Static variables in PHP

Question

I have found different information regarding static variables in PHP but nothing that actually explains what it is and how it really works.

I have read that when us

Answer 1

class Student {
static $total_student = 0;
static  function add_student(){
    return Student::$total_student++;
}
}

First: for the add_student function, the best practice is to use static not public. Second: in the add_student function, we are using Student::$total_student,not use $this->total_student. This is big different from normal variable. Third:static variable are shared throughout the inheritance tree.

take below code to see what is the result:

class One {
static $foo ;
}
class Two extends One{}
class Three extends One{}
One::$foo = 1;
Two::$foo = 2;
Three::$foo = 3;
echo One::$foo;
echo Two::$foo;
echo Three::$foo;`