Code descriptions such as PHP classes and objects

Source: Internet
Author: User
Code descriptions for PHP classes and objects

1. Define and create classes and objects:

Define classes to use the class keyword. Example: Class Name {//attribute and method}

Create objects using the New keyword. For example: $p 1 = new class name, you can create multiple objects based on one class.

2. Class Property values

(1) In a class, in addition to declaring properties, you can assign a value to a property, but only specify a constant value for the property in the following ways:

Example 1:public $last _visitor = ' Donnan ';    Correct public $last _visitor = 9;    Correct public $last _visitor = Array (' Jesse ');    Correct public $last _visitor = Pick_visitor (); Error public $last _visitor = ' Chris '. '    9 ';        Error (2) The method in the class assigns a very measure to the variable: example 2:class guest_book{public $last _visitor; Public Function Update ($comment, $visitor) {if (!empty ($comments)) {Array_unshift ($this->comme                NTS, $comments);    $this->last_visitor = $visitor;    A method in a class assigns a very magnitude to a variable}}} (3) assigns a value to the variable in the process of creating the object, which is assigned in the constructor of the class.        A constructor refers to a method that is automatically called when a new object is created, with the name __construct () example 3:class guset_book{public $comments;        Public $last _visitor;            Public Function __consturct ($user) {$dbh = Mysqli_connect (' localhost ', ' username ', ' password ', ' site ');            $user = mysqli_real_escape_string ($DBH, $user);            $sql = "Select comments, last_visitor from guest_book where user = ' $user '";$r = Mysqli_query ($DBH, $sql);    if ($obj = Mysqli_fetch_object ($DBH, $r)) {$this->comments = $obj->comments;    Specify a value for the variable $this->last_visitor = $obj->last_visitor;    Specify a value for the variable}}} $GB = new Guest_book (' Stewart '); Specify a value for a variable
3. Inheritance and coverage
(1) by inheriting to extend an existing class, use the keyword extends:
Class class name extends parent class name {} (2) Overrides parent class method:    example 4:class db{    function GetResult () {        return $this->result;    }    function query ($sql) {        error_log ("Queryy () must Bue overridden by a database-specific child");        return false;    }} Class MySQL extends db{/////    MySQL class inherits the GetResult () method from the parent class DB, but re-implements its own specific MySQL method query ()    function query ($ SQL) {           $this->result = mysql_query ($sql);}    } (3) Precede the method name with the parent:: A method to explicitly invoke a parent class:    example 5:fuction Escape ($sql) {    $safe _sql = mysql_real_escape_string ($sql) ;     $safe _sql = Parent::escape ($safe _sql);    The parent method adds ' around $DQL;    return $safe _sql;} (4) Note: When a method in a subclass overrides a method in the parent class, the parent class's method is not automatically called unless explicitly referenced (parent::).
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