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8 years ago
An interface specifies what methods a class must implement, so that anything using that class that expects it to adhere to that interface will work.

eg: I expect any $database to have ->doQuery(), so any class I assign to the database interface should implement the databaseInterface interface which forces implementation of a doQuery method.

<?php
interface dbInterface {
    public function doQuery();
}

class myDB implements dbInterface {
    public function doQuery() {
      /* implementation details here */
    }
}

$myDBObj = new myDB()->doQuery();
?>

An abstract class is similar except that some methods can be predefined. Ones listed as abstract will have to be defined as if the abstract class were an interface.

eg. I expect my $person to be able to ->doWalk(), most people walk fine with two feet, but some people have to hop along :(

<?php
interface PersonInterface() {
    /* every person should walk, or attempt to */
    public function doWalk($place);
    /* every person should be able to age */
    public function doAge();
}

abstract class AveragePerson implements PersonInterface() {
    private $_age = 0;
    public function doAge() {
        $this->_age = $this->_age+1;
    }
    public function doWalk($place) {
        echo "I am going to walk to $place".PHP_EOL;
    }
    /* every person talks differently! */
    abstract function talk($say);
}

class Joe extends AveragePerson {
    public function talk($say) {
       echo "In an Austrailian accent, Joe says: $say".PHP_EOL;
    }
}

class Bob extends AveragePerson {
    public function talk($say) {
        echo "In a Canadian accent, Bob says: $say".PHP_EOL;
    }
    public function doWalk($place) {
        echo "Bob only has one leg and has to hop to $place".PHP_EOL;
    }
}

$people[] = new Bob();
$people[] = new Joe();

foreach ($people as $person) {
    $person->doWalk('over there');
    $person->talk('PHP rules');
}
?>
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