PHP Interface Declaration: Syntax & Implementation

In PHP, the keyword ‘interface’ can be used to declare an interface. An interface is an abstract class that defines a set of methods without implementing them.

Here is an example demonstrating how to declare an interface in PHP.

<?php

// 声明一个接口
interface Shape {
    public function calculateArea();
}

// 实现接口的类
class Circle implements Shape {
    private $radius;

    public function __construct($radius) {
        $this->radius = $radius;
    }

    public function calculateArea() {
        return M_PI * pow($this->radius, 2);
    }
}

// 使用接口
$circle = new Circle(5);
echo 'Circle Area: ' . $circle->calculateArea();

In the example above, we declare an interface called Shape, which includes a method called calculateArea. We then create a class called Circle, and implement the calculateArea method from the Shape interface. Finally, we create a Circle object and call the calculateArea method to calculate the area of the circle.