CPSC-112 Introduction to Programming

Transcription

1 CPSC-112 Introduction to Programming StdAudio and Object-Oriented Programming Friday, March 28th 2014

2 StdAudio

3 StdAudio Sound is the perception of vibrations in our eardrums.

4 Digital Audio Digital audio samples the analog, continuous sound wave some number of times per second. When these samples are played in succession, like a picture flipbook, it approximates the continuous sound. Audio CD

5 Digital Audio in Java StdAudio is a Java library for producing sound waves and playing.wav audio files. 5 library developed from book:

6 Musical Tone Concert A Play Concert A for 1.5 seconds using StdAudio. double hz = 440.0; double seconds = 1.5; int SAMPLE_RATE = 44100; int N = (int) (seconds * SAMPLE_RATE); double[] a = new double[n+1]; for (int i = 0; i <= N; i++) { a[i] = Math.sin(2 * Math.PI * i * hz / SAMPLE_RATE); StdAudio.play(a);

7 PlayThatTune Read in pitches and durations from standard input and sonify with StdAudio.

8 PlayThatTune public class PlayThatTune { public static void main(string[] args) { Scanner console = new Scanner( System.in ); while (console.hasnextint()) { int pitch = console.nextint(); double seconds = console.nextdouble(); double hz = * Math.pow(2, pitch / 12.0); int SAMPLE_RATE = 44100; Same as before int N = (int) (seconds * SAMPLE_RATE); double[] a = new double[n+1]; for (int i = 0; i <= N; i++) { a[i] = Math.sin(2 * Math.PI * i * hz / SAMPLE_RATE); StdAudio.play(a);

9 StdAudio Library StdAudio.java in Eclipse PS7 released today Uses StdAudio Pair programming allowed When should we do the walk-through?

10 Object-Oriented Programming

11 OOP High-Level Programming: A list of statements or commands Physical world objects OOP Insight: encapsulate a list of statements into an object. Use one main object to trigger the functionality within other objects.

12 On the path to OOP NBody.java StdDraw.java public class NBody { public class StdDraw { public static void main(string [] args) { public static void draw(...) {... StdDraw.draw(...);... // end draw StdDraw.draw(...); // end class // end main // end class

13 Properties of StdDraw Example StdDraw is full of static methods The method carries no internal state Parameters are the only output influence In contrast, OOP: Encapsulate functionality like draw(...) But support internal or inherent state

14 Our First Object Point.java Remember, scoping. These variables are accessible everywhere within the outer curly braces. public class Point { public int x; public int y; Point(int xcoord, int ycoord) { x = xcoord; y = ycoord; // end class Constructor Special method, no return type return type and Class type are the same. Code: Point pt; pt = new Point(1, 2); // Declare a variable named pt of class type Point. // pt doesn't have an actual object in memory yet. // Now pt stores the location of a Point object in memory.

15 Creating an Object Point pt; // Declare a variable named pt of class type Point. // pt doesn't have an actual object in memory yet. Computer's memory pt = new Point(1, 2); pt??? public class Point {... // end class We've created an instance of the Point class, and we use pt to refer to that instance in the future.

16 Using an Object Point.java public class Point { public int x; public int y; Point(int xcoord, int ycoord) { x = xcoord; y = ycoord; // end class Code: Point pt = new Point(1, 2); System.out.println(pt.x + + pt.y); // Prints 1 2 When we refer to pt.x, that's a variable. What is its type?

17 Making Our Object Accessible Point.java public class Point { private int x; private int y; Make class variables private Point(int xcoord, int ycoord) { x = xcoord; y = ycoord; public int getx() { return x; public int gety() { return y; // end class Add accessors for retrieval

18 Making Our Object Accessible Code: Point pt = new Point(1, 2); System.out.println(pt.x + + pt.y); // Won't work!! System.out.println(pt.getX() + + pt.gety()); // The power of classes Reusability Point otherpoint = new Point(3, 4); System.out.println(pt.getX() otherpoint.getx() + = + (pt.getx() + otherpoint.getx())); // We can approximate a Box Point topleft = new Point(-1, Point botright = new Point(1, int width = botright.getx() int height = topleft.gety() System.out.println( width= + around the origin w/ two Points. 1); -1); topleft.getx(); botright.gety(); width + height= + height);

19 Objects, generally MyClass.java public class MyClass { // Instance variables. // Remember: One copy of each variable per instance. private int y;... // Constructor use parameters for setting initial values. MyClass (...) {... // Accessors get/set instance variables. public void sety(int yval) { y = yval; // Functionality (covered next). // end class

20 Object Functionality public class Point { private int x; private int y; // Constructor, accessors // Measure the distance between // this Point and another Point. public double distance(point pt) { int xdist = pt.getx() - this.x; int ydist = pt.gety() - this.y; int sum = (xdist * xdist) + (ydist * ydist); return Math.sqrt((double)sum); // end class Point pt1 = new Point(1, 2); Point pt2 = new Point(23, 30); double dist = pt1.distance(pt2); The class can define arbitrary methods that use other instances of the class. Notice this refers to the instance variables of the object on which the method is invoked. Which Point uses this here?

21 Object State public class Point { private int x; private int y; // Constructor, accessors // Moves this Point to the right // until it is a multiple of 10. public void moverighttomult10() { while (this.x % 10!= 0) { this.x++; // end class Point pt1 = new Point(1, 2); System.out.println(pt1.getX()); pt1.moverighttomult10(); System.out.println(pt1.getX()); // Prints 1 // Prints what? This method modifies the internal state of the object.

22 Rational Number Example RationalNumber.java in Eclipse