Create an Object using New Operator: Java

New operator is used to create a new object of an existing class and associate the object with a variable that names it. Basically new operator instantiates a class by allocating memory for a new object and returning reference to that memory.

Every class needs an object to use its member and methods by other classes. Programmer have to create that object using new operator to use functionality provided by that class. Following is the syntax to create new object of an existing class:

Class_variable =new Class_Name();

This syntax basically describes some points about new operator as below:

• Allocates memory to class_variable for new object of class.
• It invokes object constructor.
• Requires only single postfix argument which calls to constructor.
• Returns reference to memory which is usually assigned to variable of appropriate type.

Following statement will create an object of city class and allocate memory to this newly created object:

City metro;

metro = new City();

The equivalent code for the above statement that can be written in single line is:

City metro = new City();

So new operator does two things overall i.e. it first allocates memory somewhere to hold an instance of the type, and then calls a constructor to initialize an instance of the type in that newly allocated memory.

After creating new object for a class, that object can use all the members and methods defined in that class. You can assign all the properties for that class and operate available or new functions on those properties.

Managing indexes with pre-defined Query: SQL Server

In addition to creating indexes in sql server, database developer also need to maintain them to ensure their continued optimal performance. The common index maintenance tasks include disabling, enabling, renaming, and dropping an index. As a database developer, you need to regularly monitor the performance of the index and optimize it.

Disabling Indexes

When an index is disabled, the user is not able to access the index. If a clustered index is disabled then the table data is not accessible to the user. However, the data still remains in the table, but is unavailable for Data Modification Language (DML) operations until the index is dropped or rebuilt.

To rebuild and enable a disabled index, use the ALTER INDEX REBUILD statement or the CREATE INDEX WITH DROP_EXISTING statement.

The following query disables a non-clustered index, IX_EmployeeID, on the Employee table.

ALTER INDEX IX_EmployeeID
ON Employee DISABLE

Enabling Indexes

After an index is disabled, it remains in the disabled state until it is rebuilt or dropped. You can enable a disabled index by rebuilding it through one of the following methods:

• Using the ALTER INDEX statement with the REBUILD clause
• Using the CREATE INDEX statement with the DROP_EXISTING clause
• Using the DBCC DBREINDEX

By using one of the preceding statements, the index is rebuilt and the index status is set to enable. You can rebuild a disabled clustered index, when the ONLINE option is set to ON.

Renaming Indexes

You can rename the current index with the help of the sp_rename system stored procedure.
The following statement renames the IX_JobCandidate_EmployeeID index on the JobCandidate table to IX_EmployeeID.

EXEC sp_rename
‘HumanResources.JobCandidate.IX_JobCandidate_EmployeeID’,
‘IX_EmployeeID’, ‘index’

Dropping Indexes

When you no longer need an index, you can remove it from a database. You cannot drop an index used by either a PRIMARY KEY or UNIQUE constraint, except by dropping the constraint.

The following statement drops the IDX_Employee_ManagerID index on the Employee table:

DROP INDEX IDX_Employee_ManagerID
ON Employee

How to Create Partition Scheme and Clustered Index: SQL Server

After creating the partition function, programmer needs to create a partition scheme to associate it with the partition function. Based on the boundary values defined in the partition function, there will be five partitions. The data of each partition is stored in a filegroup. You should have the same number of filegroups as partitions. If there are five partitions, you need to create five filegroups: fg1, fg2, fg3, fg4, fg5.

The following statements create the PSOrderDate partition scheme, associating it with the PFOrderDate partition function:

CREATE PARTITION SCHEME PSOrderDate
AS PARTITION PFOrderDate
TO (fg1, fg2, fg3, fg4, fg5)

The partition scheme, PSOrderDate, created in the preceding statement directs each partition to a separate filegroup.

Creating a Clustered Index

After creating the partition scheme, you need to associate it with a clustered index. As the clustered index is created on the attribute having unique and non-null values, you can create the index on the SalesOrderID column of the SalesOrderHeader table. To create the partitioned index, you need to associate the clustered index with the partition scheme as follows:

CREATE CLUSTERED INDEX ix_SalesOrderID
ON Sales.MySalesOrderHeader (SalesOrderID)
ON PSOrderDate (OrderDate)

The preceding statement will distribute the table data into five filegroups based on the yearly data of orders stored in the OrderDate column.

How to Create Partitioned Indexes in SQL Server

In SQL Server, indexes can also be partitioned based on the value ranges. Similar to the partitioned tables, the partitioned indexes also improve query performance. Partitioning enables you to manage and access subsets of data quickly and efficiently. When indexes become very large, you can partition the data into smaller, more manageable sections as the data is spread across file groups in a database.

Consider an example. In the Adventure Works database, the SalesOrderHeader table contains the details about the order received by Adventure Works, Inc. As the data in this table is large, the query takes a long time to execute. To solve this problem, you can create a partitioned index on the table. Partitioning an index will distribute the data in the table into multiple filegroups, thereby partitioning the table. This will enable the database engine to read or write data quickly. This also helps in maintaining the data efficiently.

Partitioning is allowed only in the Enterprise Edition of SQL Server. To create a partitioned index, you need to perform the following tasks:

• Create a partition function
• Create a partition scheme.
• Create a clustered index.

Creating a Partition Function

Similar to creating a partitioned table, you need to create a partition function to create a partitioned index. The partition function will determine the boundary values for creating partitions.

Consider an example. The queries on the SalesOrderHeader table are mostly base on the OrderData column. The sales manager of Adventure Works requires the details of the orders received, on a yearly basis. The table contains the details of orders for the last five years beginning from 2001. Based on this information, you can create a partition function as follows:

CREATE PARTITION FUNCTION PFOrderDate (date time)
AS RANGE RIGHT FOR VALUES (‘2002-01-01’, ‘2003-01-01’, ‘2004-01-01’, ‘2005-01-01’)

The preceding statement creates a partition function, PFOrderDate, by using the date time data type. It specifies four boundary values. Therefore, there will be five partitions. As range right is specified for partitioning, the first partition will contain data less than the first boundary value, 2002-01-01. The second partition will contain data greater than or equal to 2002-01-01 and less than or equal to 2003-01-01. Similarly, other partitions will store data.

How to Retrieve XML Data Using XQuery

In addition to FOR XML, SQL Server allows programmer to extract data stored in variables or columns with the XML data type by using XQuery. XQuery is a language that uses a set of statements and functions provided by the XML data type to extract data. As compared to the FOR XML clause of the SELECT statement, the XQuery statements allow you to extract specific parts of the XML data.

Each XQuery statement consists of two parts, prolog and body. In the prolog section, you declare the namespaces. In addition, schemas can be imported in the prolog. The body parts specifies the XML nodes to be retrieved. The XQuery language includes the following statements:

• For: Used to iterate through a set of nodes at the same level as in an XML document.
• Let: Used to declare variables and assign values.
• Order by: Used to specify a sequence.
• Where: Used to specify criteria for the data to be extracted.
• Return: Used to specify the XML returned from a statement.

The XQuery statements also use the following functions provided by the XML data type:

Query: Used to extract XML from an XML data type. The XML to be retrieved is bicycle is manufactured at AdventureWorks, it passes through a series of work centre locations. Each work centre location produces a different cycle component. Therefore, the number of production steps varies between different work centres.

To analyse the production process, the management of AdventureWorks needs to retrieve a list of the location IDs of all the work centers, which have more than four steps. You need to generate the list displaying the location ids in the ascending order of the steps included in the work centres.

To perform this task, the database developer can create the following query:

SELECT Instructons.query
(‘ declare namespace
ns=http://schemas.microsoft.com/sqlserver/2004/07/adventure-works/ProductModelManuInstructions:
for $work in /ns:root/ns:Location
where count(#work/ns:step) > 4
order by count ($work/ns:step)
return
count($work/ns:step)’) AS Result
FROM Production.ProductModel
WHERE Instructions IS NOT NULL

Value: Used to return a single value from an XML document. To extract a single value, you need to specify an XQuery expression that identifies a single node and a data type of the value to be retrieved.

For example, the management of AventureWorks, Ins. Wants a list containing the product model id, product name, machine hours, and labour hours. However, not all product have production instructions. As a database developer, you have stored this data in the XML format in the ProductModel table. You can create the following query to display the results:

SELECT ProductModelID, Name, Instructions.value (‘declare namespace ns=”http//schemas.microsoft.com/sqlserver/2004/07/adventure-works/ProductManuInstructions”;
(/ns:root/ns:Location/@LaborHours) [1]’, ‘float’)AS
LaborHours,
Instructions.value(declare namespace
Ns=”http://schemas.microsoft.com/sqlserver/2004/07/adventure-works/ProductModelManuInstructions”;
(/ns:root/ns:Location/@MachineHours) [1]’, ‘float’) AS MachineHours
FROM Production.ProductModel
WHERE Instructions IS NOT NULL

Exist: Used to check the existence of a node in an XML data. The function returns I if the specified node exists else it returns 0. For example, the management of AdventureWorks, wants the details of all the customers in the city ‘NJ’. The details of all the customers are stored in an XML format in the CustDetails table. You can use the following query to display the results:

SELECT Cust_ID, Cust_Details.exist
(‘Customer[@City=’NJ”]’) AS ‘True’ FROM CustDetails

Retrieve XML data from DataSet

How to Define Methods with Behavior: Java

Objects have behavior that is implemented by its methods. Other objects can ask an object to do something by invoking its methods. This section tells you everything you need to know about writing methods for your Java classes.

In Java, you define a class’s methods in the body of the class for which the method implements some behavior. Typically, you declare a class’s methods after its variables in the class body although this is not required.

Implementing Methods

Similar to a class implementation, a method implementation consists of two parts: the method declaration and the method body

methodDeclaration {
        methodBody
}

The Method Declaration

At minimum, a method declaration has a name and a return type indicating the data type of the value returned by the method:

returnType methodName( ) {
. . .
}

This method declaration is very basic. Methods have many other attributes such as arguments, access control, and so on.

Objects as Instances of Class

A class defines only a blueprint and its concrete version comes into effect only through objects that implement the functionality as defined by class. Recall our class example of City class. The objects created from this class will have two variables: name and population; and they will be able to represent cities. The object of City class will also have a method namely display ( ). An object of a class is typically named by a variable of the class type. For example, the program CityTrial in Example 4.7 declares the two variables metl1 and metro2 to be of type City, as follows;

City metro1, metro2;

This gives us variables of the class City, but so far there are no objects of the class. Objects are class value that are named by the variables. To obtain an object you must use the new operator to create a “new” object. For example, the following creates an object of the class City and names it with the variable metro1:

Metro = new city ( );

For now you need not go into details, simply note that the statement like:

Class-variable = new class-Name ( );

Creates a new object of the specified class and associates it with the class type variables. Since the class variable now names an object of the class, we will often refer to the class variable as an object of the class. (This is really the same usage as when we refer to an int variable n as “the integer n”, even though the integer is strictly speaking not n but the value of n.)

Unlike what we did in previous lines, the declaration of a class type variable and the creation of the object are more typically combined into one statement as follows:
City metro1 = new City( );

To instantiate an object, Java uses the keyword new.

Declare member variables in JAVA

How to Declare Member Variables in Classes: JAVA

A class’s state is represented by its member variables. You declare a class’s member variables in the body of the class. Typically, programmer declare a class’s variables before you declare its methods, although this is not required.

classDeclaration {
        member variable declarations
        method declarations
}

To declare variables that are members of a class, the declarations must be within the class body, but not within the body of a method. Variables declared within the body of a method are local to that method i.e., available and accessible only inside the method.

Types

• Class variable (static variable): A data member that is declared once for a class. All objects of the class type, share these data members, as there is single copy of them available in memory. The class variables are declared by adding keyword static in front of a variable declaration.
• Instance variable: A data member that is created for every object of the class. For example, if there are 10 objects of a class type, there would be 10 copies of instance variables, one each for an object.

Consider the following code.

Public class sample {
        int anInt; // instance variable
        float aFloat; // instance variable
        static float anotherFloat; // class variable
};

Suppose there are five objects created for class type Sample. Then there would be five copies of variables anInt and aFloat but there would be one copy of variable anotherFloat which all five objects can share.

Notice that class variables are declared by adding a keyword static before the variable declaration. Keyword static in the variable declaration makes it class variable.

Method are similar: your classes can have instance methods and class methods. Instance methods operate on the current object’s instance variables but also have access to the class variables. Class methods (also called static methods), on the other hand, cannot access the instance variables declared within the class (unless they create a new object and access them through the object). Also, class methods can be invoked on the class, you don’t need an instance to call a class method.

A class method can be invoked by:

• Just its name within its own class e.g., check( ).
• Class-name.method-name outside its class e.g., Sample.check ( )

In above two lines, we assume that method check( ) is a static method in class Sample.

Implement Object-Oriented in JAVA

How to Declare Classes with Members: JAVA

In order to bring a class into existence in Java program, it should be declared. A class is declared using keyword class. The generic syntax for class declaration in Java is:

Class   <class_name>
{
    Statements defining class come here
}
The angle-brackets < > mean these names are to be provided by the programmer and [ ] brackets mean, this part is optional. The class name must be provided while declaring a class. This is used to refer to the class whenever an instance (the object) of the class is created. The class name must be a legal identifier in Java. While naming classes, generally nouns are used and the first letter is given in uppercase e.g., City or Date etc. the curly brackets { } mark the beginning of a class and/or a method. The curly brackets are also used to specify block statements.

A class is a blueprint or prototype that you can use to create many objects. The implementation of a class is comprised of two components: the class declaration and the class body.

classDeclaration   {
    // classBody
}

When a class is declared, no memory space is allotted to it. This is because a class is simply a blueprint or logical placeholder containing objects and method. Memory space is allocated when objects of a class type are created.

The Class Declaration

The class declaration component declares the name of the class along with other attributes such as whether the class is public or not.

The Class Body

The class body follows the class declaration and is embedded with in curly braces ‘{‘ and ‘}’. The class body contains declaration for all instance variable and class variable (known collectively as member variable) for the class. In addition, the class body contains declarations and implementations for all instance methods and class methods (known collectively as methods) for the class. The following template shows the form of a class definition that is most commonly used; however, it is legal to intermix the method definitions and the instance variable declaration.

Public class class_Name    {
Instance_Variable_Declaration_1
Instance_Variable_Declaration_2
. . . . . .
Instance_Variable_Declaration_Last
Method_Definition_1
Method_Definition_2
     . . . . .
    Method_Definition_Last
}