Page 221 - Beginning PHP 5.3

Chapter 8: Objects

public function getTotalBalance() {
return $this- > _totalBalance;
}
}

$a = new Account;
$a- > makeDeposit( 500 );
$a- > makeWithdrawal( 100 );
echo $a- > getTotalBalance() . “ < br / > ”; // Displays “400”;

$a- > makeWithdrawal( 1000 ); // Displays “Insufficient funds”
Because the variable storing the account balance is private, it can ’ t be manipulated directly. Customers
have to actually make a deposit via makeDeposit() if they want to increase the value of their account.
By encapsulating internal data and method implementations, an object - oriented application can protect
and control access to its data and hide the details of implementation, making the application more
flexible and more stable.

Object Overloading with get(),
—
set(), and call()
— —
Normally, if you try to read or write an object ’ s property, PHP dutifully reads or sets the property ’ s value
(assuming the property exists and your code has permission to access it). Similarly, if you call an object ’ s
method, PHP looks for the method within the object and, if it finds it, runs it.
However, PHP lets you use a technique known as overloading to intercept attempts to read or write an
object ’ s properties, or call its methods. This can be quite powerful. As far as the calling code is
concerned, the object contains fixed, pre - programmed properties and methods. However, behind the
scenes, your object can be doing all sorts of interesting things. For example:
❑ The calling code reads the value of $myObject - > property , which actually causes $myObject

to retrieve the value from an array instead
❑ The calling code sets $myObject - > anotherProperty to a new value, but behind the scenes

$myObject actually writes this value to a database field
❑ The calling code calls $myObject - > aMethod() . This method doesn ’ t actually exist in

$myObject , but $myObject intercepts the call and calls another method instead
Although you probably won ’ t use object overloading that often, you can see that the technique can offer
you a lot of flexibility.

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