Abstract class and interface

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abstract class A{
    abstract function operationX($param1,$param2);
}
interface B
{
    function display();
}
class C extends A implements B 
{
    private $val;
    function __construct($v){
	$this->val=$v;
    }
    function operationX($param1,$param2){
	$this->val = $param1*$param2;
    }
    function display() { echo $this->val."
"; }
}

$foo = new C(34);
$foo->display();
$foo->operationX(10,3);
$foo->display();

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