For interfaces and traits :
<?php
interface TestInterface { }
trait TestTrait { }
$interfaceClass = new ReflectionClass('TestInterface');
$traitClass = new ReflectionClass('TestTrait');
var_dump($interfaceClass->isAbstract());
var_dump($traitClass->isAbstract());
?>
Using PHP versions 5.4- to 5.6, the above example will output:
bool(false)
bool(true)
Using PHP versions 7.0+, the above example will output:
bool(false)
bool(false)