假设PHP 4,以及“一系列条形图”的想法

<?PHP
 
class foo {
  var $bars = array();
  function __construct() {
    "Foo Exists!";
  }
 
  function magic_bullet($id) {
    switch($id) {
    case 1:
      echo "There is no spoon! ";
    case 2:
      echo "Or is there... ";
      break;
    }
  }
 
  function addBar( &$bar )
  {
    $bar->setFoo( $this );
    $this->bars[] = &$bar;
  }
}
 
class bar {
  var $foo;
  function __construct() {
    echo "Bar exists";
  }
 
  function target($id){
    if ( isset( $this->foo ) )
    {
      echo $this->foo->magic_bullet( $id );
    } else {
      trigger_error( 'There is no foo!',E_USER_ERROR );
    }
  }
  function setFoo( &$foo )
  {
    $this->foo = &$foo;
  }
}
 
$test = new foo();
$bar1 = new bar();
$bar2 = new bar();
 
$test->addBar( $bar1 );
$test->addBar( $bar2 );
 
$bar1->target( 1 );
$bar1->target( 2 );