Understanding abstract classes and methods in PHP - Abstract class PHP example

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Abstract classes and methods in PHP serve as a foundational structure for other classes to be built upon. They are used to outline a common interface for related classes, without implementing the full functionality themselves. This concept is crucial in object-oriented programming, as it promotes a high level of abstraction and design flexibility. To illustrate how abstract classes and methods can be effectively used in PHP, let's explore a practical example involving a bank account system.

Abstract Class Definition

In our example, we have an abstract class named BankAccount which defines the basic structure of a bank account. It includes three abstract methods: balance, deposit, and withdraw. These methods are declared but not implemented within the BankAccount class because the specifics of these operations might vary depending on the type of bank account.

<?php 

abstract class BankAccount { 
    
   abstract public function balance();
   abstract public function deposit($amount);
   abstract public function withdraw($amount);
   
}  

?>
    

Concrete Class Implementation

We then extend this abstract class with a concrete class called SavingAccount, which implements the abstract methods defined in BankAccount. The SavingAccount class is responsible for managing the balance of a savings account, including functionality to check the balance, deposit money, and withdraw money, adhering to the constraints specified in the BankAccount class.

<?php 

class SavingAccount extends BankAccount { 
    
   private $balance = 0;

   public function __construct($balance) { 
      $this->balance = $balance;
   }
   
   public function balance() { 
      return $this->balance;
   } 
   
   public function deposit($amount) { 
      $this->balance += $amount;
   } 
   
   public function withdraw($amount) { 
      if($this->balance > $amount) { 
         $this->balance -= $amount;
      } else { 
         echo "Insufficient balance";
      }
   } 
}

?>
    

This example showcases the power of abstract classes and methods in establishing a clear and consistent interface for similar classes. By defining a common set of operations in an abstract class, we can ensure that all subclasses, such as SavingAccount, adhere to a specific contract, promoting code reuse and modularity.

FAQs

What is an abstract class in PHP?

An abstract class in PHP is a class that cannot be instantiated on its own and is designed to be a base class for other classes. It can contain abstract methods, which are methods declared in the abstract class but must be implemented by its child classes.

Why use abstract classes?

Abstract classes are used to create a common interface for a group of classes. They allow you to define methods that must be implemented by any subclass, ensuring that all subclasses adhere to a particular contract. This is useful for establishing a consistent structure while allowing for flexibility in how each subclass implements the details.

Can an abstract class have non-abstract methods?

Yes, an abstract class can have non-abstract methods. These are methods with their implementations defined in the abstract class itself. Subclasses inheriting from the abstract class can use these methods as-is or override them if necessary.

What is the difference between an abstract class and an interface in PHP?

The main difference between an abstract class and an interface in PHP is that an abstract class can contain both abstract methods (which do not have a body) and concrete methods (which have an implementation), while an interface can only contain abstract methods. Additionally, a class can inherit from only one abstract class but can implement multiple interfaces.

Can abstract classes have constructors in PHP?

Yes, abstract classes can have constructors in PHP. While the abstract class itself cannot be instantiated, its constructor can be called from a subclass's constructor to initialize properties defined in the abstract class.

How do you declare an abstract method?

An abstract method is declared with the `abstract` keyword followed by a method signature without a body. For example: abstract public function myFunction($arg);. The implementation of this method must be provided by the child class.

Can you instantiate an abstract class directly?

No, you cannot instantiate an abstract class directly. Attempting to do so will result in a fatal error. Abstract classes are designed to be extended by other classes that implement the abstract methods defined within them.

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