Class question - Beginner help

Question

Possible Duplicate:
In PHP, whats the difference between :: and -> ?

This a continuation from my previous question - however I think its unique enough to warrant a new question.

What is the difference between:

Message::listMessages();

and

$message->listMessages();

I'm creating a mini-cms and I want a system that displays errors in a uniform fashion.

Cheers, Keiran

score 1 · Answer 1 · answered Dec 08 '10 at 06:17

1

As i understood your question,

we are using this way Message::listMessages(); in C and C++

but right syntax we are using in PHP is $message->listMessages();

Thanks.

answered Dec 08 '10 at 06:17

Chandresh M

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2

PHP supports both the `::` and `->` operators but they mean different things. See the other answers for the explanation. – Asaph Dec 08 '10 at 06:25

score 1 · Answer 2 · answered Dec 08 '10 at 06:19

I assume your class Message is defined like this:

class Message {
  //...
  static function listMessages() {
    //...
  }
  //...
}

They are same, they both call the static method listMessages from Message, however, $message->listMessages() requires less lookup.

According to a test, you cannot declare two methods with same names, one static and one member:

$ php5-cgi 
<?php
class A { static function f() { }
          function f() { } }
?>
PHP Fatal error:  Cannot redeclare A::f() in - on line 2
Status: 500 Internal Server Error
X-Powered-By: PHP/5.3.2-1ubuntu4.5
Content-type: text/html

PHP allows you to define just one non-static method and call it statically or non-statically. Like this: `class A { function f() {} } A::f(); $a = new A(); $a->f();`. Not that I would recommend ever doing such nonsense, but PHP does allow it. — Asaph, Dec 08 '10 at 06:44

Asaph · Answer 3 · 2010-12-08T06:46:48.060

1

This is calling a static method, i.e. a method on a class:

Message::listMessages();

This is calling an instance method, i.e. a method on an object (aka instance of a class):

$message->listMessages();

edited Dec 08 '10 at 06:46

answered Dec 08 '10 at 06:19

Asaph

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Would the downvoter care to comment? – Asaph Dec 08 '10 at 06:46

score 1 · Answer 4 · answered Dec 08 '10 at 06:23

Message::listMessages() is a static function so it should be used when listMessages() is disregarding you're object propretyes , ie. return some class constants or variables or ... anything you like . ( static means it should have the same output for all instances of Message class )

$message->listMessages() may use you're object propretyes so output could be different for two different objects of the same Message class with different propretyes ( say $messages and $messages1 ) .

Stoic · Accepted Answer · 2010-12-08T06:39:13.293

Static methods come handy when we want to share information between objects of a class, or want to represent something that's related to the class itself, not any particular object.

The difference between the two is in the way they are invoked. For example, Message::listmessages() is a static method and can be called like this:

$messages = Message::listmessages($args);

You do not need to first make an object of class Message, in order to use the above. Also, note that this should be used when you want to return a result on definite pre-configured variables, and is not based on properties of class Message

However, $message->listmessages() is an instance method and can be called like this:

$message = new Message();
$messages->$args = $args
$messages= $message->listmessages();

This is used for generic occassions when you want to call a function on runtime properties of class Message.

score 0 · Answer 6 · answered Dec 08 '10 at 06:22

The class Message is calling its own method without an object means the method is static no object have rights to call this method only class can call.

Message::listMessages();

The object of class Message is calling the public method

$message->listMessages();

Class question - Beginner help

6 Answers6