Object Oriented Concepts

Question 1

Class −

Answer 1

This is a programmer-defined data type, which includes local functions as well as local data. You can think of a class as a template for making many instances of the same kind (or class) of object.

Question 2

Class −

Answer 2

This is a programmer-defined data type, which includes local functions as well as local data. You can think of a class as a template for making many instances of the same kind (or class) of object.

Question 3

Object −

Answer 3

An individual instance of the data structure defined by a class. You define a class once and then make many objects that belong to it. Objects are also known as instance.

Question 4

Member Variable −

Answer 4

These are the variables defined inside a class. This data will be invisible to the outside of the class and can be accessed via member functions. These variables are called attribute of the object once an object is created.

Question 5

Member function

Answer 5

− These are the function defined inside a class and are used to access object data.

Question 6

Inheritance −

Answer 6

When a class is defined by inheriting existing function of a parent class then it is called inheritance. Here child class will inherit all or few member functions and variables of a parent class.

Question 7

Parent class −

Answer 7

A class that is inherited from by another class. 
This is also called a base class or super class.

Question 8

Child Class

Answer 8

A class that inherits from another class. 
This is also called a subclass or derived class.

Question 9

What is Polymorphism

Answer 9

This is an object oriented concept where same function can be used for different purposes.
For example function name will remain same but it make take different number of arguments and can do different task.

Question 10

Overloading −

Answer 10

a type of polymorphism in which some or all of operators have different implementations depending on the types of their arguments. Similarly functions can also be overloaded with different implementation.

Question 11

Data Abstraction

Answer 11

Any representation of data in which the implementation details are hidden (abstracted).

Question 12

Encapsulation

Answer 12

Refers to a concept where we encapsulate all the data and member functions together to form an object.

Question 13

Constructor

Answer 13

− refers to a special type of function which will be called automatically whenever there is an object formation from a class.

Question 14

Destructor −

Answer 14

Refers to a special type of function which will be called automatically whenever an object is deleted or goes out of scope.

Question 15

Class definition

Question 16

Object −

Answer 16

An individual instance of the data structure defined by a class. You define a class once and then make many objects that belong to it. Objects are also known as instance.

Question 17

Member Variable −

Answer 17

These are the variables defined inside a class. This data will be invisible to the outside of the class and can be accessed via member functions. These variables are called attribute of the object once an object is created.

Question 18

Member function

Answer 18

− These are the function defined inside a class and are used to access object data.

Question 19

Inheritance −

Answer 19

When a class is defined by inheriting existing function of a parent class then it is called inheritance. Here child class will inherit all or few member functions and variables of a parent class.

Question 20

Parent class −

Answer 20

A class that is inherited from by another class. 
This is also called a base class or super class.

Question 21

Child Class

Answer 21

A class that inherits from another class. 
This is also called a subclass or derived class.

Question 22

What is Polymorphism

Answer 22

This is an object oriented concept where same function can be used for different purposes.
For example function name will remain same but it make take different number of arguments and can do different task.

Question 23

Overloading −

Answer 23

a type of polymorphism in which some or all of operators have different implementations depending on the types of their arguments. Similarly functions can also be overloaded with different implementation.

Question 24

Data Abstraction

Answer 24

Any representation of data in which the implementation details are hidden (abstracted).

Question 25

Encapsulation

Answer 25

Refers to a concept where we encapsulate all the data and member functions together to form an object.

Question 26

Constructor

Answer 26

− refers to a special type of function which will be called automatically whenever there is an object formation from a class.

Question 27

Destructor −

Answer 27

Refers to a special type of function which will be called automatically whenever an object is deleted or goes out of scope.

Question 28

Class definition

Question 29

Here is an example which defines a class of Books type −

Answer 29

price = $par;
}

      function getPrice(){
         echo $this->price ."<br>";
      }

      function setTitle($par){
         $this->title = $par;
      }

      function getTitle(){
         echo $this->title ." <br>";
      }
   }
?>

Question 30

Creating Objects in PHP

Answer 30

Following is an example of how to create object using new operator.

$physics = new Books;
$maths = new Books;
$chemistry = new Books;

Question 31

Calling Member Functions

Answer 31

$physics->setTitle( “Physics for High School” );
$chemistry->setTitle( “Advanced Chemistry” );
$maths->setTitle( “Algebra” );

$physics->setPrice( 10 );
$chemistry->setPrice( 15 );
$maths->setPrice( 7 );

Question 32

What is a Constructor Functions

Answer 32

Constructor Functions are special type of functions which are called automatically whenever an object is created. So we take full advantage of this behaviour, by initializing many things through constructor functions.

Question 33

How do you define a Constructor Function

Answer 33

function __construct( $par1, $par2 ) {
$this->title = $par1;
$this->price = $par2;
}

Question 34

Use constructor function

Answer 34

$physics = new Books( "Physics for High School", 10 );
$maths = new Books ( "Advanced Chemistry", 15 );
$chemistry = new Books ("Algebra", 7 );

/* Get those set values */
$physics->getTitle();
$chemistry->getTitle();
$maths->getTitle();

$physics->getPrice();
$chemistry->getPrice();
$maths->getPrice();

Question 35

Destructor

Answer 35

Like a constructor function you can define a destructor function using function __destruct(). You can release all the resources with-in a destructor.

Question 36

Public Members

Answer 36

Unless you specify otherwise, properties and methods of a class are public. That is to say, they may be accessed in three possible situations −

From outside the class in which it is declared

From within the class in which it is declared

From within another class that implements the class in which it is declared

Question 37

Private members

Answer 37

By designating a member private, you limit its accessibility to the class in which it is declared. The private member cannot be referred to from classes that inherit the class in which it is declared and cannot be accessed from outside the class.

A class member can be made private by using private keyword infront of the member.

Question 38

A class member can be made private by using private keyword infront of the member.

Answer 38

class MyClass {
   private $car = "skoda";
   $driver = "SRK";

   function \_\_construct($par) {
      // Statements here run every time
      // an instance of the class
      // is created.
   }

   function myPublicFunction() {
      return("I'm visible!");
   }

private function myPrivateFunction() {
return(“I’m not visible outside!”);
}
}

Question 39

Protected members

Answer 39

A protected property or method is accessible in the class in which it is declared, as well as in classes that extend that class. Protected members are not available outside of those two kinds of classes. A class member can be made protected by using protected keyword in front of the member.

Question 40

Here is different version of MyClass

Answer 40

class MyClass {
   protected $car = "skoda";
   $driver = "SRK";

   function \_\_construct($par) {
      // Statements here run every time
      // an instance of the class
      // is created.
   }

   function myPublicFunction() {
      return("I'm visible!");
   }

protected function myPrivateFunction() {
return(“I’m visible in child class!”);
}
}

Question 41

Interfaces

Answer 41

Interfaces are defined to provide a common function names to the implementers.
Different implementors can implement those interfaces according to their requirements.
You can say, interfaces are skeletons which are implemented by developers.

Question 42

Interfaces

Answer 42

interface Mail {
public function sendMail();
}

Then, if another class implemented that interface, like this

class Report implements Mail {
   // sendMail() Definition goes here
}

Question 43

Constants

Answer 43

A constant is somewhat like a variable, in that it holds a value, but is really more like a function because a constant is immutable. Once you declare a constant, it does not change.

Question 44

Declaring one constant is easy, as is done in this version of MyClass

Answer 44

class MyClass {
   const requiredMargin = 1.7;

   function \_\_construct($incomingValue) {
      // Statements here run every time
      // an instance of the class
      // is created.
   }
}

Question 45

Abstract Classes

Answer 45

An abstract class is one that cannot be instantiated, only inherited. You declare an abstract class with the keyword abstract, like this

Question 46

When inheriting from an abstract class, all methods marked abstract in the parent’s class declaration must be defined by the child; additionally, these methods must be defined with the same visibility.

Answer 46

abstract class MyAbstractClass {
   abstract function myAbstractFunction() {
   }
}

Question 47

Static Keyword

Answer 47

Declaring class members or methods as static makes them accessible without needing an instantiation of the class. A member declared as static can not be accessed with an instantiated class object (though a static method can).

Question 48

Static Keyword try out following example

Answer 48

staticValue() . “\n”;

?>