抽象類和接口在PHP中各有用途。1. 抽象類用于共享代碼、支持構(gòu)造函數(shù)和控制訪問(wèn)，包含抽象方法和具體方法。2. 接口用于定義行為契約，所有方法必須實(shí)現(xiàn)且默認(rèn)為公有，支持多重繼承。3. 自PHP 8起，接口可含默認(rèn)方法實(shí)現(xiàn)，但仍無(wú)構(gòu)造函數(shù)或狀態(tài)。4. 使用抽象類當(dāng)需封裝實(shí)現(xiàn)細(xì)節(jié)；用接口當(dāng)需定義跨類行為或構(gòu)建插件系統(tǒng)。5. 可結(jié)合使用：抽象類實(shí)現(xiàn)接口或?qū)⒍鄠€(gè)接口組合到一個(gè)抽象類中。選擇依據(jù)是是否需要結(jié)構(gòu)加共享行為（抽象類）還是僅結(jié)構(gòu)（接口）。

Abstract classes and interfaces in PHP both help enforce structure in object-oriented programming, but they serve different purposes and are used in different scenarios. Let’s break it down.

What Abstract Classes Can Do

An abstract class is a class that cannot be instantiated on its own and must be extended by other classes. It can contain both implemented methods and abstract methods (methods without a body).

• You can have method implementations – This means you can write actual code inside an abstract class.
• It supports constructors – So you can initialize values when a child class is created.
• You can define protected or private methods – Which gives you more control over visibility.

For example:

abstract class Animal {
    abstract public function makeSound();

    public function sleep() {
        echo "Zzz...";
    }
}

Here, makeSound() must be implemented by subclasses, but sleep() already has a body.

Use abstract classes when:

• You want to share code among closely related classes.
• You need to enforce a template but allow for some default behavior.
• You want to control access with protected/private methods.

What Interfaces Are For

An interface defines a contract — any class that implements the interface must provide the methods defined in it. But unlike abstract classes, interfaces can't have any implementation at all (prior to PHP 8.0; more on that later).

• Only method signatures – No implementation details allowed.
• Support multiple inheritance – A class can implement multiple interfaces.
• All methods must be public – No protected or private methods.

Example:

interface Logger {
    public function log($message);
}

A class using this would look like:

class FileLogger implements Logger {
    public function log($message) {
        // Write to file
    }
}

Interfaces are best when:

• You're defining behaviors that unrelated classes might need.
• You want to ensure certain methods exist across different parts of your app.
• You’re designing plugins or APIs where implementation details don’t matter, only method names do.

PHP 8 Changes: Default Methods in Interfaces

Starting from PHP 8, interfaces can now include method bodies. That means interfaces can offer default implementations, which blurs the line between interfaces and abstract classes a bit.

interface Renderer {
    public function render();

    public function getType() {
        return 'default';
    }
}

This makes interfaces more flexible, but there are still key differences:

• Interfaces still can't have constructors.
• They still can't have state (like properties), unless using traits or workarounds.
• You still can't restrict method visibility in interfaces.

So while interfaces gained some power, abstract classes are still better if you need internal logic and constructor support.

When to Use Each

In general:

Use abstract classes when:

• You have shared logic between similar objects.
• You need to encapsulate some implementation details.
• You want to define protected or private helper methods.

Use interfaces when:

• You want to define a behavior that many unrelated classes should follow.
• You're building something extensible, like a plugin system.
• You want to decouple your code from specific implementations.

Also, consider combining them:

• An abstract class can implement an interface.
• Or multiple interfaces can be grouped into one abstract class for convenience.

Basically, pick based on whether you need to enforce structure alone (interface) or structure plus some shared behavior (abstract class).

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