Be Happy

Perl

2012-02-08T08:27:00.000-08:00

Download perl from ActivePerl website and install it. It will automatically set the path and environment variable.

Perl is useful as it process one line from the file at a time. Each line is stored in $_ variable.

Combinatorial Optimization

2012-02-04T22:13:00.001-08:00

Combinatorial Optimization
http://en.wikipedia.org/wiki/Combinatorial_optimization

My research

2012-02-04T20:20:00.000-08:00

Research Interests:

· Combinatorial Machine Learning,

· Decision tree, test & rules,

· Many Valued Decisions,

· Artificial Intelligence,

· Artificial Neural Network (ANN)

Books that I read

2012-02-04T20:13:00.000-08:00

1. Machine Learning
2. Data Mining
3. Combinatorial Machine Learning
4. Concepts of Programming Languages
5. Algorithms
6. Artificial Intelligence
7. Computer Architecture
8. Computer Networks
9. Operating Systems

Search Engine

2009-05-05T02:31:00.001-07:00

How search engine works:

Animated learning: http://www.learnthenet.com/english/animate/search.html
How stuff works: http://computer.howstuffworks.com/search-engine.htm
Search engine watch: http://searchenginewatch.com/2168031

Search Engine Ranking

2009-05-05T01:49:00.000-07:00

How Search Engines Rank Web Pages

How do crawler-based search engines go about determining relevancy, when confronted with hundreds of millions of web pages to sort through? They follow a set of rules, known as an algorithm. Exactly how a particular search engine's algorithm works is a closely-kept trade secret.

http://searchenginewatch.com/2167961

Computer Science papers

2009-05-05T01:27:00.000-07:00

Papers in Computer Science is a blog for abstracts and brief summaries and discussions about published computer science articles, updated 3 times a week.

http://papersincomputerscience.org/category/artificial-intelligence/

How to memorize words

2009-01-30T02:25:00.000-08:00

Use Mnemonic.

http://sites.google.com/site/mygreguidebook/mnemonics

Mnemonics - The ultiamte word memorization tricks

Before sitting for the GRE, I sorted out some techniques to remeber a word, called 'MNEMONICS'. Everyone has their own mnemonics. You have to sort out yours.

These are my mnemonics:

1. Never learn a new word by rote learning, means Memorization by repetition. Rather try to visualize a word in your mind. as example, the word 'copse' means 'A dense growth of bushes', now when u think the word copse, close your eyes and visualize it like the bushes u c in the gardens. And also think that, the "copse" also SOUNDS like bushes. Got it?

2. Always interrelate your ideas and find links to remember. Suppose the word "SPLICE" means "to join or tie". Now the word "SLICE" means "Cut into pieces". See the relation between the words "slice" and "splice". They sound very similar but means opposite. Another similar example is " EXTINCT" an " EXTANT". Try to find linkage between words in your own way. Each person has their different and unique way of thinking. Find and use yours. You can relate with your mother tongue language words too.

3. The best way to memorize a word is by learning the word’s ETYMOLOGY (The study of the sources and development of words). In this way you can learn several words at a time.

Like ‘Philanthropist’ and ‘Philanderer’ have the common root ‘Phil-‘(means ‘Love for something’).
While, the meanings are ‘Philanthropist =Someone who makes charitable donations intended to increase human well-being'
'Philanderer= A man who likes many women and has short sexual relationships with them'
Again, 'Philanthropist' has another root 'Anthropo-' (means ‘human/mankind’)
Some more words from this root are : Anthropology, Anthropomorphic, Anthropoid.

You can learn more words by this means. Well, you can go to http://www.mnemonicdictionary.com or http://www.thefreedictionary.com for word origins or etymology.

4. Always learn at least two words at a a time. When you larn a new word, learn all its synonyms, at least one. You might not remember them but all at once, but eventually it will help.
For now, Philanthropist= altruist, Philanderer= womanizer
In this way if you memorize 3000 words, it becomes 6000. :D

5. Learn the words by listening to the audio.

6. Also try to larn words through pictures. Larning proper nouns by this system is pretty effective. The link:
http://www.ziddu.com/download/1866674/LarnwordsthroughPictures.zip.html

7. Use WORD WEB dictionary. Go to www.download.com and search it. This software rocks.

8. Finally, Practice is the ultimate goal of success in GRE. Unless you practice nothing's gonna help you. It doesn't really matter how strong is your vocabulary part. Because, practice shows us where we are committing mistakes and what are the notches that needs to be filled. I am repeating the dialog verbatim "There is no other way than practice and revise".

Hope you will ‘eat words, drink words, sleep words and dream words’ till you sit for the exam.

Best of luck.

Difference between HTTP and HTTPs

2009-01-29T04:19:00.000-08:00

Http is hyper text transfer protocol which is responsible for transmitting and receiving information across the Internet where as https is secure http, which is used exchanging confidential information with a server, which needs to be secured in order to prevent unauthorized access.

HTTP is Hyper Text Transport Protocol and is transmitted over the wire via PORT 80(TCP). You normally use HTTP when you are browsing the web, its not secure, and so someone can eavesdrop on the conversation between your computer and the web server. HTTP can support the client asking for a particular file to be sent only if it has been updated after a certain date and time. This would be used if the client has already retrieved a copy of a file by that name from that server, but wants to check to see if it has been updated since then. The server responds either with the updated file, with a message to say the file has not been changed, or with a message that the file no longer exists.

HTTPS (Hypertext Transfer Protocol over Secure Socket Layer or HTTP over SSL) is a Web protocol developed by Netscape and built into its browser that encrypts and decrypts user page requests as well as the pages that are returned by the Web server. HTTPS is really just the use of Netscapes Secure Socket Layer (SSL) as a sub layer under its regular HTTP application layering. (HTTPS uses port 443 instead of HTTP port 80 in its interactions with the lower layer, TCP/IP.) SSL uses a 40-bit key size for the RC4 stream encryption algorithm, new-age browsers use 128-bit key size which is more secure than the former, it is considered an adequate degree of encryption for commercial exchange. HTTPS is normally used in login pages, shopping/commercial sites.

xml String parsing in C#

2008-12-02T05:54:00.000-08:00

I have faced problems for parsing xml string in C#. I have solved in the following ways:

Instead of give the actual string to the XmlTextReader

XmlTextReader reader = new XmlTextReader(result);

You should pass with the help of StringReader Object.

XmlTextReader reader = new XmlTextReader(new System.IO.StringReader(result));

All about scope

2008-11-05T08:07:00.001-08:00

Request
Page
Session
Application

If you have a request scope, it will only run for the request that is made on that same moment.
If you have a page scope, the parameters and values will run for that page the whole time until the server is restarted.
If you have a session scope, all the values will be kept for until the clients session is destroyed.
And least the application scope, if you apply the application scope, the values will be kept for the entire application, until the server is restarted.

Chain of Responsibility Pattern

2008-08-26T22:00:00.000-07:00

The classic Chain of Responsibility(CoR) pattern defined by Gang of Four(GoF) in Design Patterns:

"Avoid coupling the sender of a request to its receiver by giving more than one object a chance to handle the request. Chain the receiving objects and pass the request along the chain until an object handles it."

Following Figure illustrates the class diagram.

Figure 1. CoR class diagram

A typical object structure might look like following Figure .

Figure 2. CoR object structure

From the above illustrations, we can summarize that:

Multiple handlers may be able to handle a request
Only one handler actually handles the request
The requester knows only a reference to one handler
The requester doesn't know how many handlers are able to handle its request
The requester doesn't know which handler handled its request
The requester doesn't have any control over the handlers
The handlers could be specified dynamically
Changing the handlers list will not affect the requester's code

Uses of CoR:
1. Microsoft Windows global hook framework
2. Java servlet filter framework

Details are explained by Michael Xinsheng Huang, JavaWorld.com, 08/16/04

Difference between Association, Aggregation and composition

2008-08-18T23:34:00.000-07:00

Difference between Association, Aggregation and composition:

Association:


1. A relationship between 2 objects that is not whole-part i.e.
A contains a reference of B and uses B through the reference
2. Generally implemented as a public property of A,
where B may be set in to A by an external party (say Spring)

Dependency:

1. A week association, where A doesnt contain a reference of B but uses B
2. Generally implemented as method parameter in A

Composition:

1. A strong whole-part relationship, i.e. B (child) has no existence
outside A (parent)
2. A creates and contains B but B can not contain A
2. B must not be visible outside of A since if A dies, B must die

Aggregation:

1. A week whole-part relationship, i.e.  B (child) may exist exist
outside A (parent)
2. A contains B but B can not contain A
3. B must be visible outside of A since B may still exist when A dies
4. Generally 1-many relationship

With Real Life Examples:

Accosiation:
1. Create a folder called "Links"
2. create a shortcut inside this folder and link it to www.yahoo.com
3. create another shortcut instide this folder and link it to www.google.com
4. Ask your friend to do the same on another machine using same links
(www.yahoo.com and www.google.com)
5. Delete the "Links" folder, and open your browser to check if
www.yahoo.com and www.google.com still exist or not ;)

Briefly, Association is a relationship where all the objects have different lifecycles.
There is no owner.



Composition:
1. Open a new Document name it as test.txt
2. Write this sentence in iside this document "This is a composition".
3. Save the document.
4. Now, delete this document.

This is what is called composition, you can't move the sentence "This is a
composition" from the document because its lifecycle is linked to the
parent (the document)

Aggregation:
1. Create a file called file.txt
2. make a simple application to open the file.txt (rw), but don't program
it close the connection.
3. Run an instance of this application (it should work ok and can open the file for rw)
4. Keep the first instance, and run another instance of this application
(In theory it should complain that it can't open the file in rw mode
because it is already used by other application).
5. Close the 2 instances (make sure you close the connection).

From the above application, we knew that the Application and the file has a
separate lifecycles, however this file can be opened only by one
application simuletanously (there is only one parent at the same time,
however, this parent can move the child to another parent or can make
it orphan).


View Details: http://www.artima.com/forums/flat.jsp?forum=17&thread=24715

Use globally defined constants

2008-04-30T02:24:00.001-07:00

You can use globally defined constants by defining them inside a class and referencing themwithout instantiation.

 public class CONSTANT {

  public static final integer SUCCESS = 1;
  public static final integer FAILURE = -1;
  public static final integer NOTFOUND = 0;

}

Since the members of the class are defined as "static", there is no need to instantiate the class. To use a constant, simply use CONSTANT.[constant name]

 if (myMethod()==CONSTANT.SUCCESS) {
   ...;
}
else {
   ...;
}

For details: Java Tips

Set the memory available to the JVM

2008-04-30T02:14:00.000-07:00

By default, the JVM will use up to 16Mb of RAM. If your program allocates a lot of memory, you may need to increase this value to give more room to the garbage collector.

When starting the JVM, two parameters can be adjusted to suit your memory needs:

-mx n Sets the maximum size of the memory allocation pool where n is in bytes, appending "m" to n will specified the number in megabytes, for example to set the maximum at 20Mb:

   java -mx 20m myApp

. -ms n Sets the startup size of the memory allocation pool, where n is in bytes, appending "m" to n will specified the number in megabytes. The default is 1Mb.

With JDK1.2, that syntax have changed, no space between ms/mx and the value:

   java -mx20m myApp

For Details: Java Tips

Pass an integer by reference

2008-04-30T02:04:00.000-07:00

Sometimes you may need to pass an integer to be able to change its value. "integer" are always passed by value in Java. An easy way to pass by reference is to use a single element array.

 int[] a = new int[1];
a[0] = 1;
add2(a);
// a[0] now = 3
...

void add2(int[] a) {
    a[0] = a[0] + 2;
}

For details: Java Tips

Make a JAR executable

2008-04-30T02:02:00.000-07:00

In the manifest file of a JAR, it is possible to specify the class to be used when the JVM is lauched with the JAR as parameter. The class must have a main().

Try with this simple class:

 import java.awt.*;
import java.awt.event.*;

public class MyClass {
 public static void main(String[] args) {
    Frame f = new Frame();
    f.addWindowListener
          (new WindowAdapter() {
              public void windowClosing(WindowEvent e) {
                 System.exit(0);
                 }
              }
    );
    f.add(new Label("Hello world"));
    f.setSize(200,200);
    f.setVisible(true);
   }
}

Then create this manifest file (manifest.mft) with any text editor.

   Manifest-Version: 1.0
  Main-Class: MyClass
  Classpath: .\MyJar.jar

Next, you include the manifest file in the JAR (MyJar.jar) with the MyClass class.

   jar cvfm MyJar.jar manifest.mft MyClass.class

Then you are able to start the MyClass.class by double-clicking on the MyJar.jar file (if the JRE is correctly installed) or by typing

   java -jar MyJar.jar

On NT, you can also make JARs run from the command-line by setting the PATHEXT environment variable, for example

   set PATHEXT=.EXE;.BAT;.CMD;.JAR

Then if you have the jar file MyJar.jar accessible via the PATH environment variable, typing "MyJar" on the DOS command line will invoke "java -jar MyJar.jar" .

For Details: Java Tips

Introduction to Autoboxing

2008-04-30T01:56:00.000-07:00

This Tech Tip reprinted with permission by java.sun.com

Although the Java programming language is an object-oriented language, it's often the case that when using the language you need to work with primitive types. Before J2SE 5.0, working with primitive types required the repetitive work of converting between the primitive types and the wrapper classes. In this tip, you will see how the new autoboxing feature in J2SE 5.0 handles conversions -- for example, between values of type int and values of type Integer. The tip also discusses some autoboxing-related considerations in determining when two numerical values are equal.

The October 5, 2004 Tech Tip, Formatting Output with the New Formatter discussed a new way to format output that is similar to that of the C language's printf. An example in that tip used the printf() method to print an integral value. Here is a simple example that uses the printf() method:

    public class FormatPrint {
     public static void main(String[] args) {
       System.out.printf("There is only %d thing.", 1);
     }
   }

The signature of the printf() method in the FormatPrint example is:

   printf(String format, Object... args)

The number 1 is a primitive and not an object, so you might think that the line:

   System.out.printf("There is only %d thing.", 1);

should not compile. However autoboxing takes care of the situation by automatically wrapping the integer value in the appropriate wrapper object. In J2SE 1.4 you would have needed to manually wrap the primitive value using something like new Integer(1).

Another example of where automatically converting from a primitive might be useful is when you use the Collections APIs. The collections classes are designed to store objects. Consider the following simple example of storing int values from 0 to 9 in an ArrayList:

    import java.util.ArrayList;

    public class Autoboxing {
      public static void main(String[] args) {
          ArrayList list = new ArrayList();
          for(int i = 0; i < 10; i++){
             list.add(i);
          }
      }
    }

The comparable program for J2SE 1.4.2 would be the following:

    import java.util.ArrayList;

   public class ManualBoxing {
     public static void main(String[] args) {
        ArrayList list = new ArrayList();
        for(int i = 0; i < 10; i++){
            list.add(new Integer(i));
        }
     }
   }

With ManualBoxing you need to explicitly create the Integer object using list.add(new Integer(i)). Contrast that with Autoboxing, where the int i is autoboxed to an Integer object in the line list.add(i).

Autoboxing works well with other new J2SE 5.0 features. For example, the autoboxing feature allows seamless integration between generic types and primitive types. In the ManualBoxing example, the elements of the ArrayList are of type Object. By comparison, in the Autoboxing example, the elements of list are of type Integer.

Let's extend the Autoboxing example to iterate through the elements in the ArrayList and calculate their sum. Notice that this new version also uses the new J2SE 5.0 enhanced for loop to iterate through the elements.

    import java.util.ArrayList;
   
     public class Autoboxing {
       public static void main(String[] args) {
           ArrayList list = new ArrayList();
           for(int i = 0; i < 10; i++){
              list.add(i);
           }
           int sum = 0;
          for ( Integer j : list){
            sum += j;
          }
         System.out.printf("The sum is %d.", sum );
       }
     }

Autoboxing is used in a number of places in the updated Autoboxing example. First, ints are boxed to Integers as they are added to the ArrayList. Then Integers are unboxed to ints to be used in calculating the sum. Finally, the int representing the sum is boxed for use in the printf() statement.

The transparency of the boxing and unboxing makes autoboxing easy to use. However using the autoboxing feature requires some care. In particular, testing for the equality of objects created by autoboxing is not the same as testing for the equality of objects that are not created by autoboxing. To see this, look at the following BoxingEquality class:

    import java.util.ArrayList;
   
     public class BoxingEquality {
       public static void main(String[] args) {
          int i = 2;
          int j = 2;
          ArrayList  list = new ArrayList();
          list.add(i);
          list.add(j);
          System.out.printf("It is %b that i ==j.\n",
                            (i==j)); //(1)
          System.out.printf("It is %b that " +
                            "list.get(0) == list.get(1).\n",
                            list.get(0)==list.get(1)); //(2)
          System.out.printf("It is %b that " +
                         "list.get(0).equals(list.get(1)).",
                         list.get(0).equals(list.get(1))); //(3)
        }
     }

The first print statement in BoxingEquality compares the equality of the primitives i and j. The second print statement compares the equality of the objects created by autoboxing i and j. The third print statement compares the value of the objects created by autoboxing i and j. You would expect the first and the third print statements to return true, but what about the second? The output from running the BoxingEquality program is:

   It is true that i ==j.
  It is true that list.get(0) == list.get(1).
  It is true that list.get(0).equals(list.get(1)).

Now change the values of i and j to 2000.

    import java.util.ArrayList;

   public class BoxingEquality {
     public static void main(String[] args) {
       int i = 2000;
       int j = 2000;
       // . . .
   }

Save, recompile, and rerun BoxingEquality. This time the results are different:

   It is true that i ==j.
  It is false that list.get(0) == list.get(1).
  It is true that list.get(0).equals(list.get(1)).

The primitives are equal and the values of the boxed ints are equal. But this time the ints point to different objects. What you have discovered is that for small integral values, the objects are cached in a pool much like Strings. When i and j are 2, a single object is referenced from two different locations. When i and j are 2000, two separate objects are referenced. Autoboxing is guaranteed to return the same object for integral values in the range [-128, 127], but an implementation may, at its discretion, cache values outside of that range. It would be bad style to rely on this caching in your code.

In fact, testing for object equality using == is, of course, not what you normally intend to do. This cautionary example is included in this tip because it is easy to lose track of whether you are dealing with objects or primitives when the compiler makes it so easy for you to move back and forth between them.

For more information on autoboxing, see Autoboxing.

For details: Java Tips

How to write a Java Application without a main method

2008-04-30T01:33:00.000-07:00

You can write a runnable Java program which does not have main method at all. This can be done using the static block of the class.

The reason this works is that static initialization blocks get executed as soon as the class is loaded, even before the main method is called. During run time JVM will search for the main method after exiting from this block. If it does not find the main method, it throws an exception. To avoid the exception System.exit(0); statement is used which terminates the program at the end of the static block itself.

 class MainMethodNot
{
    static
    {
        System.out.println("This java program have run without the run method");
        System.exit(0);
        
    }
}

Fore details: Java Tips

Array, List and Map Differences...

2008-04-30T00:45:00.000-07:00

The measured times show that for random operations within a list, it's preferable to use the array or the ArrayList. There's no real difference in performance between the array and the ArrayList, so if you need the extra features of an ArrayList, then it's the obvious choice. You should only consider using LinkedList when your operations work on the ends of the list. Another option to consider might be the new Queue class-- when only the top element of a list is of interest.

When the index or key to the list is not an integer, HashMap is the only choice, and as you've seen, its performance is quite good.

For details: Java Boutique

How to use getenv() in Java SE 5.0

2008-04-30T00:43:00.000-07:00

Since getenv() method is no more deprecated in Java SE 5.0, we can start using this to get the System Environment variables. This method has two forms:

getenv() -> returns the Map contains the System Environment. NULL is returned if there are no System Environment varibales.
Ex: Map sysEnvMap = System.getenv();
String getenv(String key) -> returns the value of passed environment key. NULL is returned if the key does not exist.
Ex: String sysEnvStr = System.getenv("JAVA_HOME");

for more details: Java Tips

How to use Jar Tool

2008-04-30T00:42:00.000-07:00

You can package your classes in a jar file and that Jar file can be used in class path.

Following commands needs to be executed for various purposes in managing Jar files.

jar cf jar-file inputfiles: It is used to create new JAR.
jar tf jar-file: It is used to view all the files of the JAR.
jar xf jar-file: It is used to extract the JAR.
java -jar app.jar: It is used to run a JAR if the manifest file is present in the JAR. This manifest file contains the information of the file having main method. Content of the manifest is:
Main-Class: classname

for more details: Java Tips

How to use generics

2008-04-29T08:26:00.000-07:00

The 5.0 release of J2SE includes the first set of significant language-level changes to the Java platform in some time. In addition to new constructs for things such as the enhance for loop and variable argument lists, J2SE 5.0 provides compile-time type safety with the Java Collections framework through generics in accordance with JSR-14: Add Generic Types To The Java Programming Language.

One of the primary uses of generics is to abstract data types when working with collections. Prior to the JDK 5.0 release, when you created a Collection, you could put anything in it, for example:

    List myList = new ArrayList(10);
   myList.add(new Integer(10));
   myList.add("Hello, World");

If you wanted to restrict your Collection to a specific type, it was difficult at best. Getting items out of the collection required you to use a casting operation:

Integer myInt = (Integer)myList.iterator().next();

If you accidently cast the wrong type, the program would successfully compile, but an exception would be thrown at runtime. Unless you dealt specifically with everything in the Collection as an Object, casting typically happened blindly -- or by doing an instanceof check before calling the casted operation.

   Iterator listItor = myList.iterator();
  Object myObject = listItor.next();
  Integer myInt = null;
  if (myObject instanceof Integer) {
    myInt = (Integer)myObject;
  }

That situation underscores the beauty of generics. Generics allows you to specify, at compile-time, the types of objects you want to store in a Collection. Then when you add and get items from the list, the list already knows what types of objects are supposed to be acted on. So you don't need to cast anything. The "<>" characters are used to designate what type is to be stored. If the wrong type of data is provided, a compile-time exception is thrown. For example, if you try to compile the following class:

   import java.util.*;

  public class First {
    public static void main(String args[]) {
      List myList = new ArrayList(10);
      myList.add(10);
      myList.add("Hello, World");
    }
  }

you get an error like this:

   First.java:7: cannot find symbol
 symbol  : method add(java.lang.String)
 location: interface java.util.List
       myList.add("Hello, World");
               ^
 1 error

Here's the old way of looping through a List of String objects, that is, without generics and an enhanced for loop:

    import java.util.*;

   public class Old {
     public static void main(String args[]) {
       List list = Arrays.asList(args);
       Iterator itor = list.iterator();
       while (itor.hasNext()) {
         String element = (String)itor.next();
         System.out.println(element + " / " + element.length());
       }
     }
   }

If you compile and run the Old class and then run it with a string, like this:

   java Old Hello

you get:

   Hello / 5

With JDK 5.0, you can combine the new enhanced for loop construct with generics to create a program that is type-safe at compile-time, and is more readable and more maintainable. Here's what looping through a List of String objects looks like if you use generics and an enhanced for loop:

    import java.util.*;

   public class New {
     public static void main(String args[]) {
       List list = Arrays.asList(args);
       for (String element : list) {
         System.out.println(element + " / " + element.length());
       }
     }
   }

   java New Hello
 Hello / 5

As demonstrated here, generics and the enhanced for loop work well together.

For more information on generics, see:

For more details: Java Tips

How to use For Each loop

2008-04-29T08:19:00.000-07:00

JDK 5.0 provides a special kind of for loop for access through all the elements of it.

Syntax

For(vaiable : collection){ Statements; }

Example:

   int[] a={1,2,3,4,5,6,7,8,9,0};
  for(int i : a){
    System.out.println(i);
  }

For more details: Java Tips

How to pass unspecified number of arguments to a method

2008-04-29T08:17:00.000-07:00

JDK 5.0 provides a feature to pass unspecified number of argument to a method. Java treats the variable-length argument list as an array. This is represented by argument type followed by three dots in the declaration of the Method.

The method int sum(int…numbers) can take any number of parameters of type integer.

 public int sum(int...numbers) {

        int sum=0;
        for (int d : numbers )         
            sum =sum + d;
        return sum;
    }

    public static void main(String[] args) {
        int i=3;
        int j=6;
        int k=9;
        System.out.println("Sum  of two numbers"+sum(i,j));
        System.out.println("Sum of three number"+sum(i,j,k));
    }
}

For more details: Java Tips

How to launch a Unix script with Java

2008-04-29T08:14:00.000-07:00

You can use folowing code snippet to launch a Unix script with Java.

   String[] cmd = {"/bin/sh", "-c", "ls > hello"};
  Runtime.getRuntime().exec(cmd);

For more details: Java Tips

How to get free available memory in Java program

2008-04-29T08:13:00.000-07:00

This sample code will print the total and free memory at runtime to the console.

 public class MemoryExp {

    public static void main(String[] args) {
 
       System.out.println("Total Memory"+Runtime.getRuntime().totalMemory());    
       System.out.println("Free Memory"+Runtime.getRuntime().freeMemory());

    }
}

For more details: Java Tips

How to execute a command from code

2008-04-29T08:10:00.000-07:00

This Java tip illustrates a method of executing a command from the code. This is very helpful in cases when developer wants to execute some file (for ex. an exe) or run some command in a command prompt but without the interruption of the user.

 try {
    // Execute a command without arguments
    String command = "ls";
    Process child = Runtime.getRuntime().exec(command);
    
    // Execute a command with an argument
    command = "ls /tmp";
    child = Runtime.getRuntime().exec(command);
} catch (IOException e) {
}

// In case developer wants to execute a command with more than 
// one argument, it is necessary to use the overload that requires 
// the command and its arguments to be supplied in an array:

try {
    // Execute a command with an argument that contains a space
    String[] commands = new String[]{"grep", "hello world", "/tmp/f.txt"};
    
    commands = new String[]{"grep", "hello world", 
            "c:\\Documents and Settings\\f.txt"};
            
    Process child = Runtime.getRuntime().exec(commands);
    
} catch (IOException e) {
}

For more details: Java Tips

How to copy an array into another

2008-04-29T08:09:00.000-07:00

If the array only contains primitive types or if you want to copy only the object references, not duplicate the objects, then you can use the following method

 java.lang.System.arraycopy(Object src, int src_position,
  Object dst, int dst_position, int length);

Otherwise, if you want to duplicate the objects, you have to initialize your new array and write a loop that duplicates each object in the old array into the new one.

For more details: Java Tips

How do I find the list of all system properties

2008-04-29T08:01:00.000-07:00

You can use the following code snippet to obtain a list of all system properties:

   Enumeration list = System.getProperties().propertyNames();
  
  while(list.hasMoreElements()){
    System.out.println((String) list.nextElement());
  }

For more details: Java Tips

Create a Java source dynamically, compile and call

2008-04-29T07:59:00.000-07:00

The following wxample shows how to create a Java source code dynamically and then compile and run it.

 import java.io.*;
import java.util.*;
import java.lang.reflect.*;

public class MakeTodayClass {
  Date today = new Date();
  String todayMillis = Long.toString(today.getTime());
  String todayClass = "z_" + todayMillis;
  String todaySource = todayClass + ".java";
  
  public static void main (String args[]){
    MakeTodayClass mtc = new MakeTodayClass();
    mtc.createIt();
    if (mtc.compileIt()) {
       System.out.println("Running " + mtc.todayClass + ":\n\n");
       mtc.runIt();
       }
    else
       System.out.println(mtc.todaySource + " is bad.");
    }

  public void createIt() {
    try {
      FileWriter aWriter = new FileWriter(todaySource, true);
      aWriter.write("public class "+ todayClass + "{");
      aWriter.write(" public void doit() {");
      aWriter.write(" System.out.println(\""+todayMillis+"\");");
      aWriter.write(" }}\n");
      aWriter.flush();      
      aWriter.close();
      }
    catch(Exception e){
      e.printStackTrace();
      }
    }
  
  public boolean compileIt() {
    String [] source = { new String(todaySource)};
    ByteArrayOutputStream baos= new ByteArrayOutputStream();

    new sun.tools.javac.Main(baos,source[0]).compile(source);
    // if using JDK >= 1.3 then use
    //   public static int com.sun.tools.javac.Main.compile(source);    
    return (baos.toString().indexOf("error")==-1);
    }
    
  public void runIt() {
    try {
      Class params[] = {};
      Object paramsObj[] = {};
      Class thisClass = Class.forName(todayClass);
      Object iClass = thisClass.newInstance();
      Method thisMethod = thisClass.getDeclaredMethod("doit", params);
      thisMethod.invoke(iClass, paramsObj);
      }
    catch (Exception e) {
      e.printStackTrace();
      }
    }
 }

For more details: Java Tips

Creating Application Specific Exceptions

2008-04-29T07:57:00.000-07:00

When a program encounters an exceptional condition, it throws the exception like IOException, IllegalArgumentException etc.

Sometimes no standard class adequately represents the exceptional condition. In this condition programmer can choose to create his own exception class.

To create our own Exception existing type of exception are inherited, preferably one that is close in meaning to your new exception.

This code shows the use of user defined exception. In this code ApplicationException is user defined Exception.


public class ApplicationException extends Exception {

  private int intError;
  
  ApplicationException(int intErrNo){
    intError = intErrNo;
  }

  ApplicationException(String strMessage){
    super(strMessage);
   }

   public String toString(){
    return "ApplicationException["+intError+"]";
   }  
}

class ExceptionDemo{

  static void compute(int a) throws ApplicationException{

    System.out.println("called compute(" +a +" )");

    if(a>10){
      throw new ApplicationException(a);
    }

    System.out.println("NORMAL EXIT");
  }

  public static void main(String[] args) {

    try{
      compute(1);
      compute(20);

    }catch(ApplicationException e){
      System.out.println("caught " + e);
    }
  }
}

For more details: Java Tips

How can I force garbage collection to take place

2008-04-29T07:53:00.000-07:00

You can't force it but you call System.gc(), which is a "hint" to the

runtime engine that now might be a good time to run the GC. But garbage collection using this method is not guaranteed to be done immediately.

For more details: Java Tips

Tools to convert a program writen in C to Java

2008-04-29T07:44:00.000-07:00

There are tools which provides opportunity to translate C-code sources into Java classes. Some of them are listed below:

Jazillian: Jazillian is a tool that translates from C source code to Java source code. The Java code that it produces is highly maintainable: it looks like hand-written code.
C to Java converter: Some time ago I needed to convert one C program to Java. It is tedious and not interesting job to do. So I developed C to Java converter. I can not say, that it is fully functional or have no bugs. But you may find it useful to use this tool first, before making changes by hand.
C2J converter: C2J converter provides opportunity to translate C-code sources into Java classes.

for more details: Java Tips

Difference between String, StringBuffer and StringBuilder

2008-04-29T07:36:00.000-07:00

String is immutable whereas StringBuffer and StringBuilder can change their values.

The only difference between StringBuffer and StringBuilder is that StringBuilder is unsynchronized whereas StringBuffer is synchronized. So when the application needs to be run only in a single thread then it is better to use StringBuilder. StringBuilder is more efficient than StringBuffer.

Criteria to choose among String, StringBuffer and StringBuilder

1. If your text is not going to change use a string Class because a String object is immutable.
2. If your text can change and will only be accessed from a single thread, use a StringBuilder because StringBuilder is unsynchronized.
3. If your text can changes, and will be accessed from multiple threads, use a StringBuffer because StringBuffer is synchronous.

For details: Java Tips

Interesting Software Industry Quotes..........

2008-04-08T00:09:00.001-07:00

Read: Interesting Quotes

Interesting Software Industry Quotes..........

2008-04-08T00:09:00.000-07:00

Read: Interesting Quotes

Search Google like an expert

2008-04-08T00:07:00.000-07:00

Sunny's Blog: Search Google Like an expert

Correct way to handle JDBC connections

2008-03-28T05:58:00.000-07:00

Find out through the following url: http://mobidev.afrigis.co.za/?q=node/81

Java Vs Javascript

2008-03-28T05:55:00.000-07:00

The JavaScript programming language, developed by Netscape, Inc., is not part of the Java platform. The JavaScript programming language shares some attributes with the Java programming language, but it was developed separately.

For additional information about JavaScript, refer to the mozilla.org page titled What is JavaScript?

Differences among JDK, JRE & JVM

2008-03-28T05:52:00.000-07:00

The Java Virtual Machine (JVM) is not a standalone program. The JVM is part of the Sun Java 2 Runtime Environment, Standard Edition (JRE). Like a car needs an engine to run, the Sun JRE needs a virtual machine. You must download the entire JRE.

JDK includes JRE and other stand alone programs.

Configuring the Application Server

2008-03-28T02:14:00.000-07:00

Visit the following url:

http://docs.sun.com/app/docs/doc/819-3658/6n5s5nklb?a=view

Executing SQL Statements from a Sql File

2008-03-28T02:07:00.000-07:00

Use the follwoing command:

mysql> source file_name
or
mysql> \. exact_path_file_name

for an example:

mysql> \. /tmp/Marbil/marbil.sql

for further reading go to :
http://dev.mysql.com/doc/refman/5.0/en/batch-commands.html

How to check java version in your machine?

2008-03-28T01:25:00.000-07:00

in command prompt type
java -version

sjsas 9.0.1 installation in solaris spark 10 machine (64 bit)

2008-03-27T09:03:00.000-07:00

first uninstall previous version

1. go to the installtion directory (i installed in /opt/SUNWappserver )

use the following command:
./uninstall -console

installation:

1. download to a directory like /tmp/sjsas-9_1_01-solaris-sparc.bin

2. change the mode to the executable using the command:

chmod +x sjsas-9_1_01-solaris-sparc.bin

3. install in console mode

./sjsas-9_1_01-solaris-sparc.bin -console

mysql 5.1.23 installation in solaris spark 10 machine (64 bit)

2008-03-27T09:02:00.000-07:00

uninstallation:

check the package using the command:
pkginfo | grep mysql

previous installation using
pkgrm mysql

installation:

just follow the instruction : http://instmysql5sol10.blogspot.com/
(must create user and group)

post installation works have to be done by follwoing the website.

some mysql commands

1. show databases;
2. use mysql;
show tables;

Problems:
Root password have not set yet.

jdk 1.6 installation in solaris spark 10 machine (64 bit)

2008-03-27T08:28:00.000-07:00

remove all previous installation of jdk

## find out the all pkg of jdk using :
pkginfo | grep JDK

##then remove all listed.
using the command:
pkgrm SUNWj6rt SUNWj6dev SUNWj6cfg SUNWj6man SUNWj6dmo

Installation:

http://java.sun.com/javase/6/webnotes/install/jdk/install-solaris.html

unzip using the command:
zcat jdk-1_6_0-solaris-sparc.tar.Z | tar -xf -

1. first install 32 bit version jdk1.6
pkgadd -d . SUNWj6rt SUNWj6dev SUNWj6cfg SUNWj6man SUNWj6dmo

2. then install 64 bit version
pkgadd -d . SUNWj6rtx SUNWj6dvx SUNWj6dmx

also see the following url:
http://www.java.com/en/download/help/5000010700.xml

Javascript Cheat Sheet

2008-01-02T20:05:00.000-08:00

HTML Hide/Show Div

2008-01-01T22:17:00.001-08:00

function hideHTMLDiv(divId){

document.getElemenetById(divId).style.display = ‘none’;
}

function showHTMLDiv(divId){

document.getElemenetById(divId).style.display = ‘block’;
}

Java ClassPath

2008-01-01T19:53:00.000-08:00

In commandprompt write:

1. set classpath=D:\Mohiuddin;C:\Azad
2. for compiling classpath:

if you set classpath described above then u don't use cp otherwise use the follwing line:

javac -cp D:\Mohiuddin\servlet.jar;C:\Azad\vwp.jar azad.java

3. for running: java azad

Click to call in your mobile

2007-11-08T01:46:00.000-08:00

"<'a href="http://196.35.231.24/livtv/90.3gp">Show movie <'/a'>
<'a href="wtai://wp/mc;0835757424">Call Dulcie <'/a'>
"

Limit the resultset in MySQL

2007-09-27T04:32:00.000-07:00

You can limit the resultset of the database query by adding :

///**********************************************************
limit index, length
///**********************************************************

for example: select * from tblCustomers limit 0,10;
which shows the out put from the database only first 10 customers from 0 rows.

My Brief Introduction

2007-09-26T03:35:00.000-07:00

I am Mohammad Mohiuddin Azad from Dhaka, Bangladesh. I am currently enrolled as a P.hD. student in Computer Science at King Abdullah University of Science & Technology (KAUST).

I have passed my M.Sc. in KAUST also. Before that I have completed my Bachelor in Computer Science & Engineering (CSE) from Department of CSE, Bangladesh University of Engineering and Technology (BUET).

Before my admission to KAUST, I have worked for more than three (3) years in software industry as a software engineer.

I have worked in Structured Data Systems Limited (SDSL) from May, 2007 to November, 2009 as a software engineer. SDSL is a software development house that provides offshore software engineering solution services to small and medium sized software development companies and conforms to AS/NZS ISO 9001 and AS 3563 Quality Management Standards. It provides solution to the South African Client (Afrigis) to many of their developments. I have worked there in C#, Java, ASP.NET, JSP, Servlet, JSF, Visual Web Pack etc.

After that, I have worked in KB Group (UK) from December 2009 to July 2010 as a System Analyst and Software Developer. KB Group specialise in developing robust, proven information technology solutions for the entertainment and arts marketing sector. The KB Group eticketing solution is the online booking system market leader in the United Kingdom as it offers the most comprehensive functionality of any online ticketing system available. Our list of blue chip heritage attraction clients, including Buckingham Palace, Windsor Castle, Tate, Royal Academy of Arts, London Symphony Orchestra and the University of New Mexico, are testimony to the pedigree of our products. I have worked there in C++, ASP, VBScript, JavaScript, COM, HARU PDF API etc.

Javascript

2007-09-26T03:16:00.000-07:00

var elem = document.getElementById("id").
var elementInnerHTML = document.getElementById("id").innerHTML.