


Static Methods and Properties
We can not only access methods and properties through objects, but also through classes. Such methods and properties are "static" (static) and must be declared with the static keyword.
class StaticExample{ static public $aNum=0; static public function sayHello() { self::$aNum++; print "hello (".self::$aNum.")/n"; } } print StaticExample::$aNum;StaticExample::sayHello();
Static methods are functions with class as scope. Static methods cannot access normal properties in this class because those properties belong to an object, but static properties can be accessed. If you modify a static property, all instances of the class can access the new value. When accessing static elements, use :: to connect class names and attributes or class names and methods. To access a static method or property from the current class, you can use the self keyword. self points to the current class, just like the pseudo variable $this points to the current object. By definition, we cannot call static methods in objects, so static methods and properties are also called class variables and properties, so pseudo variables cannot be used in static methods.
The following constructs a static method of the ShopProduct class to automatically instantiate the ShopProduct object. Use sqlite to define the table products as follows:
CREATE TABLE products( id INTEGER PRIMARY KEY AUTOINCREMENT, type TEXT, firstname TEXT, mainname TEXT, title TEXT, price float, numpages int, playlength int, discount int )
The getInstance() method is constructed below, and its parameters are the id of the database record and the pdo object. Use them to get a row of records from the database, and then return the ShopProduct object.
//ShopProduct类, private $id = 0; //... public function setID($id) { $this->$id; } //... public static function getInstance($id, PDO $pdo) { $stmt = $pdo->prepare("select * from products where id=?"); $result = $stmt->execute(array($id)); $row = $stmt->fetch(); if (empty($row)) { return null; } if ($row['type'] == "book") { $product = new BookProduct( $row['title'], $row['firstname'], $row['mainname'], $row['price'], $row['numpages'] ); } else if ($row['type'] == "cd") { $product = new CdProduct( $row['title'], $row['firstname'], $row['mainname'], $row['price'], $row['playlength'] ); } else { $product = new ShopProduct( $row['title'], $row['firstname'], $row['mainname'], $row['price'] ); } $product->setID($row['id']); $producerMainName->setDiscount($row['discount']); return $product; } //...
As long as there is a valid PDO object, we can call this method anywhere in the program:
$dsn = "sqlite://home/bob/projects/products.db";$pdo = new PDO($dsn, null, null); $pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION); $obj = ShopProduct::getInstance(1, $pdo);
Such a method is like a "factory" and can accept raw data (such as A column of data or configuration information), and then generate objects based on this.
PHP5 can define constant attributes in the class. Constant attributes are declared with the const keyword. Constants do not start with a dollar sign like regular properties. By convention, constants can only be named with uppercase letters. Constant attributes can only contain basic data types , and constant attributes can only be accessed through classes.
class ShopProduct{ const AVAILABLE = 0; const OUT_OF_STOCK = 1; //...}print ShopProduct::AVAILABLE;
The above is the detailed content of In-depth understanding of PHP object-oriented, patterns and practices-advanced features (1). For more information, please follow other related articles on the PHP Chinese website!

php把负数转为正整数的方法:1、使用abs()函数将负数转为正数,使用intval()函数对正数取整,转为正整数,语法“intval(abs($number))”;2、利用“~”位运算符将负数取反加一,语法“~$number + 1”。

实现方法:1、使用“sleep(延迟秒数)”语句,可延迟执行函数若干秒;2、使用“time_nanosleep(延迟秒数,延迟纳秒数)”语句,可延迟执行函数若干秒和纳秒;3、使用“time_sleep_until(time()+7)”语句。

php字符串有下标。在PHP中,下标不仅可以应用于数组和对象,还可应用于字符串,利用字符串的下标和中括号“[]”可以访问指定索引位置的字符,并对该字符进行读写,语法“字符串名[下标值]”;字符串的下标值(索引值)只能是整数类型,起始值为0。

php除以100保留两位小数的方法:1、利用“/”运算符进行除法运算,语法“数值 / 100”;2、使用“number_format(除法结果, 2)”或“sprintf("%.2f",除法结果)”语句进行四舍五入的处理值,并保留两位小数。

在php中,可以使用substr()函数来读取字符串后几个字符,只需要将该函数的第二个参数设置为负值,第三个参数省略即可;语法为“substr(字符串,-n)”,表示读取从字符串结尾处向前数第n个字符开始,直到字符串结尾的全部字符。

判断方法:1、使用“strtotime("年-月-日")”语句将给定的年月日转换为时间戳格式;2、用“date("z",时间戳)+1”语句计算指定时间戳是一年的第几天。date()返回的天数是从0开始计算的,因此真实天数需要在此基础上加1。

方法:1、用“str_replace(" ","其他字符",$str)”语句,可将nbsp符替换为其他字符;2、用“preg_replace("/(\s|\ \;||\xc2\xa0)/","其他字符",$str)”语句。

查找方法:1、用strpos(),语法“strpos("字符串值","查找子串")+1”;2、用stripos(),语法“strpos("字符串值","查找子串")+1”。因为字符串是从0开始计数的,因此两个函数获取的位置需要进行加1处理。


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