Inner classes challenges

Author: bowbahdoe

src/SUMMARY.md

@@ -534,6 +534,7 @@ Have a project that is just klarna but the your goal is "never write this progra
   - [The anonymous main class](./inner_classes/the_anonymous_main_class.md)
   - [Static Inner Classes](./inner_classes/static_inner_classes.md)
   - [Private Inner Classes](./inner_classes/private_inner_classes.md)
+  - [Challenges](./inner_classes/challenges.md)
 - [Packages](./packages.md)
   - [Declaration](./packages/declaration.md)
   - [Visibility](./packages/visibility.md)

src/inner_classes/challenges.md

@@ -0,0 +1,108 @@
+# Challenges
+
+Remember the rules for this are
+
+- Try to use only the information given up to this point in this book.
+- Try not to give up until you've given it a solid attempt
+
+## Challenge 1.
+
+As written the code in `GameConsole.Controller`
+looks at its own `isPoweredOn` field. 
+
+Disambiguate the usage so that it is uses the `isPoweredOn` field from
+the `GameConsole` instance wrapping it in its `status` method.
+
+```java,editable
+class GameConsole {
+    boolean isPoweredOn;
+
+    GameConsole() {
+        this.isPoweredOn = false;
+    }
+
+    class Controller {
+        boolean isPoweredOn;
+
+        Controller() {
+            this.isPoweredOn = false;
+        }
+
+        String status() {
+            "Controller[" 
+                + isPoweredOn ? "ON" : "OFF" + "] - GameConsole["
+                + isPoweredOn ? "ON" : "OFF" + "]";
+        }
+    }
+}
+
+class Main {
+    void main() {
+        var console = new GameConsole();
+        var controller = console.new Controller();
+
+        IO.println(controller.status());
+
+        console.isPoweredOn = true;
+        IO.println(controller.status());
+
+        controller.isPoweredOn = true;
+        IO.println(controller.status());
+
+        console.isPoweredOn = false;
+        IO.println(controller.status());
+    }
+}
+```
+
+## Challenge 2.
+
+Make the `Controller` class from the previous example a `static` inner class.
+The `status` method should keep the same behavior. This means you will need
+to explicitly pass an instance of `GameConsole` to the constructor of `Controller`
+and store it in a field.
+
+## Challenge 3.
+
+Successfully make an instance of `Fly` from the `Main` class.
+
+```java,editable
+class OldLady {
+    class Horse {
+        class Cow {
+            class Goat {
+                class Dog {
+                    class Cat {
+                        class Bird {
+                            class Spider {
+                                class Fly {
+                                    Fly() {
+                                        IO.println("She's dead, of course");
+                                    }
+                                }
+                            }
+                        }
+                    }
+                }
+            }
+        }
+    }
+}
+
+class Main {
+    Fly f = /* CODE HERE */;
+    IO.println(f);
+}
+```
+
+## Challenge 4.
+
+Go back to some of the programs you wrote entirely within the anonymous
+main class. Turn that main class into a named class.
+
+First make sure your program works the same as it did. Then 
+go through all the inner classes in your program and mark them
+as many of them as you can `static`.
+
+Which ones can't be trivially made `static`? Note what state they
+access in the enclosing instance.