http://www.php.net/manual/en/migration5.oop.php

In PHP 5 there is a new Object Model. PHP's handling of objects has been completely rewritten, allowing for better performance and more features. In previous versions of PHP, objects were handled like primitive types (for instance integers and strings). The drawback of this method was that semantically the whole object was copied when a variable was assigned, or passed as a parameter to a method. In the new approach, objects are referenced by handle, and not by value (one can think of a handle as an object's identifier).

在PHP 5中通过引用传递对象，在PHP 4中通过值传递对象。 默认情况下，变量是按值传递的!

阅读此处:http://www.webeks.net/programming/php/ampersand-operator-used-for-assigning-reference.html

取决于版本，4是值，5是引用。

http://www.php.net/manual/en/migration5.oop.php

In PHP 5 there is a new Object Model. PHP's handling of objects has been completely rewritten, allowing for better performance and more features. In previous versions of PHP, objects were handled like primitive types (for instance integers and strings). The drawback of this method was that semantically the whole object was copied when a variable was assigned, or passed as a parameter to a method. In the new approach, objects are referenced by handle, and not by value (one can think of a handle as an object's identifier).

在PHP中，默认情况下，对象作为新对象的引用传递。

请看这个例子:

class X {
  var $abc = 10; 
}

class Y {

  var $abc = 20; 
  function changeValue($obj)
  {
   $obj->abc = 30;
  }
}

$x = new X();
$y = new Y();

echo $x->abc; //outputs 10
$y->changeValue($x);
echo $x->abc; //outputs 30

现在看这个:

class X {
  var $abc = 10; 
}

class Y {

  var $abc = 20; 
  function changeValue($obj)
  {
    $obj = new Y();
  }
}

$x = new X();
$y = new Y();

echo $x->abc; //outputs 10
$y->changeValue($x);
echo $x->abc; //outputs 10 not 20 same as java does.

现在看这个:

class X {
  var $abc = 10; 
}

class Y {

  var $abc = 20; 
  function changeValue(&$obj)
  {
    $obj = new Y();
  }
}

$x = new X();
$y = new Y();

echo $x->abc; //outputs 10
$y->changeValue($x);
echo $x->abc; //outputs 20 not possible in java.

我希望你能理解。

PHP变量按值赋值，按值传递给函数，当包含/表示对象时通过引用传递。可以使用“&”强制变量通过引用传递。

由值/引用示例赋值:

$var1 = "test";
$var2 = $var1;
$var2 = "new test";
$var3 = &$var2;
$var3 = "final test";

print ("var1: $var1, var2: $var2, var3: $var3);

输出:

Var1:测试，var2:最终测试，var3:最终测试

按值/引用示例传递:

$var1 = "foo";
$var2 = "bar";

changeThem($var1, $var2);

print "var1: $var1, var2: $var2";

function changeThem($var1, &$var2){
    $var1 = "FOO";
    $var2 = "BAR";
}

输出:

foo, var2 BAR

引用示例传递的对象变量:

class Foo{
    public $var1;

    function __construct(){
        $this->var1 = "foo";
    }

    public function printFoo(){
        print $this->var1;
    }
}


$foo = new Foo();

changeFoo($foo);

$foo->printFoo();

function changeFoo($foo){
    $foo->var1 = "FOO";
}

输出:

喷火

(最后一个例子可能更好。)