PHP inheritance lets one class extend another with extends. The child class receives the parent’s public and protected members, can replace or augment inherited methods, and must call the parent constructor explicitly when it defines its own constructor. A PHP class can extend only one parent class.
What inheritance means in PHP
Inheritance models an “is-a” relationship. A specialized class reuses and refines a more general class: a SavingsAccount is an Account, for example.
Declare the relationship with extends:
<?php
class Account
{
public function label(): string
{
return 'Account';
}
}
class SavingsAccount extends Account
{
public function interestRate(): float
{
return 0.03;
}
}
$account = new SavingsAccount();
echo $account->label(); // Account
echo $account->interestRate(); // 0.03SavingsAccount defines its own method and also uses the inherited public label() method. The official PHP Object Inheritance documentation describes this parent-child relationship.
What a child class inherits
A subclass inherits the parent class’s public and protected methods, properties and constants. Visibility still controls where each member can be used.
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| Member visibility | Accessible from the child? | Meaning |
|---|---|---|
public |
Yes | Available wherever public access is permitted. |
protected |
Yes | Available inside the declaring class and its subclasses. |
private |
No | Available only inside the class that declared it. |
Private parent members are not child-accessible members. If a parent needs to expose an operation to subclasses, use a protected method or provide a suitable public or protected method. See the current PHP visibility reference for the complete rules.
Overriding a parent method with parent::
A child can define a method with the same name as an inherited method and specialize its behavior. This is called overriding. Use parent::methodName() to run the parent implementation from the override, typically when the child should add to rather than discard the original behavior.
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<?php
class Notification
{
public function send(string $message): string
{
return "Sending: $message";
}
}
class EmailNotification extends Notification
{
public function send(string $message): string
{
return "Email: " . parent::send($message);
}
}
echo (new EmailNotification())->send('Hello');
// Email: Sending: HelloEmailNotification is still a Notification, but its version of send() adds an email-specific prefix and delegates the original work to the parent. Overriding can also replace the parent behavior entirely when that is the intended design.
Visibility and constructor chaining
When a child declares its own __construct(), PHP does not automatically run the parent constructor. Call parent::__construct(...) explicitly whenever the parent must initialize its state. If the child declares no constructor, the parent constructor may be inherited.
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<?php
class Account
{
public function __construct(protected string $owner) {}
protected function ownerLabel(): string
{
return $this->owner;
}
}
class SavingsAccount extends Account
{
public function __construct(string $owner, private float $rate)
{
parent::__construct($owner);
}
public function summary(): string
{
return $this->ownerLabel() . ' — rate ' . $this->rate;
}
}
echo (new SavingsAccount('Mina', 0.03))->summary();Here the parent owns the protected $owner property and ownerLabel(); the child can use both. The child owns its private $rate property. The promoted-property syntax in this example requires a PHP version that supports constructor property promotion and typed properties; adapt the declarations if you support an older PHP release. The constructor rule is documented in Constructors and Destructors.
PHP supports one parent class
Each class can extend only one class. This is valid:
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class Account {}
class SavingsAccount extends Account {}
class PremiumSavingsAccount extends SavingsAccount {}This is not valid PHP:
class Child extends ParentA, ParentB {} // invalidInheritance can form a multilevel chain, but it cannot combine two independent parent classes. The PHP basics documentation states that a class can inherit from only one base class.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Inheritance, interfaces and traits: which mechanism fits?
Inheritance is not the only way to share design or behavior. Choose based on the relationship you need:
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| Mechanism | Best fit | What it provides | Key constraint |
|---|---|---|---|
| Class inheritance | A genuine specialization or “is-a” relationship | Inherited public and protected implementation, properties and constants | One parent class per child |
| Interface | Unrelated classes that must follow the same contract | Required method signatures; a class may implement several interfaces | It is a contract, not a parent carrying implementation in the same way |
| Trait | Composing reusable methods into classes | Behavior inserted into a class without creating a parent-child hierarchy | It does not create an “is-a” relationship |
Read the official Object Interfaces documentation and Classes and Objects overview for the language definitions. Use inheritance when the subtype really is a form of the parent; use an interface when several otherwise unrelated classes need the same contract; use a trait when you need to compose implementation without coupling classes into one hierarchy.
Common inheritance mistakes
- Trying to access a private parent property or method: private visibility belongs only to the class that declared the member. Expose a protected or public operation instead.
- Assuming the parent constructor always runs: a child constructor must call
parent::__construct()when parent initialization is required. - Attempting multiple class inheritance: PHP allows one parent class, not a comma-separated list of parents. Combine interfaces or traits when those are the actual requirements.
- Overriding without deciding whether to preserve parent behavior: call
parent::method()when the parent work remains part of the operation; otherwise implement the replacement deliberately. - Using inheritance only for convenient code reuse: a hierarchy creates coupling. If there is no real specialization relationship, an interface, trait or another composition approach may communicate the design more accurately.
A practical checklist
- Identify the “is-a” relationship and name the general parent class.
- Declare the child with
class Child extends Parent. - Keep members that subclasses need as
protectedor expose controlled methods; do not expect children to read private parent state. - Override only the behavior that needs specialization, and use
parent::method()when the original behavior should remain. - If the child has a constructor, call
parent::__construct()with the required arguments. - For multiple capabilities, evaluate interfaces and traits instead of trying to extend more than one class.
Reference documentation
The relevant PHP Manual pages are Object Inheritance, The Basics, Visibility, Constructors and Destructors, Object Interfaces and the Classes and Objects overview.
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