1. More on Classes & Arrays
Pepper
With help from

2. Review - A Class Trace Exercise
What's wrong with the following program?
public class SomethingIsWrong { public static void main(String[] args) { Rectangle myRect; myRect.width = 40; myRect.height = 50; System.out.println ("myRect's area is " + myRect.area()); } }

3. Class Extension
Make sub-classes (put "extends " classname after class)
Can use the entire extended class
Can override methods
This is how we use Fang's game class
Can see all protected and public methods and variables

4. Class Extension - Super
Can choose to execute methods from the super class using super.methodname

5. Player Extension Make one player Extend to different player types
Example:

6. Abstraction
If you know you will make a lower class, you don't have to implement all methods
You can mark a class as abstract (public abstract class) and then put only the method headers. Compiler complains if the lower class does not implement it.

7. Interface Can create a type that has only abstract methods.
Basically a contract to implement interfaces
Contains method headers with no code below it.
Lower classes can implement many interfaces (but only extend one class)
Implementing an interface means you promise (and the compiler checks) that you will implement the methods listed.

8. More on Arrays – For Each
Shortcut for loop through an array:
for (variable to hold value : array name)
Ex:
int[] arr= {1,2,3,4}; int tot = 0; for (int x : arr) { tot = tot + x;} System.out.println(tot);

9. ArrayList An Array class Has methods you can use
Can make an array of anything using <type>
ArrayList<String> myArr = new ArrayList<String>();
ArrayList<Player> guys = new ArrayList<Player>();

10. ArrayList Methods Methods
add( Object o ) - puts reference to object into ArrayList
get( int index ) - retrieves object reference from ArrayList index position
size() - returns ArrayList size
remove( int index ) - removes the element at the specified position in this list. Shifts any subsequent elements to the left and returns the element that was removed from the list.
indexOf( Object o) - finds the index in this list of the first occurrence of the specified element
clear() - removes all of the elements

11. ArrayList of Players
guys.add(new Player("Amy")); guys.add(new Player("Jim"));
guys.