Admin. CS 112 Introduction to Programming. Recap: Encapsulating Data. Ask, Don't Touch. Recap: Encapsulating Data. Recap: Encapsulation/How

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1 Adin CS Introduction to Prograing q Updated class schedule Design Good Classes: Encapsulation and OOP Analysis Yang (Richard) Yang Coputer Science Departent Yale University 308A Watson, Phone: Eail: yry@cs.yale.edu Recap: Encapsulating Data Recap: Encapsulating Data Client can see only the external API Client Methods q Benefit Consistency: so that it is ipossible for others to "reach in" and directly alter another object's state Client should not see the internal state or behaviors Data/state Flexibility: so that you can change the state representation later without worrying about breaking others code 3 Ask, Don't Touch q Encapsulated data types. Don't touch data and do whatever you want. Instead, ask object to anipulate its data. "Ask, don't touch." Recap: Encapsulation/How access odifiers enforce encapsulation public ebers (data and ethods: can be accessed fro anywhere Adele Goldberg Forer president of ACM Co-developed Salltalk private ebers: can be accessed fro a ethod defined in the sae class q Lesson. Liiting scope akes progras easier to aintain and understand. "principle of least privilege" Mebers without an access odifier: default private accessibility, i.e., accessible in the sae package; otherwise, not accessible. 6

2 Class Diagra Exaples: Set the Access Modifiers q Coin Coin class nae q Ball - face : int attributes q BankAccount + flip() : void + isheads() : boolean + tostring() : String ethods q Above is a class diagra representing the Coin class. - indicates private data or ethod + indicates public data or ethod 7 Outline 8 Data Visualization q Adin and recap q Defining classes o Motivation and basic syntax o Exaples o The encapsulation principle Ø An OOP exaple: geoap visualization If I can't picture it, I can't understand it. Albert Einstein Edward Tufte. Create charts with high data density that tell the truth. 9 Visualization based on Geography 0 A coposition Classes?

3 String A coposition Design question: - Iutable objects? 3 4 ing Controller Structure A coposition q Retrieve region Batch: retrieve list of all regions Specific: retrieve one specific region q ing Map properties of a region to a color Design question: - What is the basic controller (of ) structure? 5 6 A coposition A coposition - Public ethods (API) of - Public ethods (API) of 7 8 3

4 public class { private final int N; // nuber of boundary points private final [] points; // the points // read fro input strea public (Scanner input) { N = input.nextint(); points = new [N+]; for (int i = 0; i < N; i++) { points[i] = new ( input ); points[n] = points[0]; A coposition public void draw() { public void fill() { public boolean contains( p) { public centroid() { - Public ethods (API) of 0 Q: Should have a ethod that returns its internal? Exaple Controllers public class { private final String regionnae; // nae of region private final String apnae; private final poly; // polygonal boundary private fill, draw; public (String Nae, String rnae, poly) { regionnae = rnae; Even though ost coplexity apnae = Nae; is in, is not this.poly = poly; exposed. delegates setdefault(); tasks internally to. public void setdraw ( c) { draw = c; public void draw() { setdraw(); poly.draw (); public void fill() { public boolean contains( p) { return poly.contains(p); public centroid() { return poly.centroid() q.java q RandoMap.java q ClickMap.java q RedBlueMap.java Purple Aerica (PurpleMap.java) q Idea. [Robert J. Vanderbei] Assign color based on nuber of votes. a = Rep. votes. 00% Rep a = Other votes. a 3 = De. votes. 55% De, 45% Rep Cartogras q Cartogra. Area of state proportional to nuber of electoral votes. " a (R, G, B) = $, # a + a 3 a a + a 3, 00% Other a 3 % ' a + a 3 & 00% De public get() { int de = tally.de(), rep = tally.rep(), ind = tally.ind(); int tot = tally.de + tally.rep + tally.ind; return new ((float) rep/tot, (float) ind/tot, (float) de/tot); Michael Gastner, Cosa Shalizi, and Mark Newan www-personal.uich.edu/~ejn/election 4

5 Cartogras q Cartogra. Area of country proportional to population. Suary q Encapsulation is a key proble solving technique for large, coplex probles q A good way to learn ore is to read about designs of large-scale systes 5