Just posting some example code for anyone wanting to mess around with this stuff:

<?php

class Say
{
    private $what_to_say;
    public function __construct($no_default, $word = "Hello World", $options = array('a', 'b'))
    {
        $this->what_to_say = $word;
    }
    
    public function speak()
    {
        echo $this->what_to_say;
    }
}

$class = new ReflectionClass('Say');

$constructor = $class->getConstructor();

echo $constructor;

/*     OUTPUTS:

Method [ <user, ctor> public method __construct ] {
  @@ /reflect.php 6 - 9

  - Parameters [3] {
    Parameter #0 [ <required> $no_default ]
    Parameter #1 [ <optional> $word = 'Hello World' ]
    Parameter #2 [ <optional> $options = Array ]
  }
}

*/

$parameters = $constructor->getParameters();

var_export($parameters);

/*    OUTPUT:

array (
  0 => 
  ReflectionParameter::__set_state(array(
     'name' => 'no_default',
  )),
  1 => 
  ReflectionParameter::__set_state(array(
     'name' => 'word',
  )),
  2 => 
  ReflectionParameter::__set_state(array(
     'name' => 'options',
  )),
)

*/

$nl = "\n";
echo "$nl\tParameters$nl";
foreach($parameters as $param)
{
    echo "****** $" . $param->name . " ******$nl";
    echo "Nullable:\t\t" . $param->allowsNull() . $nl
         ."Default Value:\t\t";
    echo ($param->isDefaultValueAvailable()) ? $param->getDefaultValue() : "None";
    echo $nl ."Is Array:\t\t";
    echo ($param->isArray()) ? "Yes" : "No";
    echo $nl . "Optional:\t\t";
    echo ($param->isOptional()) ? "Yes" : "No";
    echo $nl;
}

/*    OUTPUT:

    Parameters
****** $no_default ******
Nullable:        1
Default Value:    None
Is Array:        No
Optional:        No
****** $word ******
Nullable:        1
Default Value:    Hello World
Is Array:        No
Optional:        Yes
****** $options ******
Nullable:        1
Default Value:    Array
Is Array:        No
Optional:        Yes

*/

?>

To clarify the possibly confusing behavior of ReflectionParemeter::isArray(), it will return true if the parameter has type hinting:

<?php
...
public function __construct($no_default, $word = "Hello World", array $options = array('a', 'b'))
...
?>

Calling isArray() will now return true for the $options parameter