PHP permission control modifier analysis: in-depth analysis of the characteristics and functions of various modifiers

In web application development, permission control is a very important function, especially when the application involves user authentication and the protection of sensitive information. In PHP, permission control modifiers are a common tool used to control access permissions to classes, properties, and methods. This article will deeply analyze the characteristics and functions of various permission control modifiers in PHP, and demonstrate their use through specific code examples.

1. public modifier

public is the most basic modifier in PHP, which means that classes, properties and methods can be accessed. In other words, if a class, property or method is declared public, they can be accessed from anywhere. For example:

class Car {
    public $color; // public属性
    public function drive() { // public方法
        echo "Driving";
    }
}

The above code defines a class named Car, which contains a public property $color and a public method drive(). Since these members are public, they can be accessed and called by any other code, for example:

$myCar = new Car();
$myCar->color = "red"; // 访问public属性
$myCar->drive(); // 调用public方法

2. protected modifier

protected is another one in PHP Permission modifier, which indicates that the class and its subclasses can access the property or method, but other code cannot. For example:

class Car {
    protected $color; // protected属性
    protected function drive() { // protected方法
        echo "Driving";
    }
}

In the above code, both $color and drive() are declared protected, so only the Car class and Code in their subclasses can access and call them. For example:

class SportsCar extends Car {
    public function set_color($color) {
        $this->color = $color; // 可以访问protected属性
    }
}

$sportsCar = new SportsCar();
$sportsCar -> set_color("blue"); // 调用public方法

The above code defines a subclass named SportsCar, and defines a public method in it, through which the Car class can be set The protected attribute $color. Since SportsCar inherits the Car class, it can access and call the protected members in the Car class.

3. private modifier

private is the most restrictive permission modifier in PHP, used to indicate that only code in the class can access the member. No other classes or objects can access or call it. For example:

class Car {
    private $mileage; // private属性
    private function update_mileage() { // private方法
        $this -> mileage++;
    }
}

In the above code, both $mileage and update_mileage() are declared as private, only in the Car class Only code can access and call them. For example:

$myCar = new Car();
$myCar->mileage = 1000; // 这里会报错，因为$mileage是私有的
$myCar->update_mileage(); // 这里会报错，因为$update_mileage()是私有的

The above code demonstrates that private properties cannot be accessed and modified outside the class and private methods cannot be called.

4. final modifier

In addition to the above three permission modifiers, there is another modifier in PHP: final. final can be used in classes, properties and methods to indicate that they are "final", that is, they cannot be inherited or overridden by subclasses. For example:

class Car {
    final public function drive() { // final public方法
        echo "Driving";
    }
}

class SportsCar extends Car {
    public function drive() { // 这里会报错，因为drive()被声明为final
        echo "Driving fast";
    }
}

The above code defines a class named Car, which contains a final public method drive(). In the SportsCar class, try to override the drive() method, but because it is declared final in the Car class, the code generates an error. This means that the method has been defined as final and cannot be modified by subclasses.

Summary

In this article, we have deeply analyzed the characteristics and functions of various permission modifiers in PHP. Public allows access and calls from anywhere, protected allows access and calls to the class and its subclasses, and private only allows access and calls within the class. Final means that these members are in a "final state" and cannot be modified by subclasses. Understanding how to use these permission modifiers is key to good permission control and code design.

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