A fully object-oriented language means everything is represented as an object but can’t differentiate between primitive types and objects of classes but C# is not purely object oriented since it supports many procedural programming concepts such as pointers to an extent. An object is a basic unit of Object Oriented Programming and represents the real-life entities. A typical C# program creates many objects, which as you know, interact by invoking methods. We can Create objects in C# in the following ways:
1) Using the ‘new’ operator: A class is a reference type and at the run time, any object of the reference type is assigned a null value unless it is declared using the new operator. The new operator assigns space in the memory to the object only during run time which means the allocation is dynamic.
Syntax:
// The className() is a call // to the constructor className ObjectName = new className();
Note: The constructor can be a default constructor or a user-defined one.
Example:
// C# Program to show the use // of the new Operator using System;
namespace NewOperator {
class Rectangle {
public int length, breadth;
// Parameterized Constructor
// User defined
public Rectangle( int l, int b)
{
length = l;
breadth = b;
}
// Method to Calculate Area
// of the rectangle
public int Area()
{
return length * breadth;
}
} // Driver Class class Program {
// Main Method
static void Main( string [] args)
{
// Creating an object using 'new'
// Calling the parameterized constructor
// With parameters 10 and 12
Rectangle rect1 = new Rectangle(10, 12);
// To display are of the Rectangle
int area = rect1.Area();
Console.WriteLine( "The area of the" +
" Rectangle is " + area);
}
} } |
The area of the Rectangle is 120
2) Creating Reference to Existing Object: The reference can be declared only with the class name and reference name. The reference cannot exist independently. It has to be assigned to an already existing object of the same class. Any changes made in the reference will be saved to the object it is referring to. It is kind of like an alias.
Syntax:
className RefName; RefName = objectName;
Example:
// C# Program to show the use // of references using System;
namespace Reference {
class Triangle {
public int side, altitude;
// Not defining a constructor
// Method to calculate area
// of the Triangle
public double Area()
{
return ( double )0.5 * side * altitude;
}
} // Driver Class class Program {
// Main Method
static void Main( string [] args)
{
// Creating an object using new
// calls the default constructor
Triangle tri1 = new Triangle();
// Only creates a reference of
// type Triangle
Triangle tri2;
// Displaying area of tri1
Console.WriteLine( "Area of tri1 is "
+ tri1.Area());
// Assigns the reference to tri1
tri2 = tri1;
// Making changes in tri2
tri2.side = 5;
tri2.altitude = 7;
// Displaying area of tri1
// Changes made in the reference tri2
// are reflected in tri1 also
Console.WriteLine( "Area of tri1 is "
+ tri1.Area());
}
} } |
Area of tri1 is 0 Area of tri1 is 17.5
3) Creating an Array of objects: If you need the multiple numbers of objects of the same class you can create an array of objects. This will require you to declare the array first and then initialize each element { object in this case }. You can use for loop for initialization.
Syntax:
className[] arrayName = new className[size];
// C# Program to illustrate how to // create the array of objects using System;
namespace ArrayofObjects {
class Circle {
public int radius;
// Defining Constructor
public Circle()
{
radius = 0;
}
// Method to set value of radius
public void setValue( int r)
{
radius = r;
}
// Method to calculate the
// area of the Circle
public double Area()
{
return ( double )3.14 * radius * radius;
}
} // Driver Class class Program {
// Main Method
static void Main( string [] args)
{
// To declare an array of two objects
Circle[] circleArray = new Circle[2];
// Initialize the objects
circleArray[0] = new Circle();
circleArray[1] = new Circle();
// to set values for the radius
circleArray[0].setValue(1);
circleArray[1].setValue(2);
// for loop to display areas
for ( int i = 0; i < circleArray.Length; i++)
{
Console.Write( "Area of circle with radius " + (i + 1));
Console.Write( " is " + circleArray[i].Area() + "\n" );
}
}
} } |
Area of circle with radius 1 is 3.14 Area of circle with radius 2 is 12.56