To demonstrate the use of a class, lets create one to model a bank account.A bank account has certain information associated with it, such as itsaccount number, the PIN number needed to access it, and its balance.
This information could be stored in a class’s member variables.Here is the class declaration with only the member variables declared:
These functions will be changing the value of certain member variableswithin the class. To do so, we must use the $this object. THE $this OBJECT$this is used to access the contents of an object from within its own memberfunctions. To modify a variable from within a member function definition,you use $this->variable_name, where variable_name is one of theclass’s member variables. For example, bank_account Class could be used to create a rudimentary checkbook-balancing program, as follows:
class bank_account
{
var $Number, // (string) Account Number (xxx-xxxx-xxxx)
$PIN, // (int) PIN Number (xxxx)
$Balance; // (double) Balance (xxxx.xx)}
Like all other variables in PHP, object variables are not persistent; that is, each time PHP runs, the object that exists has to be re-created. It is not the same object everytime the user clicks a Deposit or Withdraw button. This is why the previous-balance hidden field is included in the form.
<?php
// MAIN PROGRAM
$in = $HTTP_POST_VARS;
switch($in[‘action’])
{
default:
showForm();
break;
case ‘Deposit’:
$objAccount = new bank_account;
$objAccount->Balance = $in[‘previous-balance’];
$objAccount->Deposit($in[‘amount’]);
showForm($objAccount->Balance);
break;
case ‘Withdraw’:
$objAccount = new bank_account;
$objAccount->Balance = $in[‘previous-balance’];
$objAccount->Withdraw($in[‘amount’]);
showForm($objAccount->Balance);
break;
}
// FUNCTION DEFINITIONS
function showForm($dblBalance = 0)
// PRE: none
// PST: An HTML form is displayed to allow input into the program
{
?><html><head><title>Pela PHP Tutorial</title></head>
<body bgcolor=”white”>
<form action=”<?= $GLOBALS[‘PHP_SELF’] ?>” method=”POST”>
<!-- hidden input to track balance from one submission to the next -->
<input type=”hidden” name=”previous-balance” value=”<?= $dblBalance ?>”>
<b>Account Balancing Program</b><br>
Previous Balance: <?= $dblBalance ?><br>
Amount: <input type=”text” name=”amount”><br>
<input type=”submit” name=”action” value=”Withdraw”><br>
<input type=”submit” name=”action” value=”Deposit”>
</form>
</body>
</html>
<?php
}
// end of showForm()
// CLASS DEFINITIONS
class bank_account
{
var $Number, // (string) Account Number (xxx-xxxx-xxxx)
$PIN, // (int) PIN Number (xxxx)$
Balance; // (double) Balance (xxxx.xx)
function Deposit($dblAmount)
{
$this->Balance += $dblAmount;
}
function Withdraw($dblAmount)
{
$this->Balance -= $dblAmount;
}
}
?>
As you can see, the first time the program runs (when the user first visitsit), no action is defined. In response, the program simply returns the form.
Rating: 22
