Design principles of encapsulation in PHP

The design principle of encapsulation in PHP requires specific code examples

Encapsulation is one of the important principles of object-oriented programming. It is mainly used to hide the internals of objects. Implementation details only expose necessary interfaces for external access. Encapsulated design can improve code reusability, maintainability and security. In PHP, we can use classes and access modifiers to achieve encapsulated design.

1. Encapsulating data members
   In PHP, we can use three access modifiers: private, protected, and public to control attribute access permissions. Private properties can only be accessed within the class, protected properties can be accessed within the class and subclasses, and public properties can be accessed from anywhere. By setting data members as private or protected, we can avoid direct external access to the object's properties, thus hiding the object's internal implementation details.

Code example:

class User {
    private $name;
    protected $age;
    public $email;

    public function __construct($name, $age, $email) {
        $this->name = $name;
        $this->age = $age;
        $this->email = $email;
    }

    public function getName() {
        return $this->name;
    }

    public function getAge() {
        return $this->age;
    }

    public function getEmail() {
        return $this->email;
    }

    public function setName($name) {
        $this->name = $name;
    }

    public function setAge($age) {
        $this->age = $age;
    }

    public function setEmail($email) {
        $this->email = $email;
    }
}

$user = new User("John", 25, "john@example.com");

echo $user->getName(); // 输出：John
echo $user->getAge(); // 输出：25
echo $user->getEmail(); // 输出：john@example.com

$user->setName("Tom");
$user->setAge(30);
$user->setEmail("tom@example.com");

echo $user->getName(); // 输出：Tom
echo $user->getAge(); // 输出：30
echo $user->getEmail(); // 输出：tom@example.com

In the above example, we set the $name attribute to private, the $age attribute to protected, and the $email attribute to public of. By providing corresponding getter and setter methods for each property, external code can access and modify the object's properties through these methods without directly accessing the properties themselves.

2. Encapsulation method
   In addition to encapsulating data members, we can also encapsulate the behavior of the object, that is, encapsulation methods. By setting methods as private or protected, we can control external code's access to an object's behavior, thus hiding the object's internal implementation details.

Code example:

class Calculator {
    private function add($a, $b) {
        return $a + $b;
    }

    protected function subtract($a, $b) {
        return $a - $b;
    }

    public function multiply($a, $b) {
        return $a * $b;
    }

    public function divide($a, $b) {
        if ($b != 0) {
            return $a / $b;
        } else {
            return "除数不能为0！";
        }
    }
}

$calculator = new Calculator();

echo $calculator->multiply(2, 3); // 输出：6
echo $calculator->divide(10, 5); // 输出：2
echo $calculator->add(2, 3); // 报错：无法访问私有方法

In the above example, we set the add method as private, the subtract method as protected, and the multiply and divide methods as public of. External code can call the object's behavior through the multiply and divide methods, but it cannot call private methods directly.

Summary:
Encapsulation is one of the important principles of object-oriented programming. In PHP, encapsulation design can be achieved through classes and access modifiers. By encapsulating data members and encapsulating methods, we can hide the internal implementation details of the object and improve the reusability, maintainability and security of the code.

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