1. Recitation 10
November 3, 2011

2. Today’s Goals:
Learn Generics
Practice with Generics

3. History Interface public interface History {
public void addElement(Object element);
public Object elementAt (int index);
public int size(); }

4. Generic History Interface
public interface History<T> {
public void addElement(T element);
public T elementAt (int index);
public int size(); }

5. AHistory public class AHistory<T> implements History<T> {
public final int MAX_SIZE = 50;
Object[] contents = new Object[MAX_SIZE];
int size = 0;
public int size() {return size;}
public T elementAt (int index) {
return (T) contents[index]; }
boolean isFull() {return size == MAX_SIZE;}
public void addElement(T element) {
if (isFull())
System.out.println("Adding item to a full history");
else {
contents[size] = element;
size++;
A single implementation where T = Object is shared by all of its elaborations.

6. Instantiating A String History
History<String> stringHistory = new AHistory<String>();
History<String> stringHistory = new AHistory();

7. Recitation Specification
Download Recitation10.zip from the Recitations page
Make changes to the given Stack interface to make it a “generic” interface. (Only change 3 lines)
Now implement the interface with a class named AStack which is a generic class. (default size >=200)
Internally just create an array of Objects to store the elements
Cast to the correct type before returning in the get method. (This will signal a warning, which is okay.)
Bonus (for candy): Create a “cool” design using the shape primitives provided, but specify coordinates using functions and loops. Ben will judge.