如何将所有php类包含在一个文件中？

All the questions here refer to how import files into a directory, I'm looking for a smart way that allows me to import all the classes in a single class. Specifically, suppose that I have a structure like this:

\ Root 'Main folder

  Bootstrap.php 'This is the main class

     \System
          Core.php
          Language.php
          Helper.php

Now in Bootstrap.php for import the Core, Language, Helper classes I should do something like this:

include "System/Core.php";
include "System/Languages.php";
include "System/Helper.php;"

private $_core;
private $_languages;
private $_helper;

public function __construct()
{
    $this->_core      = new Core();
    $this->_languages = new Languages();
    $this->_helper    = new Helper();
}

Suppose that the files are more than 20, it would be a pain to import everything. So what would be a smart way to import all the classes and access their functions?

I am not really sure why you would like to do that but it can easily be done:

foreach(glob('System/*.php') as $file) include_once "System/$file";

May be you should have a look at autoloading: http://php.net/manual/en/language.oop5.autoload.php

// Register autoloader
spl_autoload_register(function ($class_name) {
  $fullPath = 'System/' . $class_name . '.php';
  if(file_exists($fullPath)) include $fullPath;
});

// Simply create a new object, class will be included by autoloader
$helper = New Helper();

This is a really simple autoloader but I hope you get the idea of it.