Introduction to NoSQL

NoSQL stands for NO SQL that is ,it does not follow traditional SQL with RDBMS instead it is a DBMS with support of large scalability and thus it is emerging as the solution to BigData.

Big data is a popular term used to describe the exponential growth and availability of data, both structured and unstructured.

Difference between NoSQL and SQL?

With increasing amount of data on social networking sites such as posts,tweets,messages etc.Need for fast data processing emerged SQL is strictly RDBMS and has strict Schema but it lacks in Scalability and that is where NoSQL emerges as a hero!

The key differences between them are:

Comparison on	SQL	NoSQL	Winner
Queries	Has good support for all kind of query needs like SELECT,UPDATE,JOINS etc.	Support is currently being added as it lacks the ease with which JOINS are performed in SQL and many other features of a   perfect SQL.	SQL
Speed	Uses query for performing tasks on data.	Uses Map Reduce to perform tasks on data which gives distinct advantage as Map Reduce computes parallel on blocks of a single file.	NoSQL
Transactions	Can commit any number of cross transactions.	Uses Entity Group for Multiple Row Transactions but usage of these Entity Groups for cross transactions is limited to 5 in most cases.	SQL
Scalability	Not scalable to millions of requests at a time.	More scalable than SQL as it uses multiple replication.	NoSQL
Schema	Strictly enforced schema which provides a good hold over how data is being stored and its relationship with others. But for huge table changing schema sometimes locks table temporary this is the main disadvantage.	No locking of table occurs.	NoSQL

To have more grasp on the differences between SQL and NoSQL please watch this video.

Now moving towards the BigData available solutions:-

1. The First Solution is developed and maintained by Google which is known as Data Store.
2. The Second Solution is known as Hadoop and is maintained by Apache.

Data Store

Developed and maintained by Google it is a stack which uses GFS(Google File System) as stroage file system and uses Big Table as NoSQL solution.

It's complete stack consists of :

Hadoop

Hadoop was initially developed at Yahoo and it is a set of tools which uses HDFS in place of GFS of Google and instead of BigTable it uses HBase.

To understand the working of Hadoop more clearly and broad sense.I would recommend you to read the following blog.

http://bradhedlund.com/2011/09/10/understanding-hadoop-clusters-and-the-network/

Adding JLabel and JButton to JTable

Adding JButton to JTable

First we are going to create a class which extends Cell Renderer.
ie.

public class Renderer extends DefaultTableCellRenderer{

        public Component getTableCellRendererComponent(JTable table, Object value, boolean isSelected,
         boolean hasFocus, int row, int column)
     {

        if(value instanceof JButton){
         
             JButton Button = (JButton)value;
           
           
            return (JButton)value;
        }
     
     

        else{
            return super.getTableCellRendererComponent(table, value, isSelected, hasFocus, row, column);
        }
     }
}


Then create a class MyModel which extends Default Table Model.

ie.

class MyModel extends javax.swing.table.DefaultTableModel{

    Object[][] row = new Object[2][2];

    Object[] col = {"File Name", "Status"};
   

    public MyModel (){
   
row[0][0]=new JButton("This File"); //adds button
row[0][1]="HI";
row[1][0]=new JButton("That File"); //adds button
row[1][1]="BYE"; //adds button
       
 }

       pack();
    //Adding columns
        for(Object c: col)
            this.addColumn(c);

    //Adding rows
        for(Object[] r: row)
            addRow(r);

    }

    @Override

    public Class getColumnClass(int columnIndex) {
        if(columnIndex == 1)return getValueAt(0, columnIndex).getClass(); //Sets JButton on 1 column
   
        else return super.getColumnClass(columnIndex);
   
         

    }

}

Now to get your table working add the following lines in your JFrame constructor.

jTable1.setModel(new MyModel());
 
 jTable1.setDefaultRenderer(JButton.class,  new Renderer());

Adding JLabel to JTable

First we are going to create a class which extends Cell Renderer.

ie.

public class Renderer extends DefaultTableCellRenderer{

 

        public Component getTableCellRendererComponent(JTable table, Object value, boolean isSelected,

         boolean hasFocus, int row, int column)

     {

 

        if(value instanceof JLabel){

           

             JLabel label = (JLabel)value;

            

             

            return (JLabel)value;

        }

       

       

 

        else{

            return super.getTableCellRendererComponent(table, value, isSelected, hasFocus, row, column);

        }

     }

}

Then create a class MyModel which extends Default Table Model.

ie.

class MyModel extends javax.swing.table.DefaultTableModel{

 

    Object[][] row = new Object[2][2];

    Object[] col = {"File Name", "Status"};

    

 

    public MyModel (){

    

row[0][0]=new JLabel("This File"); //adds label

row[0][1]="HI"; 

row[1][0]=new JLabel("That File"); //adds label

row[1][1]="BYE"; //adds label

         

 }

 

       pack();

    //Adding columns

        for(Object c: col)

            this.addColumn(c);

 

    //Adding rows

        for(Object[] r: row)

            addRow(r);

 

    }

 

    @Override

 

    public Class getColumnClass(int columnIndex) {

        if(columnIndex == 1)return getValueAt(0, columnIndex).getClass(); //Sets JLabel on 1 column

     

        else return super.getColumnClass(columnIndex);

    

          

 

    }

 

}

Now to get your table working add the following lines in your JFrame constructor.

jTable1.setModel(new MyModel());

   

 jTable1.setDefaultRenderer(JLabel.class,  new Renderer());

Introduction to Exceptions and Ducking

In this blog we are going to discuss about error and exception handling.


Note:It should be noted that only developers care about handling Exceptions although you must understand that you can handle Error using try-catch but it is useless as you cannot predict chance of occurring of an Error such as JAVA OutOfMemory.

The following diagram explains hierarchy order

Throwable is at top.
Two subclasses of it are Error and Exception.
We only deal with Exception excluding Runtime Exceptions.

Note:You can catch Error and Runtime Exceptions but it is advised not to as it is difficult to guess where and when they could occur.

 To deal with Exceptions you must remember this basic rule in JAVA that Exceptions must be declared or handled.

Exceptions are of two types.

 Checked Exceptions :

Include all subtypes of Exception, excluding classes that extend RuntimeException.
 Checked exceptions are subject to the handle or declare rule; any method that might throw a checked exception (including methods that invoke methods that can throw a checked exception) must either declare the exception using throws, or handle the exception with an appropriate try/catch.In case of Checked Exceptions compiler strictly follows handle or declare rule.


 Unchecked Exceptions :

Subtypes of Error or RuntimeException are unchecked, so the compiler doesn't enforce the handle or declare rule. You're free to handle them, or to declare them, but the compiler doesn't care one way or the other.


To deal with Exception and Error handling we use try-catch and finally blocks.

Basic definitions of try-catch and finally

try-Suspicious code is put within try block.
catch-contains code to executed for certain suspected Exceptions.
finally- code within it will be executed always whether exception occurs or not.


Sample code

import java.lang.Exception;
public class TestClass{
public static void main(String[] args)
{
try{
int d=5/0;
}
catch(Exception e) //Exception can catch any Exception but //always try be to specific
{
System.out.println(""+e.getMessage());  //This prints message if //any
}
finally{
System.out.println("Hello"); //This will run //always whether exception occured or not
}
}
}

Output will be 
/ by zero
Hello



Rules for try-catch block:
1.try must be followed either by catch or finally ,or both.
2.finally will be executed always whether exception occurs or not.
3.finally can only be interrupted by System.exit(0).
4.It is legal to throw exceptions in catch or finally block.
5.If multiple Exceptions are thrown then only Exception thrown at last is reported.



Ducking (or passing the buck !)
First consider the example below :

For point 5 of try-catch and ducking consider the following example:

import java.lang.Exception;
public class tilak{

public static void main(String[] args) throws Exception  //Exception is ducked till main
{
try{
tilak a=new tilak();
a.dos();
}
catch(Exception e){
throw new Exception("Hi");   //this is thrown second within catch block
}
finally{
throw new Exception("Hello");  //this is thrown last within finally block and it is reported
}
}
void dos() throws Exception{
throw new Exception("");    //this is thrown first within method
}

}

Output

Exception in thread "main" java.lang.Exception: Hello
at tilak.main(tilak.java:14)

You must be wondering why in the above example,I used public static void main(String[] args) throws Exception.
This is known as ducking as it is basic rule in java that Exception must be declared or handled.When you handle it then it is OK but when you declare it you say to caller that beware ! it can cause trouble.So what caller can do is either handle the trouble or pass it's trouble to it's own caller and like this each caller will pass the trouble to it's caller(ducking) and so on until passing reaches to main if main also passes it to jvm then program will shut.

Note: throw which we used in above example can only throw Throwable and it's subclasses.


Note :for a method throwing exceptions intentionally it's return type is useless.
Consider the following example.

import java.lang.Exception;
public class tilak{

public static void main(String[] args) throws Exception
{
try{
tilak a=new tilak();
a.dos();
}
catch(Exception e){
throw new Exception("Hi");
}

}
int dos() throws Exception{
return 0;
throw new Exception("");  //unreachable
}

}

OUTPUT
tilak.java:17: error: unreachable statement
throw new Exception("");
^
1 error


Consider this

import java.lang.Exception;
public class tilak{

public static void main(String[] args) throws Exception
{
try{
tilak a=new tilak();
a.dos();
}
catch(Exception e){
throw new Exception("Hi");
}

}
int dos() throws Exception{

throw new Exception("");
return 0;  //unreachable
}

}


OUTPUT

tilak.java:18: error: unreachable statement
return 0;
^
1 error