PHP의 인터페이스와 추상 클래스, 인터페이스와 추상 클래스의 차이점

<?php 
# 接口
interface Human{ 
    const TEST_CONST = "test const"; // 定义常量
    // public $v; // error，不能定义变量 
    // static $count; // error，不能定义变量 
    public function speak(); 
    public function walk(); 
    public function run(); 
} 
# 抽象类
abstract class Father implements Human{
    public function construct(){ 
        echo "father init n"; 
    }
    abstract public function walk(); // 抽象方法
    public function speak(){ 
        echo "father speak skill n";
    }
    public function run(){
        echo "father run skill n"; 
    }
} 
# 非抽象类
class Mother implements Human{
    public function construct(){
        echo "mother init n";
    }
    # 这里必须实现walk方法 
    public function walk(){ 
        echo "mother walk skill n"; 
    }
    public function speak(){
         echo "mother speak skill n"; 
    }
    public function run(){ 
        echo "mother run skill n"; 
    } 
}
class Son extends Father{ 
    public function walk(){
         echo "son walk skill. n"; 
    }
    public function speak($name = &#39;&#39;){
         echo "son: ". $name ." speak skill. n"; 
    }
    # 访问控制必须和父类中一样（或者更为宽松） 
    protected function sport(){ 
        echo "son sport skill. n"; 
    }
    final public function notTeach(){ 
        echo &#39;son has not to teach skill&#39;; 
    } 
}
 
class Daughter extends Mother{
    public function run($name = &#39;&#39;){ 
        echo "daughter run skill. n"; 
    }
}
final class GrandChild extends Son{
    # 访问控制必须和父类中一样（或者更为宽松） 
    public function sport(){ 
        echo "GrandChild sport skill. n"; 
    }
    # Cannot override final method Son::notTeach() 
    // public function notTeach(){} // error 
}
 
#  Class Orphan may not inherit from final class (GrandChild) 
// class Orphan extends GrandChild{}  // error
$son = new Son(); 
$son->speak("Suly"); 
$daughter = new Daughter(); 
$daughter->run(&#39;Lily&#39;);
$grandChild = new GrandChild();
$grandChild->sport();