diff --git a/1.md b/1.md
index d9d46ba..e0aa964 100644
--- a/1.md
+++ b/1.md
@@ -109,7 +109,8 @@ $person->sayName(); //Joe Bob
 
 ##### Notes:
 
-Objects are always passed by reference (rather than making a copy of it), meaning that a function that accepts an object as a parameter can modify the original object passed to it.
+Objects are always passed by reference (rather than making a copy of it), meaning that a function 
+that accepts an object as a parameter can modify the original object passed to it.
 
 ## Coding Standards:
 
diff --git a/3.md b/3.md
index 2a4e905..de769c8 100644
--- a/3.md
+++ b/3.md
@@ -1,4 +1,4 @@
-# Lesson 3: Constructors
+# Lesson 3: Constructors and Type Hinting
 
 ## New Keywords:
  - `__construct`
@@ -81,7 +81,9 @@ class Person {
 
 ### Exercise:
 
- 1 Using the class from Exercise 2, create a constructor function that takes
+ 1 Using the class from Lesson 2, create a constructor function that takes
     a $name parameter and assigns that value to the name property.
 
- 2. Add 'height' and 'haircolor' to your constructor.
+ 2. Add 'height' and 'height' to your constructor.
+ 
+ 3. Make use of type hints in the arguments to the methods.
diff --git a/4.md b/4.md
index 1c5ec0c..f9d6389 100644
--- a/4.md
+++ b/4.md
@@ -90,3 +90,4 @@ $url = Url::fromUserInput('/robots.txt');
 ### Exercise:
 
  1. Add a static method to the "Person" class that compares two individuals by age and returns the oldest one.
+ 2. Call that static method.
diff --git a/5.md b/5.md
index 1d1b4f4..c212b05 100644
--- a/5.md
+++ b/5.md
@@ -51,7 +51,7 @@ class Node extends ContentEntityBase {
 
 ```
 
-###Protected: visibility
+### Protected: visibility
 
 Another level of visibility (information hiding) is "protected", which means that a protected property or method can be
 accessed only from within the class defining it, or any subclassses. In contrast, a private property/method is only
@@ -100,3 +100,10 @@ echo $b->private; // Fatal error
 $b->testVisibilityA(); // Public, Protected, Private
 $b->testVisibilityB(); // Fatal error: subclass can't access $this->private
 ```
+
+## Exercises:
+
+ - Add a method "sayHi()" to the Person class.
+ - Create two sub-classes "Developer" and "Designer" that extend the Person class.
+ - Add a method "work()" to each of those subclasses.
+ - Use "parent" in a sub-class method.
diff --git a/6.md b/6.md
index 9469dcf..fbf10af 100644
--- a/6.md
+++ b/6.md
@@ -126,9 +126,15 @@ class Select extends Query {
 }
 ```
 
+## `final`
+
+The `final` keyword prevents child classes from overriding a method by prefixing the definition 
+with final. If the class itself is being defined final then it cannot be extended. 
+
 ## Exercise:
 
- - Create an abstract class out of the Person class from lesson 2.
- - Create a concrete class that extends the abstract class.
- - Instantiate an object from the concrete class.
- - Set the name of the person object, and then echo it back out.
+ - Convert the Person class into an abstract class.
+ - Convert into concrete classes the Developer and Designer classes.
+ - Instantiate objects from the concrete classes.
+ - Call some methods on those objects to see how they behave.
+ - Try instantiating an object of the abstract class to look at the PHP error.
diff --git a/7.md b/7.md
index 9e2fe05..e9e1bee 100644
--- a/7.md
+++ b/7.md
@@ -99,7 +99,8 @@ and provide a consistent API for module developers.
 
 ## Exercise:
 
- - Create an interface to give a Person object from lesson 3 an email address and website.
- - Modify the concrete class from lesson 3 to implement your new interface.
- - Instantiate an object from the concrete class.
- - Set the email and website of the object, and then echo it back out.
+ - Create a person interface that declares the methods "work()" and "sayHi()".
+ - Modify the abstract class Person so it implements that interface.
+ - Instantiate an object from a concrete class.
+ - Review what errors does PHP give when a method declared in the interface is missing on the
+ implementing class.
diff --git a/9.md b/9.md
index 3c5344f..58b1439 100644
--- a/9.md
+++ b/9.md
@@ -36,7 +36,7 @@ namespace ChapterThree\OOTraining;
 
 class Person {
   public function __construct($filename) {
-    $array = \Symfony\Component\Yaml\Yaml::parse(file_get_contents($filename));
+    $array = \Symfony\Component\Yaml::parse(file_get_contents($filename));
     // ... Do something else.
   }
 }
@@ -49,7 +49,7 @@ Or by declaring the `use` keyword and adding the namespace to the top of the cla
 
 namespace ChapterThree\OOTraining;
 
-use Symfony\Component\Yaml\Yaml;
+use Symfony\Component\Yaml;
 
 class Person {
   public function __construct($filename) {
@@ -58,18 +58,20 @@ class Person {
   }
 }
 ```
-### Use as
+### Use `as`
+
+You can also create *aliases* to refer to the classes using `as`:
 
 ```php
 <?php
 
 namespace ChapterThree\OOTraining;
 
-use Symfony\Component\HttpKernel as kernel;
+use Symfony\Component\HttpKernel as Kernel;
 
 class Person {
   public function __construct($filename) {
-    kernel::terminate();
+    Kernel::terminate();
   }
 }
 ```
@@ -97,7 +99,6 @@ modules/chapterthree/
     chapterthree.module
 ```
 
-
 ## Exercise:
 
 - Add a namespace to the top of your file, this will put all classes defined in that file into that namespace.
diff --git a/code_samples/1.php b/code_samples/1.php
index 66e8323..d9698b4 100644
--- a/code_samples/1.php
+++ b/code_samples/1.php
@@ -1,15 +1,22 @@
 <?php
 
-function cat() {
-  $cat = new stdClass();
-  $cat->name = 'frank';
-  $cat->meow = function() {
-    echo 'meow';
-  };
-  return $cat;
+class Person {
+
+  public $name;
+  public $age;
+
+  function getName() {
+    return $this->name;
+  }
+
+  function getAge() {
+    return $this->age;
+  }
+
 }
 
-$cat1 = cat();
-unset($cat1->name);
-var_dump($cat1->name);
-call_user_func($cat1->meow);
+$person = new Person();
+$person->name = 'Arlina';
+$person->age = 32;
+
+var_dump($person);
diff --git a/code_samples/2.php b/code_samples/2.php
index f035288..f5ee5c2 100644
--- a/code_samples/2.php
+++ b/code_samples/2.php
@@ -1,13 +1,12 @@
 <?php
 
 class Person {
-  private $name;
 
-  function __construct($name) {
-    $this->name = $name;
-  }
+  private $name;
+  private $age;
+  private $height;
 
-  function setName($name) {
+  public function setName($name) {
     $this->name = $name;
   }
 
@@ -15,8 +14,27 @@ public function getName() {
     return $this->name;
   }
 
+  public function setAge($age) {
+    $this->age = $age;
+  }
+
+  public function getAge() {
+    return $this->age;
+  }
+
+  public function setHeight($height) {
+    $this->height = $height;
+  }
+
+  public function getHeight() {
+    return $this->height;
+  }
+
 }
 
-$person = new Person('asdf');
-$person->setName('ryryr');
-var_dump($person->getName());
+$person = new Person();
+$person->setName('Arlina');
+$person->setAge(32);
+$person->setHeight(160);
+
+var_dump($person);
diff --git a/code_samples/3.php b/code_samples/3.php
index 4960c67..6cc758d 100644
--- a/code_samples/3.php
+++ b/code_samples/3.php
@@ -1,13 +1,45 @@
 <?php
 
-function Person() {
-  $person = new stdClass();
-  $person->name = 'frank';
-  $person->talk = function() {
-    echo 'hi';
-  };
-  return $person;
+class Person {
+
+  private $name;
+  private $age;
+  private $height;
+  private $birth_year;
+
+  public function __construct(string $name = 'Anonymous', int $age = NULL, float $height = NULL) {
+    $this->name = $name;
+    $this->age = $age;
+    $this->height = $height;
+    $this->birth_year = date('Y') - $this->age;
+  }
+
+  public function setName(string $name) {
+    $this->name = $name;
+  }
+
+  public function getName() {
+    return $this->name;
+  }
+
+  public function setAge(int $age) {
+    $this->age = $age;
+  }
+
+  public function getAge() {
+    return $this->age;
+  }
+
+  public function setHeight(float $height) {
+    $this->height = $height;
+  }
+
+  public function getHeight() {
+    return $this->height;
+  }
+
 }
 
-$person = Person();
-var_dump(is_a($person, 'stdClass'));
+$person = new Person('Arlina', 32, 160);
+
+var_dump($person);
diff --git a/code_samples/4.php b/code_samples/4.php
new file mode 100644
index 0000000..13b0fcb
--- /dev/null
+++ b/code_samples/4.php
@@ -0,0 +1,53 @@
+<?php
+
+class Person {
+
+  private $name;
+  private $age;
+
+  public function __construct(string $name = 'Anonymous', int $age = NULL) {
+    $this->name = $name;
+    $this->age = $age;
+  }
+
+  public function setName(string $name) {
+    $this->name = $name;
+  }
+
+  public function getName() {
+    return $this->name;
+  }
+
+  public function setAge(int $age) {
+    $this->age = $age;
+  }
+
+  public function getAge() {
+    return $this->age;
+  }
+
+  /**
+   * Return the person who is older, or NULL if they have the same age.
+   *
+   * @param \Person $a
+   * @param \Person $b
+   *
+   * @return null|\Person
+   */
+  public static function returnWhoIsOlder(Person $a, Person $b) {
+    if ($a->getAge() > $b->getAge()) {
+      return $a;
+    }
+    elseif ($b->getAge() > $a->getAge()) {
+      return $b;
+    }
+
+    return NULL;
+  }
+
+}
+
+$personA = new Person('Arlina', 32);
+$personB = new Person('Methuselah', 969);
+$oldest = Person::returnWhoIsOlder($personA, $personB);
+echo $oldest->getName() . ' is older';
diff --git a/code_samples/5.php b/code_samples/5.php
index 4068d8d..815b384 100644
--- a/code_samples/5.php
+++ b/code_samples/5.php
@@ -1,30 +1,51 @@
 <?php
 
-abstract class APerson {
-  abstract function getName();
-  abstract function setName($name);
+class Person {
+  private $name;
+
+  public function getName() {
+    return $this->name;
+  }
+
+  public function setName(string $name) {
+    $this->name = $name;
+  }
 
   public function sayHi() {
-    echo "hi" . PHP_EOL;
+    echo "Hi";
   }
 }
 
-class CPerson extends APerson {
-  private $name;
+class Developer extends Person {
 
-  function getName() {
-    return $this->name;
+  public function work() {
+    echo 'Coding!' . PHP_EOL;
   }
 
-  function __construct() {
-    $this->sayHi();
+  public function sayHi() {
+    parent::sayHi();
+    echo "I'm a developer." . PHP_EOL;
   }
 
-  function setName($name) {
-    $this->name = $name;
+}
+
+class Designer extends Person {
+
+  public function work() {
+    echo 'Designing!' . PHP_EOL;
   }
+
+  public function sayHi() {
+    parent::sayHi();
+    echo "I'm a designer." . PHP_EOL;
+  }
+
 }
 
-$person = new CPerson();
-$person->setName('Alice');
-echo $person->getName();
+$programmer = new Developer();
+$programmer->sayHi(); // Hi I'm a developer.
+$programmer->work(); // Coding!
+
+$designer = new Designer();
+$designer->sayHi(); // Hi I'm a designer.
+$designer->work(); // Designing!
diff --git a/code_samples/6.php b/code_samples/6.php
new file mode 100644
index 0000000..f4b3a86
--- /dev/null
+++ b/code_samples/6.php
@@ -0,0 +1,53 @@
+<?php
+
+abstract class APerson {
+  private $name;
+
+  public function getName() {
+    return $this->name;
+  }
+
+  public function setName(string $name) {
+    $this->name = $name;
+  }
+
+  public function sayHi() {
+    echo "Hi";
+  }
+}
+
+class Developer extends APerson {
+
+  public function work() {
+    echo 'Coding!' . PHP_EOL;
+  }
+
+  public function sayHi() {
+    parent::sayHi();
+    echo "I'm a developer." . PHP_EOL;
+  }
+
+}
+
+class Designer extends APerson {
+
+  public function work() {
+    echo 'Designing!' . PHP_EOL;
+  }
+
+  public function sayHi() {
+    parent::sayHi();
+    echo "I'm a designer." . PHP_EOL;
+  }
+
+}
+
+//$person = new APerson(); // Error!
+
+$programmer = new Developer();
+$programmer->sayHi(); // Hi
+$programmer->work(); // Coding!
+
+$designer = new Designer();
+$designer->sayHi(); // Hi
+$designer->work(); // Designing!
diff --git a/code_samples/7.php b/code_samples/7.php
index 6dcafcf..c285a79 100644
--- a/code_samples/7.php
+++ b/code_samples/7.php
@@ -1,38 +1,64 @@
 <?php
 
 interface IPerson {
-  const NAME='Alice';
-  function getName();
+
+  public function getName();
+  public function setName(string $name);
+  public function sayHi();
+  public function work();
+
 }
 
-class BasicPerson implements IPerson {
-  private $name=IPerson::NAME;
+abstract class APerson implements IPerson {
+  private $name;
+
+  public function getName() {
+    return $this->name;
+  }
 
-  function getName() {
-    return $this->name . ' Basic';
+  public function setName(string $name) {
+    $this->name = $name;
   }
+
+  public function sayHi() {
+    echo "Hi";
+  }
+
+  abstract public function work();
 }
 
-class AdvPerson implements IPerson {
-  private $name=IPerson::NAME;
+class Developer extends APerson {
 
-  function getName() {
-    return $this->name . ' Advanced';
+  public function work() {
+    echo 'Coding!' . PHP_EOL;
   }
+
+  public function sayHi() {
+    parent::sayHi();
+    echo "I'm a developer." . PHP_EOL;
+  }
+
 }
 
-class Client {
-  function __construct() {
-    $basic = new BasicPerson();
-    $adv = new AdvPerson();
-    $this->sayHi($basic);
-    $this->sayHi($adv);
+class Designer extends APerson {
+
+  public function work() {
+    echo 'Designing!' . PHP_EOL;
   }
 
-  // Important type hinting, note that we're using the interface as the type.
-  function sayHi(IPerson $person) {
-    echo "Hi " . $person->getName() . PHP_EOL;
+  public function sayHi() {
+    parent::sayHi();
+    echo "I'm a designer." . PHP_EOL;
   }
+
 }
 
-$worker = new Client();
+//$person = new APerson(); // Error!
+
+$programmer = new Developer();
+$programmer->sayHi(); // Hi
+$programmer->work(); // Coding!
+
+$designer = new Designer();
+$designer->sayHi(); // Hi
+$designer->work(); // Designing!