{"id":101,"date":"2021-03-08T00:19:17","date_gmt":"2021-03-08T00:19:17","guid":{"rendered":"https:\/\/phptutorial.net\/?page_id=101"},"modified":"2025-04-07T11:22:27","modified_gmt":"2025-04-07T11:22:27","slug":"php-inheritance","status":"publish","type":"page","link":"https:\/\/www.phptutorial.net\/php-oop\/php-inheritance\/","title":{"rendered":"PHP Inheritance"},"content":{"rendered":"\n

Summary<\/strong>: in this tutorial, you will learn about the PHP inheritance that allows a class to reuse the code from another class.<\/p>\n\n\n\n

Introduction to the PHP inheritance #<\/a><\/h2>\n\n\n\n

Inheritance allows a class to reuse the code from another class<\/a> without duplicating it.<\/p>\n\n\n\n

In inheritance, you have a parent<\/strong> class with properties and methods, and a child<\/strong> class can use the code from the parent class.<\/p>\n\n\n\n

Inheritance allows you to write the code in the parent class and use it in both parent and child classes.<\/p>\n\n\n\n

The parent class is also called a base class or super class. And the child class is also known as a derived class or a subclass.<\/p>\n\n\n\n

To define a class inherits from another class, you use the extends<\/code> keyword.<\/p>\n\n\n\n

Suppose that you have a class called BankAccount<\/code> as follows:<\/p>\n\n\n

<?php<\/span>\n\nclass<\/span> BankAccount<\/span>\n<\/span>{\n    private<\/span> $balance;\n\n    public<\/span> function<\/span> getBalance<\/span>()<\/span>\n    <\/span>{\n        return<\/span> $this<\/span>->balance;\n    }\n\n    public<\/span> function<\/span> deposit<\/span>($amount)<\/span>\n    <\/span>{\n        if<\/span> ($amount > 0<\/span>) {\n            $this<\/span>->balance += $amount;\n        }\n\n        return<\/span> $this<\/span>;\n    }\n}<\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
The BankAccount<\/code> class has the private property $balance<\/code> and the public methods getBalance()<\/code> and deposit()<\/code>.<\/p>\n\n\n\n
To declare that the SavingAccount<\/code> inherits from the BankAccount<\/code>, you use the extends<\/code> keyword as follows:<\/p>\n\n\n
<?php<\/span>\n\nclass<\/span> SavingAccount<\/span> extends<\/span> BankAccount<\/span>\n<\/span>{\n}<\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
In this example, the SavingAccount<\/code> can reuse all the non-private properties and methods from the BankAccount<\/code> class.<\/p>\n\n\n\n
The following creates a new instance of the SavingAccount<\/code> class, calls the deposit()<\/code> method and shows the balance:<\/p>\n\n\n
<?php<\/span>\n\nrequire<\/span> 'SavingAccount.php'<\/span>;\n\n$account = new<\/span> SavingAccount();\n$account->deposit(100<\/span>);\necho<\/span> $account->getBalance();<\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
In this example, the SavingAccount<\/code> class reuses the properties and methods from the BankAccount<\/code> class.<\/p>\n\n\n\n
A child class can reuse properties and methods from the parent class. But the parent class cannot use properties and methods from the child class.<\/p>\n\n\n\n
Add properties and methods to the child class #<\/a><\/h2>\n\n\n\n
A child class can have its own properties and methods. In the following example, we add the $interestRate<\/code> property and setInterestRate()<\/code> method to the SavingAccount<\/code> class:<\/p>\n\n\n
<?php<\/span>\n\nclass<\/span> SavingAccount<\/span> extends<\/span> BankAccount<\/span>\n<\/span>{\n    private<\/span> $interestRate;\n\n    public<\/span> function<\/span> setInterestRate<\/span>($interestRate)<\/span>\n    <\/span>{\n        $this<\/span>->interestRate = $interestRate;\n    }\n}<\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
Call methods from the parent class #<\/a><\/h2>\n\n\n\n
To call a method from the parent class, you use the $this<\/a><\/code> keyword. <\/p>\n\n\n\n
The following example defines the addInterest()<\/code> method that calculates the interest and adds it to the balance:<\/p>\n\n\n
<?php<\/span>\n\nclass<\/span> SavingAccount<\/span> extends<\/span> BankAccount<\/span>\n<\/span>{\n    private<\/span> $interestRate;\n\n    public<\/span> function<\/span> setInterestRate<\/span>($interestRate)<\/span>\n    <\/span>{\n        $this<\/span>->interestRate = $interestRate;\n    }\n\n    public<\/span> function<\/span> addInterest<\/span>()<\/span>\n    <\/span>{\n        \/\/ calculate interest<\/span>\n        $interest = $this<\/span>->interestRate * $this<\/span>->getBalance();\n        \/\/ deposit interest to the balance<\/span>\n        $this<\/span>->deposit($interest);\n    }\n}<\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
In the addInterest()<\/code> method, we call the getBalance()<\/code> method from the BankAccount<\/code> class for calculating the interest and the deposit()<\/code> method to add the interest to the balance.<\/p>\n\n\n\n
Put it all together:<\/p>\n\n\n
<?php<\/span>\n\nclass<\/span> BankAccount<\/span>\n<\/span>{\n    private<\/span> $balance;\n\n    public<\/span> function<\/span> getBalance<\/span>()<\/span>\n    <\/span>{\n        return<\/span> $this<\/span>->balance;\n    }\n\n    public<\/span> function<\/span> deposit<\/span>($amount)<\/span>\n    <\/span>{\n        if<\/span> ($amount > 0<\/span>) {\n            $this<\/span>->balance += $amount;\n        }\n\n        return<\/span> $this<\/span>;\n    }\n}\n\nclass<\/span> SavingAccount<\/span> extends<\/span> BankAccount<\/span>\n<\/span>{\n    private<\/span> $interestRate;\n\n    public<\/span> function<\/span> setInterestRate<\/span>($interestRate)<\/span>\n    <\/span>{\n        $this<\/span>->interestRate = $interestRate;\n    }\n\n    public<\/span> function<\/span> addInterest<\/span>()<\/span>\n    <\/span>{\n        \/\/ calculate interest<\/span>\n        $interest = $this<\/span>->interestRate * $this<\/span>->getBalance();\n        \/\/ deposit interest to the balance<\/span>\n        $this<\/span>->deposit($interest);\n    }\n}\n\n$account = new<\/span> SavingAccount();\n$account->deposit(100<\/span>);\n\/\/ set interest rate<\/span>\n$account->setInterestRate(0.05<\/span>);\n$account->addInterest();\necho<\/span> $account->getBalance();<\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
Inhertiance and UML #<\/a><\/h2>\n\n\n\n
You use the open arrow from the child class to the parent class to represent the inheritance relationship. The following UML diagram shows the inheritance relationship between the BankAccount<\/code> and SavingAccount<\/code> classes:<\/p>\n\n\n
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\"\"<\/figure>\n<\/div>\n\n\n
Summary #<\/a><\/h2>\n\n\n\n
    \n
  • Inheritance allows a class to reuse the code of another class without duplicating it.<\/li>\n\n\n\n
  • Use the extends<\/code> keyword to define one class that inherits from another class.<\/li>\n\n\n\n
  • A class that inherits another class is called a subclass, a child class, or a derived class. The class from which the subclass inherits is a parent class, a superclass, or a base class.<\/li>\n\n\n\n
  • A subclass can have its own properties and methods.<\/li>\n\n\n\n
  • Use $this<\/code> keyword to call the methods of the parent class from methods in the child class.<\/li>\n<\/ul>\n
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