A class has only one object instance
1. Meaning
As an object creation mode, the singleton mode ensures that a certain class has only one instance. And instantiate it yourself and provide this instance globally to the entire system. It does not create a copy of the instance, but returns a reference to the instance stored inside the singleton class.
Related learning recommendations: PHP programming from entry to proficiency
2. Three key points of singleton mode:
(1). A static member variable is needed to save the only instance of the class:
private static $_instance;
(2). The constructor and clone function must be declared private to prevent external programs from creating new classes and thus losing the meaning of the singleton mode. :
private function __construct(){ $this->_db = pg_connect('xxxx'); } private function __clone(){ }//覆盖__clone()方法,禁止克隆
(3). You must provide a public static method to access this instance (usually the getInstance method), thereby returning a reference to the only instance
public static function getInstance(){ if(! (self::$_instance instanceof self) ){ self::$_instance = new self(); } return self::$_instance;
Single case mode Ensure that a class has only one instance, instantiates itself and provides this instance to the entire system.
The singleton mode is a common design pattern. In computer systems, thread pools, caches, log objects, dialog boxes, printers, database operations, and graphics card drivers are often designed as singletons.
There are three types of singleton modes: lazy-style singleton, hungry-style singleton, and registration-style singleton.
The singleton mode has the following three characteristics:
1. There can only be one instance.
2. You must create this instance yourself.
3. This instance must be provided to other objects.
So why use PHP singleton mode?
One of the main application scenarios of PHP is the scenario where the application deals with the database. In an application, there will be a large number of database operations. For the behavior of connecting the database handle to the database, using the singleton mode can avoid a large number of operations. new operation. Because every new operation consumes system and memory resources.
class Single { private $name;//声明一个私有的实例变量 private function __construct(){//声明私有构造方法为了防止外部代码使用new来创建对象。 } static public $instance;//声明一个静态变量(保存在类中唯一的一个实例) static public function getinstance(){//声明一个getinstance()静态方法,用于检测是否有实例对象 if(!self::$instance) self::$instance = new self(); return self::$instance; } public function setname($n){ $this->name = $n; } public function getname(){ return $this->name; } } $oa = Single::getinstance(); $ob = Single::getinstance(); $oa->setname('hello world'); $ob->setname('good morning'); echo $oa->getname();//good morning echo $ob->getname();//good morning
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php把负数转为正整数的方法:1、使用abs()函数将负数转为正数,使用intval()函数对正数取整,转为正整数,语法“intval(abs($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。

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。

php判断有没有小数点的方法:1、使用“strpos(数字字符串,'.')”语法,如果返回小数点在字符串中第一次出现的位置,则有小数点;2、使用“strrpos(数字字符串,'.')”语句,如果返回小数点在字符串中最后一次出现的位置,则有。

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。

在PHP中,可以利用implode()函数的第一个参数来设置没有分隔符,该函数的第一个参数用于规定数组元素之间放置的内容,默认是空字符串,也可将第一个参数设置为空,语法为“implode(数组)”或者“implode("",数组)”。

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。


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