PHP，OOP，静态

Question

I am studying PHP,OOP and i am at Static, At this php.net/static i didnt understand this sentence

Calling non-static methods statically generates an E_STRICT level warning.

I did understand it's Valid for methods only (not for Properties) by the sentence above, but i didn't succeed to understand It practically, I'm glad if anything could please show me code that explains the sentence above, Wishing you a pleasant week.

Answer 1

Here is an example of what they mean with the sentence you are asking about.

Consider the following class with one method (it is not static).

class Test
{
    function method()
    {
        echo "Hello from method";
    }
}

Test::method();  // attempt to statically call a non-static method

This is the output:

Strict Standards : Non-static method Test::method() should not be called statically in /obj.php on line 12
Hello from method

As you can see, it did execute the method when called static even though it is not a static method, however a strict error message was displayed.

If the method method() referenced the keyword $this , then you would encounter a fatal error because $this does not exist in the context of a static method call. So while it is technically possible to call a non-static class method statically, it should not be done.

EDIT:

The reason you are even allowed to call a non-static class member statically is because the static keyword did not exist in PHP4 in the context of class methods so if you were designing a static class or method in PHP4, there was no keyword to indicate it, you would simply call it in the static fashion. Now PHP5 emits the warning if the method is called statically but doesn't have the static keyword in the declaration.

Answer 2

class Foo
{
    public static $my_static = 'foo';
    public $my_non_static = 'bar';

    public function staticValue() {
        return self::$my_static;
    }

    public function nonStaticValue() {
        return self::$my_non_static;
    }
}

print Foo::$my_static . "\n"; // OK
print Foo::staticValue(). "\n"; // E_STRICT

print Foo::$my_non_static . "\n"; // Fatal
print Foo::nonStaticValue(). "\n"; // Fatal

print Foo::$my_static . "\\n"; is OK - static property accessed statically.

print Foo::staticValue(). "\\n"; gives E_STRICT - non-static method accessed statically, but not Fatal error, because this method doesn't access non-static properties.

Other two give Fatal error because non-static field cannot be accessed statically.

Answer 3

It's because even if you can call non-static methods statically, you shouldn't and it will be logged.

class Foo {
    function bar(){
        print "you should not do that";
    }
} 

Foo::bar(); would actually works, but you will get a E_STRICT warning because you can do that, but you shouln't .

Answer 4

If a method is non-static, it means that it belongs to an instance of a class. For example, if we have a class Car with a method called getDamage() (which computes how much damaged the car is), then you should not call this method in a static way.

You should only create an instance of the Car class and call getDamage() on that instance. This makes sense because a particular car can be damaged for 25% while another car can be damaged for 70%.

But calling getDamage() in a static way makes no sense: a static method does not belong to a particular instance of the class but to the class itself. And a Car class has no useful way of giving a result for getDamage() . You could still compute a value (perhaps 0 ) but it does not make sense.