traits與interfaces有什麼差別？

<?php
trait MyTrait
{
    protected $var = &#39;MyTrait_var&#39;;
    protected $var1 = &#39;MyTrait_var&#39;;
 
    function __construct()
    {
        echo $this->var."</br>";
    }
 
    function a()
    {
        echo "a"."</br>";
    }
}
 
interface MyInterface
{
    function __construct();
    function b();
}
 
abstract class MyAbstract
{
    protected $var2 = &#39;MyAbstract_var&#39;;
    use MyTrait;
 
    function b()
    {
        echo "b"."</br>";
    }
}
 
class MyClass extends MyAbstract implements MyInterface
{
    protected $var3 = &#39;MyClass_var&#39;;
    function c()
    {
        echo "c"."</br>";
    }
}
 
$class = new MyClass();
$class->a();
$class->b();
$class->c();