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Abstract Classes

Abstract classes and methods are introduced in PHP 5An abstract class is a class which will usually be used as a base class for other classes to inherit f

An abstract class is a class with or without data members that provides some functionality and lea

remaining functionality for its child class to implement.

The child class must provide the functionality not provided by the abstract class or else the child c

becomes abstract.

If a class contains abstract method then the class must be declared as abstract.

Any method which is declared as abstract must not have the implementation part but the declarati

The child classes which inherits the property of abstract base class, must define all the methods d

abstract.

Objects of an abstract and interface class cannot be created i.e. only objects of concrete class can

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To define a class as Abstract, the keyword abstract is to be used

abstract class Class_Name

{

// insert attribute definitions here

// insert method definitions here

}

The child classes which inherits the property of abstract base class, must define all the methods declared as abstr

An abstract method has no body

Example of Abstract Class

abstract class Furniture

{

private $height, width, length;

public function setData($h, $w, $l)

{

$this->height = $h;

$this->width = $w;

$this->length = $l;

}

//this function is declared as abstract and hence the function

//body will have to be provided in the child class

public abstract function getPrice();

}

class BookShelf extends Furniture

{

private $price;

public setData($h, $w, $l, $p)

{

parent::setData($h, $w, $l);

$this->price = $p;}

//this is the function body of the parent

public function getPrice()

{

return $this->price;

}

}

In the example, the method getPrice() in class Furniture has been declared as Abstract. Th

responsibility of the child class to provide the functionality of getPrice(). The BookShelf

Furniture class and hence provides the function body for getPrice().

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Private methods cannot be abstract :

An abstract class need not contain any abstract methods

On the other hand, if a class is not declared as abstract, it cannot contain any abstract methods

You can create a new abstract class that extends an earlier one

abstract class MyAbstractBaseClass

{

public abstract function doSomething();

}

abstract class MyAbstractSubClass extends MyAbstractBaseClass {}

Abstract classes ensure conformity because any classes derived from them must implement all ab

within the class. Attempting to forgo implementation of any abstract method defined in the class r

If a method is defined as abstract the

declared as private (it can only be publ

This is because a private method cann

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Characteristics of Abstract Classes

1. Single inheritance. Child classes can extend only one class at a time.

2. Abstract classes cannot be instantiated

3. Abstract classes can define class variables of type const only.

4. Abstract class A can be extended by another abstract class B. Abstract class B can implement

abstract functions in A.

5. In the previous case, a child class C which extends abstract class B must implement all abstra

well as the abstract functions in A which have not already been implemented in B.

6. The signature of the concrete functions and abstract functions must be the same.

7. The visibility of functions in the child classes must be the same or less restrictive than the pa

protected abstract function can be implemented as either protected or public but not private.

8. Declaring functions as static abstract throws a strict warning in PHP 5.2 or earlier, however, a

allowed.

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Characteristics of Abstract Classes

1. Single inheritance. Child classes can extend only one class at a time.

2. Abstract classes cannot be instantiated

3. Abstract classes can define class variables of type const only.

4. Abstract class A can be extended by another abstract class B. Abstract class B can implement

abstract functions in A.

5. In the previous case, a child class C which extends abstract class B must implement all abstra

well as the abstract functions in A which have not already been implemented in B.

6. The signature of the concrete functions and abstract functions must be the same.

7. The visibility of functions in the child classes must be the same or less restrictive than the pa

protected abstract function can be implemented as either protected or public but not private.

8. Declaring functions as static abstract throws a strict warning in PHP 5.2 or earlier, however, a

allowed.