Abstract Class vs. Interface [duplicate]

Question

I have searched around SO as well as the rest of the web for a good answer but I have't found one that I really understand. I am going to present this in a different way and hopefully the answers will help others as well.

As far as I understand, the two concepts have the same rules except an abstract class is more flexible due to the method implementation ability. Also, I am aware you can implement multiple interfaces and only extend a single class but I'm sure there are more differences than the two I mentioned.

Please look at the two snippets of code and give me an example what I can do with each of my examples that would make me want or not want to use the other.

Abstract Class

abstract class Foo {     abstract public function getValue();     abstract public function setValue($value);  }   class myObj extends Foo {     function getValue() {      }     function setValue($value) {      } } 

Interface

interface Foo {     public function getValue();     public function setValue($value); }  class myObj implements Foo {     function getValue() {      }     function setValue($value) {      } } 

Answer 1

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();