Monday, December 31, 2012

SoftHashMap - hashmap with soft values

The biggest problem with WeakHashMap is, it will only weakly reference the keys but not the values. This may lead to memory issues if we are using weakhashmap as a cache.

We can try this!!

import java.lang.ref.ReferenceQueue;
import java.lang.ref.SoftReference;
import java.util.AbstractMap;
import java.util.HashMap;
import java.util.LinkedList;
import java.util.Map;
import java.util.Set;

public class SoftHashMap<K, V> extends AbstractMap<K, V> {

/** The internal HashMap that will hold the SoftReference. */
private final Map<K, SoftValue<V>> hash = new HashMap<K, SoftValue<V>>();

/** The number of "hard" references to hold internally. */
private final int HARD_SIZE;

/** The FIFO list of hard references, order of last access. */
private final LinkedList<V> hardCache = new LinkedList<V>();

/** Reference queue for cleared SoftReference objects. */
private final ReferenceQueue queue = new ReferenceQueue();

public SoftHashMap() {

public SoftHashMap(int hardSize) {
HARD_SIZE = hardSize;

public V get(Object key) {
V result = null;
// We get the SoftReference represented by that key
SoftReference<V> soft_ref = hash.get(key);
if (soft_ref != null) {
// From the SoftReference we get the value, which can be
// null if it was not in the map, or it was removed in
// the processQueue() method defined below
result = soft_ref.get();
if (result == null) {
// If the value has been garbage collected, remove the
// entry from the HashMap.
} else {
// We now add this object to the beginning of the hard
// reference queue. One reference can occur more than
// once, because lookups of the FIFO queue are slow, so
// we don't want to search through it each time to remove
// duplicates.
if (hardCache.size() > HARD_SIZE) {
// Remove the last entry if list longer than HARD_SIZE
return result;

* We define our own subclass of SoftReference which contains not only the
* value but also the key to make it easier to find the entry in the HashMap
* after it's been garbage collected.
private static class SoftValue<V> extends SoftReference<V> {
private final Object key; // always make data member final

private SoftValue(V obj, Object key, ReferenceQueue queue) {
super(obj, queue);
this.key = key;

* Here we go through the ReferenceQueue and remove garbage collected
* SoftValue objects from the HashMap by looking them up using the
* SoftValue.key data member.
private void processQueue() {
SoftValue sv;
while ((sv = (SoftValue) queue.poll()) != null) {
hash.remove(sv.key); // we can access private data!

* Here we put the key, value pair into the HashMap using a SoftValue
* object.
public V put(K key, V value) {
processQueue(); // throw out garbage collected values first
SoftValue<V> softValue = new SoftValue<V>(value, key, queue);
SoftValue<V> put = hash.put(key, softValue);
if (put != null) {
return put.get();
return null;

public V remove(Object key) {
processQueue(); // throw out garbage collected values first
SoftValue<V> remove = hash.remove(key);
if (remove != null)  {
return remove.get();
return null;

public void clear() {
processQueue(); // throw out garbage collected values

public int size() {
processQueue(); // throw out garbage collected values first
return hash.size();

public Set entrySet() {
throw new UnsupportedOperationException();

Eclipse author ${user} variable

Here is a small “hack” which can put anything you want in this ${user} variable.

Add one more variable in the eclipse.ini file with the following.
-vmargs"your name here..." 

Rather than having to change the template manually, add 
-vmargs"your name here" to the shortcut you use to run Eclipse ( by right clicking on it, selecting properties and editing the target input field) :
C:/java/eclipse/eclipse.exe -vmargs"your name here.."

Sunday, December 30, 2012

Force overwrite on git pull

How do I force an overwrite of local files on a git pull?

git fetch --all
git reset --hard origin/master
git fetch downloads the latest from remote without trying to merge or rebase anything. 
Then thegit reset resets the master branch to what you just fetched

Thursday, December 27, 2012

Image decorator

Here is the simple snippet to add a decorator to the image.

public Image getImage(Object element) {

if (resource instanceof Column)
 return decorateImage(SImageRegistry.getImage(SImageConstants.column), element);


public Image decorateImage(Image image, Object element) {
if (element instanceof Column) {
if (((Column) element).isPrimaryKeyPart()) {
DecorationOverlayIcon decorationOverlayIcon = new DecorationOverlayIcon(image,
SImageRegistry.getImageDescriptor(SImageConstants.primary_key), IDecoration.TOP_LEFT);
return decorationOverlayIcon.createImage();
return image;
return null;

Wednesday, December 5, 2012

Increase heap size to your eclipse

Here is the example to specify the eclipse vm arguments in eclipse.ini file to avoid eclipse memory issues during your development.


If you are working with eclipse plug-in development, while launching your eclipse application you have to specify the vm arguments so that it will be available for your target platform as well.
Please find the screenshot below to configure it.

Wednesday, November 28, 2012

Collections emptyList()

Can you guess the output for the below program ?
import java.util.Collections;
import java.util.List;

public class CollectionsTest {

private List<String> pool = Collections.<String> emptyList();

public List<String> call1() {
return pool;

public static void main(String[] args) {
CollectionsTest collectionsTest = new CollectionsTest();
List<String> call1 = collectionsTest.call1();
call1.add("one more added..");


Exception in thread "main" java.lang.UnsupportedOperationException
at java.util.AbstractList.add(
at java.util.AbstractList.add(
at CollectionsTest.call1(
at CollectionsTest.main(

In short:
Collections.emptyList() returns an immutable list, i.e., a list to which you cannot add or remove elements.

Then, why should we use at all ? What is the purpose of this ?

Best Regards,
Kondal Kolipaka

My JAXB Learnings - Part 2

As part of this post, you will be understanding on the following concepts in the JAXB through an example.

1. Defining the name space
2. Defining the wrapper elements in the XML
3. Setting the name for entities in the list.
4. Defining the order for elements

This example is based on the book store and book model objects.

import javax.xml.bind.annotation.XmlElement;
import javax.xml.bind.annotation.XmlRootElement;
import javax.xml.bind.annotation.XmlType;

@XmlRootElement(name = "myBook")
// If you want you can define the order in which the fields are written
// Optional
@XmlType(propOrder = { "author", "name", "publisher", "isbn" })
public class Book {

private String name;
private String author;
private String publisher;
private String isbn;

// If you like the variable name, e.g. "name", you can easily change this
// name for your XML-Output:
@XmlElement(name = "titleName")
public String getName() {
return name;

public void setName(String name) { = name;

public String getAuthor() {
return author;

public void setAuthor(String author) { = author;

public String getPublisher() {
return publisher;

public void setPublisher(String publisher) {
this.publisher = publisher;

public String getIsbn() {
return isbn;

public void setIsbn(String isbn) {
this.isbn = isbn;



import java.util.ArrayList;

import javax.xml.bind.annotation.XmlElement;
import javax.xml.bind.annotation.XmlElementWrapper;
import javax.xml.bind.annotation.XmlRootElement;

//This statement means that class "" is the root-element of our example
@XmlRootElement(namespace = "com.kondal.bookstore.model")
public class BookStore {

// XmLElementWrapper generates a wrapper element around XML representation
@XmlElementWrapper(name = "bookList")

// XmlElement sets the name of the entities
@XmlElement(name = "book")
private ArrayList<Book> bookList;
private String name;
private String location;

public void setBookList(ArrayList<Book> bookList) {
this.bookList = bookList;

public ArrayList<Book> getBooksList() {
return bookList;

public String getName() {
return name;

public void setName(String name) { = name;

public String getLocation() {
return location;

public void setLocation(String location) {
this.location = location;

3. BookMain 

import java.util.ArrayList;

import javax.xml.bind.JAXBContext;
import javax.xml.bind.JAXBException;
import javax.xml.bind.Marshaller;
import javax.xml.bind.Unmarshaller;

public class BookMain {

private static final String BOOKSTORE_XML = "./BookStore-jaxb.xml";

public static void main(String[] args) throws JAXBException, IOException {

ArrayList<Book> bookList = new ArrayList<Book>();

// create books
Book book1 = new Book();
book1.setName("The Game");
book1.setAuthor("Neil Strauss");

Book book2 = new Book();
book2.setAuthor("Charlotte Roche");
book2.setPublisher("Dumont Buchverlag");

// create BookStore, assigning book
BookStore BookStore = new BookStore();
BookStore.setName("Fraport BookStore");
BookStore.setLocation("Frankfurt Airport");

// create JAXB context and instantiate marshaller
JAXBContext context = JAXBContext.newInstance(BookStore.class);
Marshaller m = context.createMarshaller();
m.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, Boolean.TRUE);

// Write to System.out
m.marshal(BookStore, System.out);

// Write to File
m.marshal(BookStore, new File(BOOKSTORE_XML));

// get variables from our xml file, created before
System.out.println("Output from our XML File: ");
Unmarshaller um = context.createUnmarshaller();
BookStore bookstore2 = (BookStore) um.unmarshal(new FileReader(
ArrayList<Book> list = bookstore2.getBooksList();
for (Book book : list) {
System.out.println("Book: " + book.getName() + " from "
+ book.getAuthor());

Output on console:

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<ns2:bookStore xmlns:ns2="com.kondal.bookstore.model">
            <author>Neil Strauss</author>
            <titleName>The Game</titleName>
            <author>Charlotte Roche</author>
            <publisher>Dumont Buchverlag</publisher>
    <location>Frankfurt Airport</location>
    <name>Fraport BookStore</name>

Output from our XML File:
Book: The Game from Neil Strauss
Book: Feuchtgebiete from Charlotte Roche

Tuesday, November 27, 2012

Get started with JAXB

If you are a beginner for JAXB. Here is the simple example will help you to get started.

All you need to have is JDK environment. This comes along with JAXB implementation.

This particular example is based upon the customer data, which deals with marshaling and unmarshaling.

Work flow:
1. Define your customer class, and identify the elements and attributes as part of  it.

import javax.xml.bind.annotation.XmlAttribute;
import javax.xml.bind.annotation.XmlElement;
import javax.xml.bind.annotation.XmlRootElement;

public class Customer {

String name;
int age;
int id;

public String getName() {
return name;

public void setName(String name) { = name;

public int getAge() {
return age;

public void setAge(int age) {
this.age = age;

public int getId() {
return id;

public void setId(int id) { = id;


2. Using JAXB Context do the marshaling.

import javax.xml.bind.JAXBContext;
import javax.xml.bind.JAXBException;
import javax.xml.bind.Marshaller;

public class CustomerJAXBMarshal {
public static void main(String[] args) {

Customer customer = new Customer();

try {

File file = new File("C:\\Customer.xml");
JAXBContext jaxbContext = JAXBContext.newInstance(Customer.class);
Marshaller jaxbMarshaller = jaxbContext.createMarshaller();

// output pretty printed
jaxbMarshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);

jaxbMarshaller.marshal(customer, file);
jaxbMarshaller.marshal(customer, System.out);

} catch (JAXBException e) {


Output on console:

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<customer id="100">

3.  Unmarshal the Customer XML file to build the Customer run time object.

import javax.xml.bind.JAXBContext;
import javax.xml.bind.JAXBException;
import javax.xml.bind.Unmarshaller;

public class CustomerJAXBUnmarshal {
public static void main(String[] args) {

try {

File file = new File("C:\\Customer.xml");
JAXBContext jaxbContext = JAXBContext.newInstance(Customer.class);

Unmarshaller jaxbUnmarshaller = jaxbContext.createUnmarshaller();
Customer customer = (Customer) jaxbUnmarshaller.unmarshal(file);

} catch (JAXBException e) {


Output on console:

Monday, November 26, 2012

Git squash all commits into a single commit

$ git rebase -i 
Remember again that this is a rebasing command. Don’t include any commit you’ve already pushed to a central server — doing so will confuse other developers by providing an alternate version of the same change.
Running this command gives you a list of commits in your text editor that looks something like this:
pick f7f3f6d changed my name a bit
pick 310154e updated README formatting and added blame
pick a5f4a0d added cat-file

# Rebase 710f0f8..a5f4a0d onto 710f0f8
# Commands:
#  p, pick = use commit
#  e, edit = use commit, but stop for amending
#  s, squash = use commit, but meld into previous commit
# If you remove a line here THAT COMMIT WILL BE LOST.
# However, if you remove everything, the rebase will be aborted.
It’s important to note that these commits are listed in the opposite order than you normally see them using the log command. If you run a log, you see something like this:
$ git log --pretty=format:"%h %s" HEAD~3..HEAD
a5f4a0d added cat-file
310154e updated README formatting and added blame
f7f3f6d changed my name a bit
Notice the reverse order. The interactive rebase gives you a script that it’s going to run. It will start at the commit you specify on the command line and replay the changes introduced in each of these commits from top to bottom. It lists the oldest at the top, rather than the newest, because that’s the first one it will replay.

It’s also possible to take a series of commits and squash them down into a single commit with the interactive rebasing tool. The script puts helpful instructions in the rebase message:
# Commands:
#  p, pick = use commit
#  e, edit = use commit, but stop for amending
#  s, squash = use commit, but meld into previous commit
# If you remove a line here THAT COMMIT WILL BE LOST.
# However, if you remove everything, the rebase will be aborted.
If, instead of "pick" or "edit", you specify "squash", Git applies both that change and the change directly before it and makes you merge the commit messages together. So, if you want to make a single commit from these three commits, you make the script look like this:
pick f7f3f6d changed my name a bit
squash 310154e updated README formatting and added blame
squash a5f4a0d added cat-file
When you save and exit the editor, Git applies all three changes and then puts you back into the editor to merge the three commit messages:
# This is a combination of 3 commits.
# The first commit's message is:
changed my name a bit

# This is the 2nd commit message:

updated README formatting and added blame

# This is the 3rd commit message:

added cat-file
When you save that, you have a single commit that introduces the changes of all three previous commits.

Cherry-Picking specific commits from one branch to another

Say, for example you are working with two different branches. Dev-4.0 and Dev-5.0.

And you have made few changes/fixes in Dev-4.0 branch and now you want to bring those changes in to the Dev-5.0 branch.

GIT provides cherry-pick command to do that.

1. Go to Dev-4.0 branch and identify the commit id's which need to be cherry-picked.
ex: Below the commit id's for my changes in Dev-4.0 branch.


2. Go to Dev-5.0 branch and fire the following command.

> git cherry-pick  8ae534e23d82070cdaaea4913415678affdab44b

this will bring all your commit changes from Dev-4.0 to  Dev-5.0

If you have any conflicts during this time.
- Resolve the conflicting files
- Once you have resolved the issues, add them to git if it's not added.
- Commit the modified files.

Otherwise git automatically commit your changes with cherry-pick command itself, if there are no conflicts occurred.


Now..hope you are good to go!!.

Sunday, November 25, 2012

Checking user specific commits in GIT

> To filter your commit history to only the ones done by a specific author.

           git log

 > -[number] option, which will limit the results to the last [number] commits.

         git log  -4

> git log --since --before filter commits by date committed

If you want to specify a date range that you're interested in filtering your commits down to, you can use a number of options - I use --since and --before, but you can also use --until and --after. For example, if I wanted to see all the commits in the Git project before 3 weeks ago but after April 18th, I could run this (I'm also going to use --no-merges to remove merge commits):

     git log --oneline --before={3.weeks.ago} --after={2012-11-18} --no-merges

> git log --grep filter commits by commit message
You may also want to look for commits with a certain phrase in the commit message. You can use --grep for that. Let's say I knew there was a commit that dealt with using the P4EDITOR environment variable and I wanted to remember what that change looked like - I could find the commit with --grep.

    git log --grep=P4EDITOR --no-merges

Friday, November 23, 2012

Tooltip on tree viewer items

This describes about how to add a tooltip on tree viewer items based on the context of object. 

ExplorerViewer.getTree().addMouseTrackListener(new ExplorerMouseListener());

private class ExplorerMouseListener implements MouseTrackListener {

public void mouseEnter(MouseEvent e) {

public void mouseExit(MouseEvent e) {

public void mouseHover(MouseEvent event) {

TreeItem item = explorerViewer.getTree().getItem(new Point(event.x, event.y));
if (item != null && item.getData() instanceof MyResource) {
MyResource selectedElement = (MyResource) item.getData();
if (selectedElement.getResourceType() == MyResourceType.APP_GROUP
|| selectedElement.getResourceType() == MyResourceType.DATA) {
if (selectedElement.getData() instanceof INameDescription)
((INameDescription) selectedElement.getData())
} else {


Template for git commit messages

Good commit messages always makes a difference!!!

Following is the template I generally refer to.

FEATURE/BUGFIX/ENHANCEMENT: KonyOne Studio - <Module name> - <short problem/module description>

<Detailed description of feature/solution description/enhancement comments>

<Fix: #JSP1234>

Reviewed By :  <reviewer name>

Example for Feature:

FEATURE: KonyOne Studio - Sky Data Explorer - Implemented model classes for sky explorer

Provided the offline support capabilities to work offline.

Reviewed by: Rakesh 

Example for BugFix:

BUGFIX: KonyOne Studio - Java Script Module - Heap memory issues with huge number of files.

Java script listener is modified..etc,..

Fix: #JSP12345

Example for Enhancement:

ENHANCEMENT: KonyOne Studio - Java Script Module - code clean for java script model

Unnecessary code has been removed in java script module.

Reviewed by: Rakesh 

Points to be considered:

  • Topic description (first line)
  •  72 characters max for each line.
  •  Give space for title and body
  •  Use present tense.(Generally git uses the same for merge/rebase)

Why 72 characters ??
git log doesn’t do any special special wrapping of the commit messages. 

On an 80 column terminal, if we subtract 4 columns for the indent on the left and 4 more for symmetry on the right, we’re left with 72 columns.

Good commit messages serve at least three important purposes:

  • To speed up the reviewing process.
  • To help us write a good release note.
  • To help the future maintainers (it could be you!), say five years into the future, to find out why a particular change was made to the code or why a specific feature was added.

Friday, August 31, 2012

Eclipse OSGI framework


I have found very interesting links which explains about OSGI framework.

Basic understaing on OSGI

Very very interesting article on Eclipse open source architecture

Thursday, July 12, 2012

Discard unstaged changes in GIT

You might have lot of unstaged files, which you dont want to submit to GIT. You can use CHECKOUT option from the git to do this.

1. Removing a single file
   >git checkout <filename>

2. Removing all unstaged files.
  >git checkout reset --hard

3. Sometimes, option (2) does not work. you can use the following option.
  > git checkout -- .

Make sure to include the period at the end of command.