Wordpress oop wpdb in class

I am new in OOP PHP and I am trying to use $wpdb (WORDPRESS) object in some of my custom classes but have no idea how to do it. Every time I try to implement basic operations with $wpdb results in fail.
I need some basic stuff like get_results(),....
So how to do something like this:

global $wpdb;

$my_custom_table = $wpdb->prefix . "table_name";

$table_content = $wpdb->get_results("SELECT * FROM ".$my_custom_table);

and put it into my class like this:

Class MyClass{

public function table_results(){
//put in here
return $this->table_content;
}
}

I need that class in separate file so I could easily call to it.

Try this...

<?php
class MyClass {

private $wpdb;

public function __construct()
{
global $wpdb;
$this->wpdb = $wpdb;
}

public function table_results(){
$my_custom_table = $this->wpdb->prefix . "table_name";

$table_content = $this->wpdb->get_results("SELECT * FROM $my_custom_table");
return $table_content;
}
}