1. Data Structures 1 1

2. Computer is a machine that manipulates information
Dataypes
Computer is a machine that manipulates information
Need to organize, manipulate, and use information
This is done at different levels in the system
Bits (machine-level representation)
Built-in datatypes (language-level representation)
Arrays, objects (user-defined datatypes)

3. Convenient to separate specification from implementation
Data Structures
Convenient to separate specification from implementation
Abstract Data Types
Hide internal implementation of the data type
Allows correct use of the datatype from its specification
Allows composition of other useful data representations from the simpler ones (Data Structures)

4. Examples of Data Structures
Arrays
Drawback?
Lists
A collection of a variable number of items
Typical Operations of List ADT
Add an item to the list
Remove an item from the list
Read an item from the list
Check whether the list is empty
Get the current size of the list

5. Lists Can Be Organized in Different Ways
Linked List
Linear sequence of elements
Queue
Remove the item least recently added.
First-In, First-Out (FIFO)
Stack
Remove the item most recently added.
Last-In, First-Out (LIFO)

6. What About the Data Part?
Would like to be generic - support all data types
Java’s solution: The ArrayList Class

7. Generics (Dr. Java Code)
Generics. Parameterize stack by a single type.
You need to import the library: import java.util.ArrayList;
parameterized type
parameterized type
ArrayList<Apple> list= new ArrayList<Apple>();
Apple a = new Apple();
Orange b = new Orange();
list.add(a);
list.add(b); // compile-time error
a = list.get(0); // returns an Apple object
1) Change String to ints in the sample code.
sample client 7 7

8. Autoboxing
Generic ArrayList implementation. Only permits reference types.
Wrapper type.
Each primitive type has a wrapper reference type.
Ex: Integer is wrapper type for int.
Autoboxing. Automatic cast from primitive type to wrapper type.
Autounboxing. Automatic cast from wrapper type to primitive type.
syntactic sugar: casts are still done behind the scenes (hidden cost)
ArrayList<Integer> list= new ArrayList<Integer>();
list.add(17); // autobox (int -> Integer)
int a = list.get(i); // autounbox (Integer -> int) 8 8

9. Queues

10. Queue Applications Some applications. iTunes playlist.
Data buffers (iPod, TiVo).
Asynchronous data transfer (file IO, pipes, sockets).
Dispensing requests on a shared resource (printer, processor).
Simulations of the real world.
Traffic analysis.
Waiting times of customers at call center.
Determining number of cashiers to have at a supermarket.
CD players – use buffer to make skip-free ("shock protection")
Lincoln tunnel: can you make a left turn off of 10th avenue onto 31st? Just changed and now 90 minute delays. Someone didn't simulate the consequences (properly).
Graph processing (stay tuned for breadth first search). 10 10

11. Queue API Iterator<Key> iterator()
return an iterator over the keys
enqueue
dequeue
length
public static void main(String[] args) {
Queue<String> q = new Queue<String>();
q.enqueue(”No Country For Old Men");
q.enqueue(”Dark Knight");
q.enqueue(”Pulp Fiction");
q.enqueue(”Dude, Where Is My Car?");
while(!q.isEmpty())
StdOut.println(q.dequeue()); }
Hypothetical Netflix queue

12. Array Implementation of Queues
With an array q[].
Head (Keep track of the front of the queue)
Tail (Keep track of the back of the queue)
How do we enqueue elements?
How do we remove elements?
head
tail

13. Arraylist Implementation (Coding Demo)

14. Queue: “Circular” Array Implementation
Array implementation of a queue.
Use array q[] to store items on queue.
enqueue(): add new object at q[tail].
dequeue(): remove object from q[head].
Update head and tail modulo the capacity.
the
best of
times
q[] 1 2 3 4 5 6 7 8 9
head
tail
capacity = 10