Difference: Once defined, const cannot be changed, while variables modified by static can be changed. const can only modify class attributes, not class methods; static can modify attributes as well as methods.
The operating environment of this tutorial: windows7 system, PHP7.1 version, DELL G3 computer
static and The difference between const variables
static variables
1.static static variables we can modify them , but we cannot modify const variables
2.static static variables can modify permissions
3.Similar to java, inside the class, satic The body of the modified method cannot access non-staic member variables of the class, but can only access the class's staic variables and the class's const constants
class staticTest1 { var $var1 = "hello"; public static $var2 = "hellostatic"; //public, protected, private const var3 = "helloconst"; public static function displayDifferent(){ ### echo $this->$var1."<br>";//不能访问普通变量 echo staticTest1::$var2."<br>";//可以访问类的静态变量 echo self::var3."<br>";//不能用$this::var3, self::var3代表当前类,$this::var3代表当前对象 } }
//You can call the method in two ways
//第一种,通过对象调用 $test1 = new staticTest1(); echo $test1->displayDifferent(); echo "<br>"; //第二种,通过类调用 echo staticTest1::displayDifferent(); echo "<br>";
By the way, "::" can only access static variables and methods for objects, and self can only use "::" to call members of the current class
const variables
1. Const variables can only modify member variables, not methods
2. No modification permission is required
3 .Because const variables belong to the entire class and do not belong to an object, they cannot be accessed through objects. For example, $this->constvariable does not allow
class constTest1 { var $var1 = "welcome"; // public const pi = 3.14;//不能加修饰权限 const pi = 3.14; // const function displayDifferent() {//function前不能加const // // } function displayDifferent() { echo self::pi."<br>"; // echo $this::pi."<br>"; } static function displayDifferent2() { echo self::pi."<br>"; // echo $this::pi."<br>"; //这句话不行。 } }
two method calls
//第一种,通过对象调用 $test2 = new constTest1(); echo $test2->displayDifferent(); //第二种,通过类调用 //echo constTest1::displayDifferent();//对象名用"::"只能访问静态变量和方法,所以这个不行 echo constTest1::displayDifferent2();
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php把负数转为正整数的方法:1、使用abs()函数将负数转为正数,使用intval()函数对正数取整,转为正整数,语法“intval(abs($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。

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。

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。


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