APEX : CONSTRUCTOR

Constructor

The constructor is a special method which has the following properties :

• Method name will be the same as a class.
• Access specifier will be public.
• This method will be invoked only once that is at the time of creating an object.
• This is used to instantiate the data members of the class.

For Example :

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public class TestObject

 {

   \\The no argument constructor

    public TestObject()

     {

       \\code

      }

  }

=================================================

There are 3 types of constructors:

• 1. Default Constructor
• 2. Non-parameterized Constructor
• 3. Parameterized Constructor 

1. Default Constructor

If an Apex Class doesn't contain any constructor then Apex compiler by default creates a dummy constructor on the name of the class when we create an object for the class.

For Example:
=================================================
public class Example
 {
  
  }
 Example e = new Example();

=================================================

In the above example, the apex class doesn't contain any constructor. So when we create an object for example class the Apex compiler creates a default constructor.

For Example:
=================================================
public example()
{

}
=================================================

2. Non-parameterized Constructor

• It is a constructor that doesn't have any parameters is called Non-parameterized constructor.
• Parameters are nothing but the values we are passing inside a constructor.

For Example:

=================================================

public class Example

{

  Integer number;

   String Name;

   public Example()  //Non-parametarized Constructor

   {

    number=10;

     name=Salesforcekid;

   }

}

=================================================

3. Parameterized Constructor 

• It is a constructor that has parameters.
• That means here we will take input from the user and then map it with our variable.

For Example:

=================================================

public class Example

 {

   Integer number;

   String Name;

public Example(Integer x, String myname) //Parametarized Constructor

 {

   number = x;

   Name = myname;

 }

=================================================

Now let's create an apex program to understand the use of constructor in an apex.

• Open developer console by clicking the org name on the Salesforce page.
• Click File --> New --> Apex Class.
• Enter the class name.
• Write the Apex Class.

For Example:

=================================================

public class Employee //Class

 {

   String EmployeeName;

   Integer EmployeeNo;

  

  public Employee() //Constructor

  {

    EmployeeName = 'Ajinkya';

    EmployeeNo = 10;

   }

 public void show() //Method

 {

   System.debug('Employee Name is '+ EmployeeName);

   System.debug('Employee No is '+ EmployeeNo);

  }

}

=================================================

Now open anonymous window and type this 

=================================================

Employee c1 = new Employee();

Employee c2 = new Employee();

c1.show();

c2.show();

=================================================

This will give you the following output

=================================================

EmployeeName is Ajinkya

EmployeeNo is 10

=================================================

Usage of Apex Program within Visualforce Page

When you want to call Apex class in visualforce page we have to declare our apex class in the following format.

=================================================

<apex:page Controller="ClassName">

=================================================

Whenever we call a visualforce page in which controller attribute is defined it will first create an object for the apex class which is defined in the controller.

You can call it a client-side controller.

When an object is created for the Apex class first it invokes the constructor.

WOHOOO.....You have just completed this Apex: Constructor episode.
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