The difference between self, parent and this in php class and an introduction to examples_PHP tutorial

class test{
public $public;
private $private;
protected $protected;
static $instance;
static $good = 'tankzhang
';
public $tank = 'zhangying
';

public function __construct(){
$this->public = 'public
';
$this->private = 'private
';
$this ->protected = 'protected
';

}
public function tank(){ //Private methods cannot be inherited, replace them with public, protected
if (!isset(self::$instance[get_class()]))
{
$c = get_class();
self::$instance = new $c;
}
return self::$instance;
}

public function pub_function() {
echo "you request public function
";
echo $this->public;
}
protected function pro_function(){
echo "you request protected function
";
echo $this->protected;
}
private function pri_function(){
echo "you request private function
";
echo $this->private;
}
static function sta_function(){
echo "you request static function
";
}
}

class test1 extends test{

static $love = "tank
";
private $aaaaaaa = "ying
";

public function __construct(){
parent::tank();
parent::__construct();
}
public function tank(){
echo $this-> ;public;
echo $this->protected;
echo $this->aaaaaaa;
$this->pro_function();
}

public function test1_function(){
echo self::$love;
echo self::$good;
echo parent::$good;
echo parent::$tank; / /Fatal error: Access to undeclared static property: test::$tank
echo self::$tank; //Fatal error: Access to undeclared static property: test::$tank
}
static function extends_function(){
parent::sta_function();
self::pro_function();
echo "you request extends_private function
";
}
}

error_reporting(E_ALL);
$test = new test1();
$test->tank(); //The subclass and the parent class have attributes and methods with the same name, instantiate the subclass , the method in the subclass will be called.
test1::test1_function();
test1::extends_function(); //After executing a part, a Fatal error is reported: Using $this when not in object context in D:xampphtdocsmytestwww4.php on line 32
?>