PHP 类的继承问题

/**
类和接口是不同的。类里是有程序实现的；而接口无程序实现，只可以预定义方法 extends 继承类
class A extends B implements C,D,E
extends 继承类implements 实现接口


abstract FilterIterator extends IteratorIterator implements OuterIterator {
// 方法 
public abstract bool accept ( void )//必须实现
public __construct ( Iterator $iterator )
public mixed current ( void )
public Iterator getInnerIterator ( void )
public mixed key ( void )
public void next ( void )
public void rewind ( void )
public bool valid ( void )
}

**/

class A{
    public $name = ‘A‘;
}
class B extends A{
    
}
class C extends B implements D,E{
    public function aa(){}//程序实现
    public function bb(){}

    public function dd(){}
}

interface D{
    //public $bb;报错
    //public function aa(){}//报错
    //private function bb();报错
    //protected function bb();报错
    public function aa();
    public function bb();
    
}
interface E{
    public function bb();
    public function dd();
    
}

$c = new C;
echo $c->name;


exit;