How to use abstract classes in php?

Abstract class is a special class that cannot be instantiated but can only be inherited. In PHP, an abstract class can be defined by using the keyword abstract and it can contain abstract methods and implementation methods. This article will introduce the detailed use of abstract classes in PHP.

1. Define abstract class

To define an abstract class, you need to use the keyword abstract. Abstract classes can contain abstract methods and implementation methods.

The following is the definition of a basic abstract class:

<?php
    abstract class Shape {
        abstract public function getArea();
    }
?>

In this example we define an abstract class Shape, which contains an abstract method getArea(). This method has no specific implementation and subclasses need to override it.

2. Inherit abstract class

Subclasses can inherit abstract classes and implement its abstract methods and implementation methods.

The following is an example of inheriting the Shape abstract class:

<?php
    class Circle extends Shape {
        private $radius;
        public function __construct($radius) {
            $this->radius = $radius;
        }
        public function getArea() {
            return pi() * pow($this->radius, 2);
        }
    }
?>

In this example, we define a Circle class that inherits the Shape abstract class. It implements the abstract method getArea(), which calculates the area of ​​a circle.

3. Using abstract classes

You need to pay attention to the following points when using abstract classes:

1. Abstract classes cannot be instantiated.
2. If a class inherits an abstract class, it must implement abstract methods.

The following is a complete example:

<?php
    abstract class Shape {
        abstract public function getArea();
    }
    class Circle extends Shape {
        private $radius;
        public function __construct($radius) {
            $this->radius = $radius;
        }
        public function getArea() {
            return pi() * pow($this->radius, 2);
        }
    }
    $circle = new Circle(10);
    echo "圆的面积是：" . $circle->getArea();
?>

In this example, we use the abstract class Shape and the subclass Circle. The abstract method getArea() is implemented in the subclass Circle to calculate the area of ​​the circle. Finally, calculate the area of ​​the circle by instantiating the Circle class.

4. Summary

Abstract class is a tool that can help you design better code. By defining abstract methods in an abstract class, you establish a set of conventions so that other developers can better understand your code.

At the same time, abstract classes also allow you to implement polymorphism in your application. Subclasses can inherit abstract classes and implement abstract methods as needed to achieve polymorphism.

Please remember the following points when using abstract classes:

1. Abstract classes cannot be instantiated;
2. Subclasses must implement abstract methods;
3. Abstract classes can contain implementation methods.

I hope everyone can master the use of abstract classes in the process of learning PHP.

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