Posts Tagged ‘oops’

C# Language Features OOPS .NET

Quick walkthrough on C# features.

DATA TYPES

Object Types: It is parent type of all other known types in .Net. If used as an argument in Method call then passing any type to method will cause late binding assignment to that argument.
Value and Reference Type: This type categorized on the storage of value in memory. Value Type are stored in Stack. e.g type INT, DOUBLE.
Reference types are stored in heap. e.g Type String and Object.
Converting value type into reference type called as Boxing and reverse is UnBoxing.

DECLARATION
C# allows simple and component variable declaration.

ENUMRATION
It is declared as set which are mapped to integers. This type allows us to have series which can have their mapping to unique integer value inside the set.

public enum EmployeeRole{ Trainee=0, Programmer=1, Sr Programmer=2}

 

Arrays: This type holds list.
e.g

int [] intArray;

 

OPERATORS Representing symbols for operations.
e.g Arithmetic[+, _, +], Logical[||, &&], String Concatenate[&], Increment and Decrement[+=], Comparison[<=, =>], Cast[()] etc..

FLOW CONTROL Controls the flow of your programme. e.g conditional statement [if ..else, switch], loops[while, do..while, for, foreach], functions.

CLASSES Class is type which includes all types, members, methods etc. It has visibility, its lifetime, relation, inheritance, method overloading..

REFLECTION Dynamically gather information of underlined type in late bound fashion. e.g Attributes allows to attach metadata to class and its members.

INTEROPERABILITY This feature facilitates to work with other programming language and API.
COM INTEROPERABILITY: This allows to integrate legacy components with .Net classes.
INVOKING WINDOWS API: This is same as VB6 feature to invoke and use windows API. Reference dll and create wrapper functions.

[sysimport(dll="user32.dll")]
private static extern int MessageBoxA(int hwind, string Message, string caption, int Type);

 

STRUCTURED ERROR HANDLING This is way of handling error by blocking code. e.g

Try
{}
Catch(){}
Finally{}

 

C# PREPROCESSOR This feature allows programmer to do better programming like expanding code, collapsing code…

Happy programming..

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Life Cycle Of A Servlet Explained Handling Servlet Life-Cycle Events Servlet Life Cycle Servlet Interview Questions Java Servlet Programming

Life Cycle Of A Servlet 

A servlet is a java code which runs at the server side to process request and return response to the client.

In other words, a servlet is an extension to the server which processes request and returns response as an HTML page to the client. Like applets we donot have main method in a servlet. As in case of applet,its life cycle is taken care by the browser itself,similarly in case of servlet its life cycle of a servlet is managed by the server/container.

 

Life Cycle Of A Servlet denotes the phases it goes through. These phases are symbolized by the life cycle methods in the servlet.As server manages the Life Cycle Of A Servlet, these life cycle methods are called by the server itself. Let us have a look at different Life Cycle methods Of A Servlet. These are as follows :

 

  1. init
  2. service
  3. destroy

 

1. init : The init method is the first Life Cycle method Of A Servlet. It is this method which after being called by the server makes a servlet eligible for being called a servlet. After the servlet class constructor is called,the init method is called by the server. The method looks like :

public void init(ServletConfig sc) throws ServletException {
  // Initialization code...
}

 

Here we can see that the ServletConfig object is passed to the init method. This object is created by serverand passed to the init method. Having received the ServletConfig object ,a servlet is said to be a servlet.

2. service : This life cycle method is called every time a request is sent to the servlet .This means that the servlet’s init method has been called and servlet is ready to process requests.This method looks like :

public void service(ServletRequest request,
                    ServletResponse response)
      throws ServletException, IOException{
}

3.destroy : This is the last phase in the Life Cycle Of A Servlet. Before the servlet object is garbage collected at the server side this method is called to relinquish the resources at the server side. This method looks like :

public void destroy() {
    // Finalization code...
  }

It can be noted that the init method is called only once in the Life Cycle Of A Servlet, service is called as many times as many the requests are fired and destroy is called only once in the Life Cycle Of A Servlet.

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Transaction Locking And Isolation In JDBC Transaction isolation levels Using Transactions JDBC Isolation Example JDBC Guide Basics Of JDBC

Transaction Locking And Isolation In JDBC

Transaction is a set of instructions which follow atomicity,consistency,Integrity and durability.

1. Atomicity : This states that either all actions should complete or none should occur.

2. Consistency : This imposes certain business rule.

3. Integrity : This states that the two actions shall not interfere with each other or access each others data.

4. Durability : This states that the changes occurred due to a certain action or transaction must be stored in a durable persistent storage.

 

When we talk about the Transaction Locking And Isolation In JDBC, following are the issues we need to address when to concurrent transactions are taking place :

1. Dirty read : This happens when uncommitted data is read.Typical example is :

a. Transaction 1 inserts a row into a table.

b.Transaction 2 reads the new row.

c.Transaction 1 rolls back.

2. Non-repeatable read : This happens when data reads from the same table for the same row are not same.Typical example is

a. Transaction 1 reads a row.

b. Transaction 2 updates the row.

c. Transaction 1 reads the same row a second time and gets a different  results.

 

3. Phantom Read : This occurs due to appearing of new records when same query is run at different times.Typical example is :

a. Transaction 1 reads all rows that satisfy a WHERE clause.

b. Transaction 2 inserts additional rows that satisfies the WHERE clause.

c. Transaction 1 executes  the WHERE condition and picks up the additional row.

There are different transaction isolation levels used from JDBC coding to address these issues.The function to set isolation level is :

 

con.setTranscationIsolationLevel(intvalue);

Different integer values can be provided as follows :

0 – JDBC_TRANSACTION_NONE
1 – JDBC_TRANSACTION_READ_UNCOMMITTED
2 – JDBC_TRANSACTION_READ_COMMITTED
4 – JDBC_TRANSACTION_REPEATABLE_READ
8 – JDBC_TRANSACTION_SERIALIZABLE

Once we set the isolation levels using the above function,we can address the issues of transaction level in JDBC connection.As the isolation     level increases it gets stricter and lower level problems are also addressed.If we have set the value to 8 ,the isolation level with value lesser than 8 ,ie. 0,1,2,4, are also taken  care of.

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