PHP class and constructor analysis

Everyone has a certain understanding of classes. Here we only introduce the noteworthy aspects of classes in php

----Creation of classes----

php uses the keyword class Create a class and use a pair of braces
such as:

class name{
  public $n="";
  private $u="";

  public function name() {
    $n="233";
    $u="23333";
  }

  public function rename($newn){
     $this->n=$newn;//this表示这个类
  }
}

without a semicolon at the end. Then $n, $u are fields; name() is a constructor (__construct() can also define a constructor, see below for details), which can assign values ​​to fields; rename() is a method.

----Field----

Compare
$obj=new name();
echo $obj->n;
with
$obj=new name();
echo $obj->u;

The former is executable, but the latter is not possible because private is declared before $u. This is similar to c++.

Code:

public static $nm ="2333333333333333" ;

Declares a static field for the function.
The variable can be accessed directly through the class name and ::

echo name::$nm;

This is also similar to c++.

In php, you can also access static fields in the class through self::+$+variable name. At this time, self is equivalent to $this->.

Methods are used similarly to fields

----Constructor----

Constructed in php5 and earlier versions The function has the same name as the class

In PHP5 and later versions, the magic word __construct() can define the constructor

The magic word __construct() can define the constructor

class name{
  public $n="";
  private $u="";

  public function __construct() {
    $n="233";
    $u="23333";
  }

  public function rename($newn){
     $this->n=$newn;
  }
}

The constructor can have parameters

__construct($name="",$sex="man",$age=0){}

When declaring an object

$obj= new name("I","man",28);

If no parameters are given, the default is the value after = .

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