PHP notes for Java programmer (4) - classes
Here is the last set of PHP notes which cover object oriented programming in PHP. The notes conclude with a set of supplementary notes. The entire list of PHP notes are available here.
PHP Notes - Object oriented programming
1. To call class methods without an instance, use scope resolution operator(::) else use (->). Check the following example,
class test {
function f1() {
echo “hello”;
}
}
test::f1();
$t1 = new test();
$t1->f1();
2. In PHP, __autoload function (automatically called) can be used to simulate “import” functionality. This is very handy if you store your classes in separate PHP files. For example,
<?php
function __autoload($class_name) {
require_once $class_name . ‘.php’;
}
$obj = new MyClass1();
$obj2 = new MyClass2();
?>
3. PHP has constructors (__construct()) and destructors (__destruct()). There is no chaining of constructor or destructor calls. Use parent::__construct() for the same.
4. Method and properties can have “public”, “private” or “protected” visibility.
5. Use const keyword to define constants inside classes.
6. PHP has the standard class constructs - abstract, extends, interface, implements etc.
7. It is possible to overload method calls and member access using __call, __get and __set. This will be triggered only if the accessed attribute or method doesn’t exist! isset() and unset() can also be overridden using __isset() and __unset().
8. For serialization methods __sleep and __wakeup. All methods starting with __ are reserved as magic methods in PHP!
9. To perform shallow copy, use clone directive. It is also possible to define a __clone() method.
10. PHP supports reflection paradigm. For more details, checkout http://www.php.net/manual/en/language.oop5.reflection.php
11. PHP supports type hinting for object and array types. For example, function f1(array $a) { }
12. A typical PHP class declaration is shown below,
class Test extends T1 implements T2 {
public $a;
public function testmethod($value) {
$this->a = $value;
}
}
13. PHP exception handling is similar to Java. It is also possible to extend the base “Exception” class. Here is a sample use of exception,
try {
$error = ‘error message’;
throw new Exception($error);
} catch (Exception $e) {
echo ‘Caught exception: ‘, $e->getMessage(), “\n”;
}
PHP supplementary notes
1. For maximum security always validate user input. You don’t want to be a victim of SQL injection attack!
2. For database access, provide least access rights needed by the application.
3. On a production system it is better to disable error reporting.
