The advantage / disadvantage of private variables?

Question

I'm used to make pretty much all of my class variables private and create "wrapper" functions that get / set them:

class Something{
  private $var;

  function getVar(){
    $return $this->var;
  }

}

$smth = new Something();
echo $smth->getVar();

I see that a lot of people do this, so I ended up doing the same :)

Is there any advantage using them this way versus:

class Something{
  public $var;
}
$smth = new Something();
echp $smth->var;

?

I know that private means that you can't access them directly outside the class, but for me it doesn't seem very important if the variable is accessible from anywhere...

So is there any other hidden advantage that I missing with private variables?

Answer 1

It's called encapsulation and it's a very good thing. Encapsulation insulates your class from other classes mucking about with it's internals, they only get the access that you allow through your methods. It also protects them from changes that you may make to the class internals. Without encapsulation if you make a change to a variable's name or usage, that change propagates to all other classes that use the variable. If you force them to go through a method, there's at least a chance that you'll be able to handle the change in the method and protect the other classes from the change.