需要帮助理解php对象的各个方面

Question

i am new to php and is in need of some help to understand the aspects of php objects which i do not get. In class a i have made class b and c which extends a, but what i want to do is acess the public letters variable in class a from class c so in can get ot the function testb() from class c.

Any help is much appreciated guys

   <?php

    class a {
        public $letters;
        function __construct() {
            $this->letters->b = new b();
            $this->letters->c = new c();
        }
    }   

    class b extends a {
        function __construct() {
            echo "hello world from b ";
        }

        private function testb() {
            echo "testing from b";
        }
    }

    class c extends a {
        function __construct() {
            echo "hello world from c ";
            $this->letters->b->testb();
        }
    }


    $a = new a();

?>

the following script echos our "hello world from b" and "hello world from c" but it does not print out "testing from b"...

Answer 1

The reason you can't call testb from within the class c is that the method signature of testb declares it as private - meaning it can only be accessed within b instances. Change the visibility to default (no modifier) or public.

E.g.:

function testb() {
    echo "testing from b";
}

Or:

public function testb() {
    echo "testing from b";
}

Edit:

The problem is that you haven't called the super constructor from the constructor of c - the value of $this->b is therefore not initialised. Change the constructor of c to:

function __construct() {
    parent::__construct();
    echo "hello world from c ";
    $this->letters->b->testb();
}

Unfortunately, though, this will create an infinite loop where the constructor of a is instantiating c and the constructor of c is calling up to the constructor of a. Why do your letter classes even extend one another?

You also need to change the visibility of testb within the b class.