Understand how to use static variables in php

The concept of static needs to be used when dealing with classes. There are contents called members (properties) in the class. If it is not defined with the static modifier If it is shipped, it will be managed by examples. Therefore, this article will introduce to you how to use static variables in PHP.

For example, we define a person class and define the name attribute in the person class

Then we instantiate and create a For an instance named "Zhang San", there will be a person named Zhang San at this time.

Then we instantiate and create an instance named "李思" from the person class, so that there will be a person named Li Si.

We can see that each instance manages a name. In this case, name is a property named instance variable or local variable.

Corresponding to instance variables are called static variables or class variables. This is an item jointly managed between classes; because we don’t know how it is different from instances, we will proceed further in the person class below. illustrate.

We define a new family attribute in the person class. Family is different from name. Therefore, the person whose name is Aoki and the person whose name is Yamada, no matter which one is family.

When using a class after defining it, use the New operator to create an instance.

Let’s look at how to write static variables

// person类的定义
class Person{

  // 成员
  public $name;           // 名为name的实例变量
  public static $family;  //  family的static变量/类变量

Let’s look at a specific example

Let’s instantiate it The person class that appeared before

// 定义person类
class Person {

  // 成员
  public $name;                     // 名为name的实例变量
  public static $family = ""ヒト科""; // family的static变量/类变量

}

// 名为张三的人
$aoki = new Person();
$aoki->name = ""张三"";

// 名为李四的人
$yamada = new Person();
$yamada->name = ""李四"";

// static变量可以直接从类中调用！
echo Person::$family.PHP_EOL;   

// 让我们检查一下每个实例！
echo $zhangsan->name.PHP_EOL;       // 张三
echo $zhangsan::$family.PHP_EOL;    
echo $lisi->name.PHP_EOL;     // 李四
echo $lisi::$family.PHP_EOL;  

// 更改了static变量，因为与类的所有实例共享，所以结果都改变了！
Person::$family = ""哺乳动物"";
echo Person::$family.PHP_EOL;    // 哺乳动物
echo $zhangsan::$family.PHP_EOL;    // 哺乳动物
echo $lisi::$family.PHP_EOL;  // 哺乳动物

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