What does “implements” do on a class?

Question

If a class implements another class... what does that mean? I found this code sample: http://www.java2s.com/Code/Php/Class/extendsandimplement.htm

But unfortunately

Answer 1

Interfaces are implemented through classes. They are purely abstract classes, if you will.

In PHP when a class implements from an interface, the methods defined in that interface are to be strictly followed. When a class inherits from a parent class, method parameters may be altered. That is not the case for interfaces:

interface ImplementMeStrictly {
   public function foo($a, $b);
}

class Obedient implements ImplementMeStrictly {
   public function foo($a, $b, $c) 
      {
      }
}

will cause an error, because the interface wasn't implemented as defined. Whereas:

class InheritMeLoosely {
   public function foo($a)
      {
      }
}

class IDoWhateverWithFoo extends InheritMeLoosely {
   public function foo()
      {
      }
}

Is allowed.