Question

the code here outputs 20, 20, why the private property can be accessed here:

class myClass {
    private $a;

    public function __construct() {
      $this->a = 10;
    }

    public function printValue() {
       print "The Value is: {$this->a}\n";
    }

    public function changeValue($val, $obj = null) {
        if(is_null($obj)) {
            $this->a = $val;
        } else {
           $obj->a = $val; //why this works?
        }
     }

    public function getValue() {
      return $this->a;
     }
 }

 $obj_one = new myClass();
 $obj_two = new myClass();

 $obj_one->changeValue(20, $obj_two);
 $obj_two->changeValue($obj_two->getValue(), $obj_one);

 $obj_two->printValue();
 $obj_one->printValue();

any ideas?

Answer 1

For the purpose of encapsulation, it’s important that the internals of a class be protected from access by other parts of code that must not know about the internals of the class. The class itself presumably knows about its internals and can access private properties of instances of itself just fine.