<?php

interface CatI
{
    public function walk();
    public function feed();
}

abstract class Cat implements CatI
{
    protected $paws = 4;

}

class Tiger extends Cat
{
    public $power = 100;

    public function __construct()
    {
        echo $this->paws;
    }

    public function walk() {}
    public function feed() {}
}

$myCat = new Tiger(); // 4