Type Conversion and its Types used in JAVA

An implicit type conversion is a conversion performed by the compiler without programmer’s intervention. An implicit conversion is applied generally whenever differing data types are intermixed in an expression (mixed mode expression), so as not to lose information.

The Java compiler converts all operands up to the type of the largest operand, which is called type promotion. This is done operation by operation, as described in the following type conversion rules
If either operand is of type double, the other is converted to double.

• Otherwise, if either operand is of type float, the other is converted to float.
• Otherwise, if either operand is of type long, the other is converted to long.
• Otherwise, both operands are converted to type int.

Once these conversion rules have been applied, each pair of operands is of same type and the result of each operation is the same as the type of both operands.

The implicit type conversion wherein datatypes are promoted is known as Coercion.

Although coercion exempts the user from worrying about different datatype of operands, yet it has one disadvantage. Coercions decrease the type error detection ability of the compiler. You have already used the implicit type conversion unknowingly. Recall that you use “ “ + <number> (e.g., “ “ +5) to convert it to string.

Explicit type conversion

An explicit type conversion is user-defined that forces an expression to be specific type. The explicit conversion of an operand to a specific Type Casting. Type casting in Java is done as shown below :

(type) expression Where type is a valid Java data type to which the conversion is to be done. For example, to make sure that the expression (x + y/2) evaluates to type float, write it as: (float) (x +y /2)

Casts are often considered as operators. As an operators, a cast is unary and has the same precedence as any other unary operator.

Below is a table that indicates to which of the other primitive types a given primitive data type can be cast. The symbol C indicates that an explicit cast is required since the precision is decreasing. The symbol A indicates that the precision is increasing so an automatic cast occurs without the need for an explicit cast. N indicates that the conversion is not allowed.

The * asterisk indicates that the least significant digits, may be lost in the conversion even though the target type allows for bigger numbers. For example, a large value in an int type value that uses all 32 bits will lose some of the lower bits when converted to float since the exponent uses 8 bits of the 32 provided for float value.

Assigning a value to a type with a greater range (e.g. from short to long) poses no problem, however, assigning a value of larger data type to a smaller data type (e.g., from double to float) may result in losing some precision.

Programmer cannot typecast a Boolean type to another primitive type and viceversa. So, we cannot cast a primitive type to an object reference, or viceversa.  

Expression and its types

Expressions and its types used in JAVA

An expressions is composed of one or more operations. The objects of the operation(s) are referred to as operands. The operations are represented by operators. Therefore, operators, constants, and variables are the constituents of expressions.

An Expression in Java is any valid combination of operators, constants, and variables are the constituents of Java tokens. The expression in Java can be of any type

• Arithmetic expression
• Compound expression
• Relational (or logical) expression

Type of operators used in an expression determine the expression type. For instance, if an expression is formed using arithmetic operator, it is an arithmetic expression; if an expression has relational and/or Boolean operators, it is a Boolean expression. An arithmetic expression always results in a number (integer or real) and a logical expression always results in a logical value i.e., either true or false.

Arithmetic Expressions

Arithmetic expressions can either be pure integer expressions or pure real expressions. Sometimes a mixed expression can also be formed which is a mixture of real and integer expressions.

In pure expressions, all the operands are of same type. And in mixed expressions, the operands are of mixed or different data types.

Integer expressions are formed by connecting integer constants and/or integer variables using integer arithmetic operators.  The following are valid integer expression:

final int count = 30
int I, J, K, X, Y, Z
– J, K – X, K + X – Y + count, – J + K * Y, J/Z, Z % X

Real expression are formed by connecting real constants and/or real variables using real arithmetic operators. The following are valid real expression:

final float bal = 250.3f:
float qty, amount value;
double fin, inter;

Rule for these arithmetic expressions is the same and it states that:
An arithmetic expression may contain just one numeric variable or a constant, or it may have two or more variables or/and constants, or two or more expressions joined by valid arithmetic operators. Two or more variables or operators should not occur in continuation.

Apart from variables, constants and arithmetic operators, an arithmetic expression may consist of Java’s mathematical functions that are part of Java standard library and are available through Math class defined in java.lang package. The following image lists various math functions that are defined in the Math class of Java.lang package.

You can use these math functions as per following syntax:
Math.Function_name (argument list) ---- The arguments are the values required by a function to work upon. For example, to calculate ab, you may write: math.pow(a, b)

Following are examples of valid arithmetic expressions :
Given     int a, b, c ;  float, p, q, r ; double x, y, z ;
a/b, p/q +a-c, x/y + p*a/b, Math .sqrt (b)*a) – c, Math.ceil (p) + a)/c, Math. Max (c,b) +x/y – z/q +c  

Following are example of invalid arithmetic expressions :
Given int , a, b, c ;  float, p, q, r ;   double x, y, z ;
x + * r      two operators on continuation.
q(a + b – z/4)   operator missing between q and parenthesis.
Math.pow (0, - 1)  Domain error because if base = 0 then exp should not be <= 0.
n *log (-3) + p/q  Domain error because logarithm of negative number is not possible.

How to Update Data in tables: SQL

Programmer need to modify the data in the database when the specifications of a customer, a client, a transaction, or any other data maintained by the organization undergo a change.

For example, if a client changes his address or if the quantity of a product ordered is changed, the required changes need to be made to the respective rows in the tables. You can use the UPDATE statement to make the changes. Updating ensures that the latest and correct information is available at any point of time. One column of a row is the smallest unit of an update.

You can update data in a table by using the UPDATE DML statement. The syntax of the UPDATE statement is:

UPDATE table_name SET column_name = value [, column_name = value]
[FROM table_name]
[WHERE condition]
Where,

• Table_name specifies the name of the table you have to modify.
• Column_name specifies the columns you have to modify in the specified table.
• Value specifies the value(s) with which you have to update the column(s) of the table. Some valid values include an expression, a column name, and a variable name. The DEFAULT and NULL keywords can also be supplied.
• FROM table_name specifies the table(s) that is used in the UPDATE statement.
• Condition specifies the rows that you have to update.

Guidelines for Updating Data

You need to consider the following guidelines while updating data:

• An update can be done on only one table at a time.
• If an update violates integrity constraints, then the entire update is rolled back.

The following statement updates the AddressLine2 attribute of AddressID 104

UPDATE Address
SET AddressLine2 = ‘Plaza Palace’
WHERE AddressID = 104

Consider another example where you need to update the Title of an employee, Lynn Tsoflias to ‘Sales Executive’, in the Employee table. To perform this task, you need to refer to the contact table to obtain the Contact ID. You can update the details by using the following statement:

UPDATE HumanResources.Employee SET Title = ‘Sales Executive’
FROM HumanResources.Employee e, Person.Contact c
WHERE e.contactID = c.ContactID
AND c.FirstName = ‘Lynn’ and c.LastName = ‘Tsoflias’

When the preceding command is executed, the Title will be changed to ‘Sales Executive’.

Delete data from database and related table.

How to Delete Data from Table or Related Table, SQL

Programmer need to delete data from the database when it is no longer required. The smallest unit that can be deleted from a database is a row. You can delete a row from a table by using the DELETE DML statement. The syntax of the DELETE statement is:

DELETE [FROM] table_name
[FROM table (s)]
[WHERE condition]
Where,

• Table_name specifies the name of the table from which you have to delete rows.
• Table_name specifies the name of the table(s) required to set the condition for deletion.
• Condition specifies the condition that identifies the row(s) to be deleted.

For example, the following statement deletes the address details of AddressID 104 from the Address table:

DELETE Address
WHERE AddressID = ‘104’

Deleting Data from Related Tables

While deleting records form related tables, you need to ensure that you first delete the records from the table that contain the foreign key and then from the table that contains the primary key.

Consider the example of the Adventure Works. The Employee table contains data of those employees who have retired from the company. This data is not required anymore. This increases the size of the database.

You are required to ensure that this old data is removed from the Employee table. You can delete this data by using the following SQL statement:

DELETE FROM HumanResources.Employee
WHERE BirthDate < dateadd (yy, -60, getdate ())

The database contains tables related to the Employee table. The related tables are HumanResources.EmployeeAddress, HumanResources.EmployeeDepartmentHistory, HumanResources.EmployeePayHistory, and HumanResources.JobCandidate. The EmployeeID attribute in these tables is a foreign key to the EmployeeID attribute of the Employee table. Therefore, the query results in an error. Therefore, you need to delete data from the related tables before executing the preceding DELETE statement.

Deleting All the Records from a Table

As a database developer, you might need to delete all the records from a table. You can do this by using the following DELETE statement:

DELETE table_name

You can also use the TRUNCATE DML statement. The syntax of the TRUNCATE statement is:
TRUNCATE TABLE table_name
Where,

• Table_name specifies the name of the table from which you have to delete rows. However, TRUNCATE TABLE is executed faster.

TRUNCATE TABLE does not support the WHERE clause. In addition, the TRUNCATE TABLE statement does no fire a trigger. When truncate is used, the deleted rows are not entered in the transaction log.

For example, the following statement deletes all the records from the Address table:
TRANCATE TABLE Address

Manipulate XML Data and Parsing with XML document.

How to Manipulate XML data in Database Table, SQL

With a growth in clients accessing data through heterogeneous hardware and software platforms, a need across for a language that could be interpreted by any environment. This resulted in the evolution of a language called XML. SML is a mark-up language that is used to describe the structure of data in a standard hierarchical manner.

The structure of the documents containing the data is described with the help of tags contained in the document. Therefore, various business applications store their data in XML documents.

SQL Server allows you to save or retrieve data in the XML format. This enables the SQL Server to provide database support to various kinds of applications. As a database developer, it is important for you to learn to manipulate the XML data by using SQL Server.

The structure of the XML data can be defined in the form of a supporting Document Type Definition (DTD) or schema. You can read more about XML in the appendix.

Staring XML Data in a Table

The XML data is available in the form of XML fragments or complete XML documents. An XML fragment contains XML data without a top-level element that contains the complete data.

SQL Server 2005 uses XML as a data type to save the XML data in its original state. You can create tables or variables by using this data type to store the XML data. However, you can also shred the XML data and store the values in different columns in a rowset. This process of transforming the XML data into a rowset is called as shredding.

In SQL Server, you can store the XML data in the following ways:

• A rowset
• An XML column

Staring the XML Data in a Rowset

Consider an example. You have received the order details from a vendor. The order details are generated by the application used by the vendor in an XML document. You need to store this data in a database table. For this, you need to shred the XML data. The SQL Server allows you to shred the XML data by using the OPENXML function and its related stored procedures.

Shredding an XML document involves the following tasks:

• Parse the XML document.
• Retrieve a rowset from the tree.
• Store the data from the rowset.
• Clear the memory.

How to Parse XML Document and Retrieve Rowset: SQL Server Syntax

SQL Server provides the sp_sml_preparedocument stored procedure to parse the XML document. This stored procedure reads the XML document and parses it with the MSXML parser. Parsing an XML document involves validating the XML data with the structure defined in the DTD or schema.

The parsed document is an internal tree representation of various nodes in the XML document, such as elements, attributes, text, and comments. Sp_xml_preparedocument returns a handle or pointer that can be used to access the newly created internal representation of the XML document. This handle is valid for the duration of the session or until the handle is invalidated by executing

Sp_xml_removedocument.

Retrieving a Rowset from the Tree

After verifying the accuracy of the structure and completeness of data, you need to extract the data from the available XML data. For this, you can use the openxml function to generate an in-memory rowset from the parsed data. The syntax of the openxml function is:

Openxml ( idoc int [ in] , rowpattern nvarchar [ in ] , [ flags byte [ in ] ] )
[ WITH ( SchemaDeclaration | TableName ) ]
Where,

• Idoc specifies the document handle of the internal tree representation of an XML document.
• Rowpattern specifies the XPath pattern used to identify the nodes (in the XML document whose handle is passed in the idoc parameter) to be processed as rows.
• Flags indicates the mapping that should be used between the XML data and the relational rowset, and how the spill-over column should be filled. Flags is an optional parameter and can have the following values:
  0 – to use the default mapping (attributes)
  1 – to retrieve attribute values
  2 – to retrieve element values
  3 – to retrieve both attribute and element values
• Schemadeclaration specifies the rowset schema declaration for the columns to be returned by using a combination of column names, data types, and patterns.
• TableName specifies the table name that can be given, instead of SchemaDeclaration, if a table with desired schema already exists and no column patterns are required.

C# - Basic Syntax

C# supports object-oriented features like Class, Object, Encapsulation, Polymorphism, Data abstraction, Inheritance etc. In Object-Oriented Programming technology, we works on real time entity(known as object), these entity related to each other also communicate by message passing. If we discuss about class, a class consists of data member and member function (known as encapsulation). Using Object we can call method also initialize class data members. In later session we will discuss about object oriented features. In this article we will design basic structure of class and object.For example, let us consider a circle object. It has attributes like radius. Depending upon the design, it may need ways for accepting the values of this attribute, calculating area and display details.

Let us look at an implementation of a circle class and discuss C# basic syntax, on the basis of our observations in it:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace circle
{
    class circle_area
    {
         private static float pi = 3.14F;
         private int radius;
        // initialize datamember in the constructor.
         public circle_area(int radi)
         {
             radius = radi;

         }
        // calcuate area of the circle.
         public double getarea()
         {
             return pi * radius * radius;
         }

    }
    class Program
    {
        static void Main(string[] args)
        {
            circle_area ca = new circle_area(5);
            Console.WriteLine(Convert.ToString(ca.getarea()));
            Console.ReadKey();
        }
    }
}


When the above code is compiled and executed, it produces the following result:

The First line of the program define the system Namespace, a single program can hold multiple using statement. The System Namespace consists of many class like Console class. The Second line of the program hold NameSpace declaration, according to my previous article a single Namespace can contain multiple classes, in this program we have two class first one is circle_area and second one is program. In later session we will discuss, how a Namespace consists of another Namespace, deligates and structure. The third line of the program define class declaration, In this program we have two classes and each class hold at least single member function.

Comments in C#

Comments are used for designing user friendly program. Compilers ignore the comment entries. we can use single line as well as multi-line comments in the c# program The multi-line comments in C# programs start with /* and terminates with the characters */ as shown below:

/* Program define how to

calculate circle area with static keyword*/

Single-line comments are declared by double slash like //, according to above mentioned code, which is

// initialize Data Member in the constructor.

Data Member

It shows the properties of an object, suppose you have a object employee so create a class, which covers employee details like Employee_id, Employee_Name, etc. These properties known as data members. In this example we have two properties for circle class, these are pi and radius. Basically these variable are used for storing data.

Member Functions

It shows the behavior of the class, in which we can perform some action related to object properties. In this example we have one member function getarea(), which returns calculated area in double type.

Class and how to declare it:

Class is a user defined data type or you can say it is a composite data type. we have many definition of a class like "Class is a container of data member and member function" and second one is "class is a instance of a variable". 

Design a new class in c#- synatx of class

class class_name 

{

// Data member;

// Member function;    

}

Ok, Now understand what is in this program:

First start with main () method because its the entry point of the program. Here we have a object , which is created by new keyword. Also assign the instance name , which is ca. According to constructor theory, When we create a object ,constructor call automatically. Assign the Data Member by the constructor.  

 After assign the data member we can perform some operation on it. Now, we calculate area of the circle using getarea() method. This method is called from object ca.