I found this case
** php example **
abstract class class1{
function test(){}
}
abstract class class2 extends class1{
abstract function test();
}
This oop concept works in Java, in PHP it doesn't.(Cannot make non abstract method class1::test() abstract in class class2)
What other subtle differences there are between Java and PHP oop ?
Java and PHP (even when using OO PHP) have a vast array of differences.
Just a few thoughts off the top of my head:
Java is strongly-typed, PHP is not, although there is a limited scope for type-hinting in PHP. This makes a huge difference to method signatures. In PHP, you can only force method parameters to be of a certain class or interface or an array:
public function myMethod(SomeClass $foo, array $bar){}
...but you cannot type-hint for primitives! So public function myMethod(int $foo, boolean $bar){} is invalid and will throw a parse error.
Furthermore, any parameter that has been type-hinted cannot be passed as null unless null is given as a default value. So to allow nulls, you need to use:
public function myMethod(SomeClass $foo = null)
PHP does not require (or even support) specifying the return type of a function.
PHP classes do not have final fields, although what would be a static final field in Java is a const in PHP. EDIT: A const in PHP is more limited than a static final in Java as the latter can be an array or object instance, whereas the former must be a constant value (number or a string, essentially).
"Overloading" in PHP does not mean the same as it does in Java. In Java, it means specifying multiple methods of the same name, but with a different set of parameters:
public void myMethod(int foo){}; public void myMethod(float foo){};
In PHP, it refers to the dynamic creation of properties and methods using the __get(), __set() and __callStatic() "magic" methods. See the PHP manual for a description on their use. Java-style method overloading is impossible in PHP and an attempt to redeclare a method (with or without a different set of parameters) will fail.
May be obvious to some, but in PHP you use :: to access static methods and properties and -> to access instance ones, but in Java . is used for both.
PHP doesn't have packages, but it does have namespaces.
As of PHP5, constructors in PHP are not supposed to be methods with a name that matches the class, like in Java, but the magic method __construct() should be declared instead, although the PHP4 style is supported for backward-compatibility. Also, PHP has a destructor method named __destruct().
In Java, all classes inherit from Object, but there is no such generic super-class in PHP.
Even when maximizing the amount of OOP in a PHP script, it still relies on a procedural flow; there's no class-level entry point like in Java (i.e., public static void main(String[] args) or public void init() for applets).