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Describe the differences between an Interface and an Abstract Class in php.
Describe the differences between an Interface and an Abstract Class in php.
Jul 08, 2025 am 01:40 AM
Interfaces define behavioral specifications, and abstract classes provide partial implementations. The interface only defines methods but does not implement them (PHP 8.0 can be implemented by default), supports multiple inheritance, and methods must be public; abstract classes can contain abstract and concrete methods, support single inheritance, and members can be protected or public. Interfaces are used to unify behavioral standards, realize polymorphism, and multiple inheritance; abstract classes are used to encapsulate public logic and share partial implementations. Selection basis: Use interfaces when you need to flexibly define behaviors, and use abstract classes when you need to share logic.
In PHP, both interfaces and abstract classes are used to implement abstract concepts in object-oriented design, but their usage scenarios and functions are significantly different. Simply put, interfaces define behavioral norms, while abstract classes are more like incomplete class templates.
The interface defines "what can be done"
Interfaces only care about the definition of methods, and do not involve specific implementations. You can think of it as a contract: as long as a class implements this interface, all the methods inside must be implemented.
interface Animal {
public function makeSound();
} Any class that implements the Animal interface must provide a specific implementation of makeSound() method.
Common usage:
- Define a unified standard of behavior
- Implement polymorphism
- Support multiple inheritance (one class can implement multiple interfaces)
Note:
- There is no implementation code in the interface (PHP 8.0 allows default implementation)
- All methods must be public
- Constants can be defined
Abstract classes are more like "semi-finished categories"
An abstract class is a class that cannot be instantiated and usually contains some implemented methods and some unimplemented abstract methods. It is more suitable for use when multiple subclasses share part of the logic, but have parts of their own implementations.
abstract class Animal {
abstract public function makeSound();
public function sleep() {
echo "Zzz...";
}
} Subclasses must implement makeSound() , but they can directly use sleep() method of the parent class.
Common usage:
- Provide partial implementation
- Encapsulate public logic
- Control subclass structure
Note:
- There can be abstract methods and concrete methods
- Constructors and attributes can exist
- Subclasses can only inherit one abstract class
Summary of key differences
| characteristic | interface | Abstract Class |
|---|---|---|
| Method implementation | Not allowed (except the default method) | There can be specific implementation |
| Inheritance method | Multiple interfaces | Single inheritance |
| Member access permissions | Must be public | Can be protected or public |
| Is it instantiable | no | no |
| Is it possible to define attributes | PHP 8.1 supports constants | Can have attributes |
In general, when you only need to define a set of behavioral specifications and want multiple classes to be flexible, choose an interface; and when you have a set of related classes that need to share some common logic, abstract classes will be more suitable.
Basically all of them. Although they look a bit similar, the difference is quite obvious when used.
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