What are the best practices for defining and utilizing variables within a PHP class to prevent unexpected errors?

To prevent unexpected errors when defining and utilizing variables within a PHP class, it is best practice to declare class properties with appropriate visibility (public, protected, private) and initialize them with default values if necessary. Additionally, use getter and setter methods to access and modify class properties, enforcing data encapsulation and preventing direct manipulation of variables from outside the class.

class MyClass {
    private $myProperty;

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

    public function getMyProperty() {
        return $this->myProperty;
    }

    public function setMyProperty($newValue) {
        $this->myProperty = $newValue;
    }
}

// Implementation
$obj = new MyClass('default');
echo $obj->getMyProperty(); // Output: default
$obj->setMyProperty('new value');
echo $obj->getMyProperty(); // Output: new value