What is the difference between interfaces and abstract classes in PHP?

Interfaces and abstract classes are used to create extensible PHP code, and there is the following key difference between them: Interfaces enforce through implementation, while abstract classes enforce through inheritance. Interfaces cannot contain concrete methods, while abstract classes can. A class can implement multiple interfaces, but can only inherit from one abstract class. Interfaces cannot be instantiated, but abstract classes can.

Interfaces vs. Abstract Classes in PHP: An In-Depth Comparison

Introduction

Interfaces and abstract classes are powerful tools in PHP for creating extensible and modular code. However, when choosing which one to choose, it is crucial to understand the differences between them. This article will delve into the key features of interfaces and abstract classes and illustrate their differences through practical examples.

Interface

The interface defines a method contract. A class that implements an interface must implement all declared methods but cannot provide their implementations. Interfaces only define method signatures and do not provide any implementation details.

Syntax:

interface IExample {
    public function doSomething();
}

Abstract class

An abstract class is a partially implemented class that contains abstract methods and concrete method. Abstract methods must be implemented by subclasses derived from the abstract class. Abstract classes provide shared implementation and behavior but still allow subclasses to customize specific methods.

Syntax:

abstract class Example {
    public function doSomething() {
        // 具体实现
    }

    abstract public function doSomethingElse();
}

Key differences

• Implementation: Interface is implemented by enforced, while abstract classes are enforced through inheritance.
• Concrete methods: Interfaces cannot contain concrete methods, but abstract classes can.
• Multiple inheritance: A class can implement multiple interfaces, but can only inherit from one abstract class.
• Instantiability: Interfaces cannot be instantiated, but abstract classes can.

Practical Case

Consider a simple example where you need to create a drawable shape.

Use interface:

One way is to define an IDrawable interface:

interface IDrawable {
    public function draw();
}

Then create two classes to implement this Interface:

class Circle implements IDrawable {
    public function draw() {
        // 绘制圆形的具体实现
    }
}

class Square implements IDrawable {
    public function draw() {
        // 绘制正方形的具体实现
    }
}

Use abstract class:

Another way is to define an abstract class Shape:

abstract class Shape {
    public function draw() {
        // 共享的绘制实现
    }

    abstract public function getArea();
}

Then Create two classes that inherit from the abstract class:

class Circle extends Shape {
    public function getArea() {
        // 计算圆面积的具体实现
    }
}

class Square extends Shape {
    public function getArea() {
        // 计算正方形面积的具体实现
    }
}

Which approach is more appropriate depends on the specific requirements. If only a drawing contract is needed, an interface is appropriate. If you need to share implementation and concrete methods, abstract classes are a better choice.

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