feature but someone just found a bug that you need to fix. Add your changes to the index using
git add .
Or add individual files to the index, your pick. Stash your changes away with:
git stash
And boom! You’re back to your original working state. Got that bug fixed? Bring your work back with:
git stash apply
 
  You might have stashed more than one, now you want to get the last one.

   git stash pop

   






GIT: How to reset your local branch to master branch


Imagine you have made few local commits and you don't want to commit all of them. Instead you want to go back to the master branch state.
git reset --hard origin/master     // This won't work!

Setting your branch to exactly match the remote branch can be done in two steps
git fetch origin
git reset --hard origin/master

If you want to save your current branch's state before doing this (just in case), you can do:
git commit -a -m "Saving my work, just in case"
git branch my-saved-work


Merging from one branch to other branch


Merging all the commits from one branch to another branch.

For example, currently I am working with 5.5 branch for new features and wanted to pull the changes from 5.0 for fixes which are made.

Currently my branch is pointing to Dev-5.5
$ git merge Dev-5.0

If you have all the 5.0 changes in local system, above command will work fine. 
If your local Dev-5.0 branch is not up-to-date, first pull the changes from central repository.

$ git checkout Dev-5.0

Now you are in Dev-5.0 branch.

$ git pull origin Dev-5.0

This will fetch all the latest commits from origin/Dev-5.0 to local Dev-5.0 branch.

Now, go back to Dev-5.5 branch, to where you want to merge.

$ git checkout Dev-5.5

Now, you are in Dev-5.5 branch.

$ git merge Dev-5.0

This merges Dev-5.0 commits to Dev-5.5 branch, if none of the files having conflicts.

If any file is having conflict, merging will be failed and shows the conflicted files in the console.

Go to the specific files and resolve the conflicts.

Once conflict is resolved, add that file and commit them.

$ Git add hello.java // this is my conflicted file.

$ git status // this will show all the files still need to be merged and including with conflict resolved file.

$ git commit // remaining things are as usual.

Friday, January 11, 2013

Algorithm for random number


I was trying understand the implementation of Java.util.Random implementation but could not crack through it!!

In Java, If we want to generate random number between 1 to 6 (dice game), we can implement like below.

Using  Java.util.Random

public class CheckRandom {

public static void main(String[] args) {
Random random = new Random();
for (int i =0; i< 10;i++) {
int nextInt = random.nextInt(6)+1;
System.out.println(nextInt);
}
}
}

Where random.nextInt(x), uniformly distributed int value between 0 (inclusive) and the specified value (exclusive), drawn from this random number generator's sequence. The general contract of nextInt is that one int value in the specified range is pseudorandomly generated and returned. All n possible int values are produced with (approximately) equal probability.

Using Java.math.random() 
This also works internally based on the java.util.random only. but it generates the values between 0.0 to 1.0.

We can make use of this in the following way to generate random number.
 int diceValue = (int)(Math.random()*6) + 1;



Here is the interesting algorithm for generating a random number. This explains in terms of mathematical expression.
http://www1.i2r.a-star.edu.sg/~knandakumar/nrg/Tms/Probability/Probgenerator.htm



What is a Linear Congruential Random Number Generator?

          Many computer applications rely on random number generation. For example, if you want to write a program to simulate a poker game, you don't want each player to get the same cards every hand. Since some programs require a large number of random numbers, we can greatly speed up the program by using a faster, more efficient random number generator. The method of this  random number generation by linear congruential method, works by computing each successive random number from the previous. Starting with a seed, Xo, the linear congruential method uses the following formula:

Xi+1 = (A*Xi + C) mod M
           In his book, The Art of Computer Programming, Donald Knuth presents several rules for maximizing the length of time before the random number generator comes up with the same value as the seed. This is desirable because once the random number generator comes up with the initial seed, it will start to repeat the same sequence of random numbers (which will not be so random since the second time around since we can predict what they will be). According to Knuth's rules, if M is prime, we can let C be 0 and he suggests that this variant of the line
THEOREM : (By Greenberger in 1961 )

The LCG defined above has full period . if and only if the following conditions are satisfied 

a)      m and c are relatively prime
     b)      If q is a prime number  that divides m , then q divides a-1
    c)      If 4 divides m, then 4 divides a-1
 The LCG tend to behave differently for c>0 and c=0
 A linear congruential generator lnc( ) generates a sequences of integers
                                      U0, U1 ,  ����.   , Uk
that are restricted to the range to m. On each call to lnc( ), you must
give it as argument the previous number in the sequence. It returns the following by
                                       Uk+1   =  ( a Uk +b ) mod (  m + 1).
 where a, b, and can be chosen to be any positive integers. (The operation mod n p is the integer remainder when the integer is divided by the integer p. This remainder must be between 0 and p-1, inclusive.) Once you�ve chosen these three constants and the starting value 0 you�ve completely defined the sequence that lnc( ) will produce. If you set a, b, and to reasonably large values (there are rules of thumb to follow in choosing these values so as the maximize the apparent disorder in the sequence: see Knuth, 1971), the resulting sequence looks satisfyingly random. Of course, you want numbers between 0 and 1, not integers between 0 and m. But you need only divide 1 k U + by m+2 to map the output of lnc into the desired range.

It�s easier to see what lnc( ) is doing if we pick small values a=5, b=1, and m=7. If 0 is set to 2, the resulting sequence is
           
2, 3, 0, 1, 6, 7, 4, 5, 2, 3, 0, 1 �.




Thursday, January 10, 2013

When we will get this debug feature in eclipse ?


When do we get this feature ?

As a java/eclipse developer, will come across this use case everyday. Most of times we wanted to maximize the debug value dialog(I don't know what is this called!) and see the results in one shot.
Expanding and checking the results is really a painful task.



Wednesday, January 9, 2013

Story around Eclipse dropins folder

Generally, if you would like to add new plug-ins we will directly put it into Eclipse\plugins folder and restart the eclipse.

I have joined in a new company, I was wondering why these people are using eclipse dropins folder instead of eclipse plug-ins folder.

Here is the brief story, I found from the below mentioned source.


Do you need the Dropins folder ?

A year ago I had much more inside the Dropins folder then now, because most of the plug-ins in the meantime have a Software-Site.
But if you’re using Plug-ins where no Software Site is available, then the Dropins folder is a great place to store the downloaded Plug-Ins and Features.
It’s easy to use: just copy the Plug-ins (and perhaps features) into the dropins folder.
You’ll find the dropins folder after installation of Eclipse directly inside the eclipse folder:
eclipse/dropins
you can use some different  structures to place the plug-ins into the Dropins folder – I prefer to separate them by domain:
  • /dropins/exampleA/plugins/…
  • /dropins/exampleB/plugins/…
  • /dropins/exampleC/eclipse/features/…
  • /dropins/exampleC/eclipse/plugins/…
The Dropins folder is also very handy if you’re testing some of your  plug-ins.
After copying plug-ins into the Dropins folder its the best to restart Eclipse – if there’s a problem try restarting using -clean (inserted into eclipse.ini)

How To share a Dropins folder ?

If you have some Eclipse installations using same bundles , then you can also share these plug-ins instead of copying them into each installation.
Create a folder like /mySharedDropins anywhere. Inside the folder use the same structure then in your normal Dropins folder.
Now you have to tell your Eclipse that there’s a shared Dropins folder:
Edit eclipse.ini and insert this line:
-Dorg.eclipse.equinox.p2.reconciler.dropins.directory=/<myPath>/mySharedDropins

sources:
http://wiki.eclipse.org/Equinox_p2_Getting_Started
http://ekkescorner.wordpress.com/2009/06/27/galileo-install-plug-ins-into-eclipse-ide/





Tuesday, January 8, 2013

Reading resources from a Eclipse plugin


Project structure:









How do you get the path for services.xml file while you working in plug-in development  ?

String file = "services/services.xml"; //$NON-NLS-1$
String pluginlocation;
try {
Bundle bundle = Platform.getBundle("com.kk"); //my class pkg
URL pLocationUrl = FileLocator.find(bundle, new Path("/"), null);
URL pFileUrl = FileLocator.toFileURL(pLocationUrl);
pluginlocation = pFileUrl.getFile();
} catch (IOException e) {
//log error
}


String completePath = pluginlocation.append(File.separator).append(file);