1 / 47

CS 112 Introduction to Programming

CS 112 Introduction to Programming. User-Defined Data Types: Examples Yang (Richard) Yang Computer Science Department Yale University 308A Watson, Phone: 432-6400 Email: yry@cs.yale.edu. Admin. PS6 (Sukoku) questions Friday ’ s class.

hhouchens
Télécharger la présentation

CS 112 Introduction to Programming

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. CS 112 Introduction to Programming User-Defined Data Types: Examples Yang (Richard) Yang Computer Science Department Yale University 308A Watson, Phone: 432-6400 Email: yry@cs.yale.edu

  2. Admin • PS6 (Sukoku) questions • Friday’s class

  3. Recap: Design and Implementation Methodology: Procedural Based • Design (goal oriented) • top-down stepwise goal-drivenmethod decomposition • methods designed are those needed for the current goal • verb driven • Program implementation and testing • bottom-up

  4. Recap: Design and Implementation Methodology: Object-Oriented • Design • Identify objectsthat are part of the problem domain or solution • Each object has state (variables) • Each object has behaviors (methods) • Often do not consider one specific goal, but rather a context • noun driven

  5. Side-by-Side Comparison Object-oriented Function-oriented public class DrawRocket{ public static void main(String args[]){ for (int size = 3; size < 10; size++){ drawRocket(size); } } public static void drawRocket(int scale){ printCap(scale); ... } ... public static void printCap(int scale){ ... } } public class RocketDrawing{ public static void main(String args[]){ for (int size = 3; size < 10; size++){ Rocket curRocket = new Rocket(size); curRocket.draw(); } } } public class Rocket{ public int rocketSize; public Rocket(int rocketSize){ this.rocketSize = rocketSize; } public void draw(){ printCap(); ... } ... public void printCap(){ ... } }

  6. Recap: Class Definition Components • Variables • fields (instance variables per object) • static variables (shared by all objects) • Methods • static methods (method usable with or without object) • Can access only static variables • instance methods (can be used only on objects; can access both static and instance variables) • Constructors • Accessors (do not change object state) • Mutators (modify object state)

  7. Point class: Variables public class Point { // fields (instance variables, attributes) int x; int y; // static variables shared by all objects static int numPoints = 0;

  8. Point class: Constructors public class Point { … // constructors public Point(int x, int y) { this.x = x; this.y = y; numPoints ++; // a shared variable to // keep track of all // Points created. } public Point() { this(0, 0); }

  9. Point class: Static Methods public class Point { … // static methods: // cannot access any instance variables // because one may call Point.readpoint(input) // which has no implicit parameter public static Point readPoint(Scanner scan) { Point p = new Point(); p.x = scan.nextInt(); p.y = scan.nextInt(); return p; } public static int totalPoints() { return numPoints; }

  10. Point class: Instance Methods // mutators public void translate(int dx, int dy) { x = x + dx; y = y + dy; } public void setLocation(int x, int y) { this.x = x; this.y = y; } // accessors public double distanceFromOrigin() { return Math.sqrt(x * x + y * y); } public String toString() { return "(" + x + ", " + y + ")“; } public void draw() { StdDraw.filledCircle(x, y, 3); StdDraw.textLeft(x, y, toString() ); } }

  11. Point class as blueprint Point class state:int x, y behavior:translate(int dx, int dy)draw() … • The class (blueprint) will describe how to create objects. • Each object will contain its own data and methods. Point object #1 state:x = 5, y = -2 behavior:translate(int dx, int dy)draw()… Point object #2 state:x = -245, y = 1897 behavior:translate(int dx, int dy)draw()… Point object #3 state:x = 18, y = 42 behavior:translate(int dx, int dy)draw()…

  12. Outline • Admin and recap • Defining classes • Motivation and basic syntax • Examples

  13. Design and Implementation Methodology: Object-Oriented • Design • Identify objects (nouns) and their behaviors • Often do not consider one specific goal, but rather a context • Often lead to more reusable, extensible software

  14. Example 1: A Coin Class • We define a Coin class to model a coin in heads-tails games • Design questions: • State: what field(s) do we need to represent the state of a coin? • face, an integer (or boolean) that represents the current face • Operations: what are some common behaviors/operations of a coin in a game context? • a Coin constructor, to set up the object • a isHeadsmethod, to return if face is HEADS • a toString method, to return a string description of the current state • a flip method, to flip the coin • Q: introduce a setFace() method? See Coin.java, CountFlips.java, FlipRace.java

  15. class Coin coin1: Coin coin2: Coin intface; face = 0 face = 1 Instance Data: The Two Coins in FlipRace

  16. Example 2: The BankAccount Class • We define an BankAccount class to model a bank account • Design questions: • State: what field(s) do we need to represent the state of a bank acct? • acctNumber,an integer • acctName, a string • balance, an integer • Behaviors/operations: what are some common behaviors of a bank account in a simple banking context? • A constructor, to set up the object • a getBalance method, to return balance • a toString method, to return a string description of the current state • a withdraw method, to withdraw from the account • a deposit method, to deposit into the account • a addInterest method, to add interest See BankAccount.java, Transactions.java

  17. public class BankAccount { final double RATE = 0.035; long acctNumber; String acctName; double balance; public BankAccount (String owner, long account, double initial) { acctName = owner; acctNumber = account; balance = initial; } public double deposit (double amount) { balance = balance + amount; return balance; } … } public static void main (String[] args) { BankAccount aliceAcct = new BankAccount (“Alice", 11111, 100.00); BankAccount bobAcct = new BankAccount (“Bob", 22222, 200.00); BankAccount charlesAcct = new BankAccount (“Charles", 33333, 300.00); bobAcct.deposit (30.00); … } Example 2: Account and Transactions

  18. aliceAcct: BankAccount bobAcct: BankAccount charlesAcct: BankAccount aliceAcct: BankAccount bobAcct: BankAccount charlesAcct: BankAccount acctNumber = 11111 acctName = “Alice” balance = 100.00 acctNumber = 22222 acctName = “Bob” balance = 200.00 acctNumber = 33333 acctName = “Charles” balance = 300.00 acctNumber = 11111 acctName = “Alice” balance = 100.00 acctNumber = 22222 acctName = “Bob” balance = 230.00 acctNumber = 33333 acctName = “Charles” balance = 300.00 Example 2: The Three BankAccount Objects in Transactions After bobAcct.deposit (30.00);

  19. Example 3: The Ball Class • We define a Ball class to model self-bouncing balls

  20. Example 3: The Ball Class • Design questions: • State: what field(s) do we need to represent the state of a self-bouncing ball? • rx, ry, current position • vx, vy, speed • color, current color • left, right, bottom, top:cage (boundaries) • Behaviors/operations: what are some common behaviors of a self-bouncing ball? • A default constructor, to set up a random ball in unit square • A constructor, to set up a ball with given parameters • A movemethod, to update position • A drawmethod, to display See Ball.java, BouncingBalls.java

  21. Example 3: Bouncing Ball in Unit Square publicclass Ball { double rx, ry; double vx, vy; double radius; public Ball() { rx = ry =0.5; vx =0.015- Math.random()*0.03; vy =0.015- Math.random()*0.03; radius =0.01 + Math.random()*0.01; } public void move() { if((rx + vx >1.0)||(rx + vx <0.0)) vx =-vx; if((ry + vy >1.0)||(ry + vy <0.0)) vy =-vy; rx = rx + vx; ry = ry + vy; } public void draw() { StdDraw.filledCircle(rx, ry, radius); } } Ball.java instance variables constructor bounce methods

  22. Object References • Allow client to manipulate an object as a single entity. • Essentially a machine address (pointer). addr value 100 0 101 0 102 0 Ball b1 =new Ball(); b1.move(); b1.move(); Ball b2 =new Ball(); b2.move(); b2 = b1; b2.move(); 103 0 104 0 105 0 106 0 107 0 108 0 109 0 110 0 111 0 112 0 main memory(64-bit machine)

  23. 0.50 0.50 0.05 0.01 0.03 Object References addr value • Allow client to manipulate an object as a single entity. • Essentially a machine address (pointer). 100 0 101 0 102 0 Ball b1 =new Ball(); b1.move(); b1.move(); Ball b2 =new Ball(); b2.move(); b2 = b1; b2.move(); b1 103 0 100 104 0 105 0 106 0 107 0 108 0 109 0 110 0 111 0 112 0 registers main memory(64-bit machine)

  24. 0.55 0.51 Object References addr value • Allow client to manipulate an object as a single entity. • Essentially a machine address (pointer). 100 0.50 101 0.50 102 0.05 Ball b1 =new Ball(); b1.move(); b1.move(); Ball b2 =new Ball(); b2.move(); b2 = b1; b2.move(); b1 103 0.01 100 104 0.03 105 0 106 0 107 0 108 0 109 0 110 0 111 0 112 0 registers main memory(64-bit machine)

  25. 0.60 0.52 Object References addr value • Allow client to manipulate an object as a single entity. • Essentially a machine address (pointer). 100 0.55 101 0.51 102 0.05 Ball b1 =new Ball(); b1.move(); b1.move(); Ball b2 =new Ball(); b2.move(); b2 = b1; b2.move(); b1 103 0.01 100 104 0.03 105 0 106 0 107 0 108 0 109 0 110 0 111 0 112 0 registers main memory(64-bit machine)

  26. 0.50 0.50 0.07 0.04 0.04 Object References addr value • Allow client to manipulate an object as a single entity. • Essentially a machine address (pointer). 100 0.60 101 0.52 102 0.05 Ball b1 =new Ball(); b1.move(); b1.move(); Ball b2 =new Ball(); b2.move(); b2 = b1; b2.move(); b1 103 0.01 100 104 0.03 105 0 b2 106 0 107 107 0 108 0 109 0 110 0 111 0 112 0 registers main memory(64-bit machine)

  27. 0.57 0.54 Object References addr value • Allow client to manipulate an object as a single entity. • Essentially a machine address (pointer). 100 0.60 101 0.52 102 0.05 Ball b1 =new Ball(); b1.move(); b1.move(); Ball b2 =new Ball(); b2.move(); b2 = b1; b2.move(); b1 103 0.01 100 104 0.03 105 0 b2 106 0 107 107 0.50 108 0.50 109 0.07 110 0.04 111 0.04 112 0 registers main memory(64-bit machine)

  28. Object References addr value • Allow client to manipulate an object as a single entity. • Essentially a machine address (pointer). 100 0.60 101 0.52 102 0.05 Ball b1 =new Ball(); b1.move(); b1.move(); Ball b2 =new Ball(); b2.move(); b2 = b1; b2.move(); b1 103 0.01 100 104 0.03 105 0 b2 106 0 100 107 0.57 108 0.54 109 0.07 110 0.04 Data stored in 107 – 111 for bit recycler (garbage collection). 111 0.04 112 0 registers main memory(64-bit machine)

  29. 0.65 0.53 Object References addr value • Allow client to manipulate an object as a single entity. • Essentially a machine address (pointer). 100 0.60 101 0.52 102 0.05 Ball b1 =new Ball(); b1.move(); b1.move(); Ball b2 =new Ball(); b2.move(); b2 = b1; b2.move(); b1 103 0.01 100 104 0.03 105 0 b2 106 0 100 107 0.57 108 0.54 109 0.07 110 0.04 111 0.04 Moving b2 also moves b1 since they are aliases that reference the same object. 112 0 registers main memory(64-bit machine)

  30. Creating Many Objects • Each object is a data type value. • Use new to invoke constructor and create each one. publicclass BouncingBalls { publicstaticvoid main(String[] args) { int N = Integer.parseInt(args[0]); Ball balls[]=new Ball[N]; for(int i =0; i < N; i++) balls[i]=new Ball(); while(true) { StdDraw.clear(); for(int i =0; i < N; i++) { balls[i].move(); balls[i].draw(); } StdDraw.show(20); } } } create and initializeN objects animation loop

  31. Example 4: Continuous Line Graph • What is a base class to allow drawing of continuous line graphs? http://en.wikipedia.org/wiki/Turtle_graphics

  32. Example: Turtle • We define a Tutle class to keep track of drawing turtle (cursor) • Design questions: • State: what field(s) do we need to represent the state of a drawing turtle? • x,y, current position • angle: the current drawing direction • Operations: what are some common behaviors/operations on a Turle to allow flexible drawing? • A Turtle constructor, to set up the object • A goForward( stepSize) method • a turnLeft( angle ) method

  33. Turtle Graphics publicclass Turtle { double x, y;// turtle is at (x, y) double angle;// facing this direction public Turtle(double x0,double y0,double a0) { x = x0; y = y0; angle = a0; } publicvoid turnLeft(double delta) { angle += delta; } publicvoid goForward(double d) { double oldx = x; double oldy = y; x += d * Math.cos(Math.toRadians(angle)); y += d * Math.sin(Math.toRadians(angle)); StdDraw.line(oldx, oldy, x, y); } … }

  34. N-gon What is the angle of each turn? angle = 360/ N What is the initial degree? angle / 2 3 1440 7 34

  35. N-gon publicclass Ngon { publicstaticvoid main(String[] args) { int N = Integer.parseInt(args[0]); double angle = 360.0/ N; Turtle turtle =new Turtle(0.5,0, angle/2.0); double step = Math.sin(Math.toRadians(angle/2.0)); for(int i =0; i < N; i++) { turtle.goForward(step); turtle.turnLeft(angle); } } } 3 1440 7 35

  36. Spira Mirabilis publicclass Spiral { publicstaticvoid main(String[] args) { int N = Integer.parseInt(args[0]); double decay = Double.parseDouble(args[1]); double angle = 360.0/ N; double step = Math.sin(Math.toRadians(angle/2.0)); Turtle turtle =new Turtle(0.5,0, angle/2.0); for(int i =0; i <10* N; i++) { step /= decay; turtle.goForward(step); turtle.turnLeft(angle); } } } 36

  37. Spira Mirabilis publicclass Spiral { publicstaticvoid main(String[] args) { int N = Integer.parseInt(args[0]); double decay = Double.parseDouble(args[1]); double angle = 360.0/ N; double step = Math.sin(Math.toRadians(angle/2.0)); Turtle turtle =new Turtle(0.5,0, angle/2.0); for(int i =0; i <10* N; i++) { step /= decay; turtle.goForward(step); turtle.turnLeft(angle); } } } 1440 1.00004 3 1.2 3 1.0 1440 1.0004 37

  38. Spira Mirabilis in Nature 38

  39. Caution • René Magritte. "This is not a pipe." • Java. This is not a Turtle. • OOP. Natural vehicle for studying abstract models of the real world. TurlemyTurtle=new Turtle(0.5,0, 45); myTurle.turnLeft( 90 );

  40. Example 5: A Complex Class • A complex number (a + bi) is a quintessential mathematical abstraction • (a + bi) + (c + di) = a + c + (b + d)i • (a + bi) x(c + di) = ac - bd+ (ad + bc)i • Many applications of complex numbers • Fractals. • Impedance in RLC circuits. • Signal processing and Fourier analysis. • Control theory and Laplace transforms. • Quantum mechanics and Hilbert spaces. a = 3 + 4i, b = -2 + 3i a + b = 1 + 7i ab = -18 + i | a | = 5

  41. Argos Antennas 41

  42. A Complex Class • Design questions: • State: what field(s) do we need to represent the state of a complex number? • re, a number representing the real part • im, a number representing the imaginary part • Behaviors: what are some common behaviors of a complex number? • a Complex constructor, to set up the object • A abs method, to return the magnitude • a toString method, to return a string description of a complex number • Mathematical operations such as +, -, * • a plus method to add current complex number with another complex number • a times method to multiply current complex number with another complex number • …

  43. The Complex Class: Design Question public class Complex { double re; double im; public Complex(double real,double imag) { re = real; im = imag; } public ?? plus(Complex b) { … } … • What is the return type of plus? • Should plus change the state of the number

  44. The Consistency (Familiarity) Design Principle • Suppose a, b, and c are standard numbers (Complex numbers are numbers after all) • Does a + b (think a.+(b) ) change a? • no • What is the return of a + b (think a.+(b)? • The value of a + b so that we can write a + b + c • State (no)change and return type of plus public Complex plus(Complex b) { double real = re + b.re; double imag = im + b.im; returnnew Complex(real,imag); }

  45. Complex.java public class Complex { double re; double im; public Complex(double real,double imag) { re = real; im = imag; } public String toString() { return re +" + "+ im +"i"; } publicdouble abs() { return Math.sqrt(re*re + im*im); } public Complex plus(Complex b) { double real = re + b.re; double imag = im + b.im; returnnew Complex(real,imag); } public Complex times(Complex b) { double real = re * b.re – im * b.im; double imag = re * b.im + im * b.re; returnnew Complex(real,imag); } } instance variables constructor refers to b's instance variable creates a Complex object,and returns a reference to it methods

  46. Immutability: Advantages and Disadvantages • Immutable data type. Object's state does not change once constructed. • Complex is an example of Immutable objects. String defined by Java is another example. • Advantages. • Avoid aliasing bugs. • Makes program easier to debug. • Limits scope of code that can change values. • Pass objects around without worrying about modification. • Disadvantage. New object must be created for every value.

  47. A Simple Client publicstaticvoid main(String[]args) { Complex a =new Complex( 3.0,4.0); Complex b =new Complex(-2.0,3.0); Complex c = a.times(b); System.out.println("a = "+a.toString() ); System.out.println("b = "+b.toString() ); System.out.println("c = "+c.toString() ); } % java TestClient a = 3.0 + 4.0i b = -2.0 + 3.0i c = -18.0 + 1.0i

More Related