Abstract Class vs. Interface [duplicate]

Abstract

Abstract Classes focus on a kind of things similarity.

People are considered of type mammal and as such would not be considered of type vehicle.

Interface

Interfaces focus on collation of similar function.

For example: You are a human being and are of type mammal. If you want to fly then you will need to implement a flying Interface. If you want to shoot while flying, then you also need to implement the gun Interface.

See the examples below:

abstract class Mammal {
      protected $age_;
      //below are functions I think all mammals will have,including people
      abstract public function setAge($age);
      abstract public function getAge();
      abstract public function eat($food);
}
class Person extends Mammal {
      protected $job_; //Person's feature
      public function setAge($age){
        $this->age_ = $age;
      }

      public function getAge(){
        return $this->age_;
      }

      public function eat($food){
        echo 'I eat ' ,$food ,'today';
      }

      //People only attribute
      public function setJob($job){
         $this->job_ = $job;
      }
      public function getJob(){
         echo 'My job is ' , $this->job_;
      }

}

//Now a person wants to fly, but they are typically not able to do so.
//So we implement an interface
interface Plane{
  public function Fly(); 
}

//I also want shoot enemy
interface Gun{
  public function shoot();
}

class Person2 extends Mammal implements Plane,Gun{

      protected $job_;//Person feature
      public function setAge($age){
        $this->age_ = $age;
      }
      public function getAge(){
        return $this->age_;
      }
      public function eat($food){
        echo '<br/>I eat ' ,$food ,' today<br/>';
      }
      //Only a person has this feature.
      public function setJob($job){
         $this->job_ = $job;
      }
      public function getJob(){
         echo 'My job is ' , $this->job_;
      }

      //-----------------------------------------
      //below implementations from interfaces function. (features that humans do not have).
      //Person implements from other class
      public function fly(){
        echo '<br/>I use plane,so I can fly<br/>';
      }
      public function shoot(){
        echo 'I use gun,so I can shoot<br/>';
      }
}

$People = new Person();
echo '<pre>';
print_r( get_class_methods('People'));
echo '</pre>';

echo '<pre>';
print_r( get_class_methods('People2'));
echo '</pre>';

$People2 = new Person2();
$People2->setAge(24);
echo $People2->getAge();
$People2->eat('egg');
$People2->setJob('PHP devepop');
echo $People2->getJob();

$People2->fly();
$People2->shoot();