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Input and Output

Input and Output
1.5 Input and Output Introduction to Programming in Java: An Interdisciplinary Approach · Robert Sedgewick and Kevin Wayne · Copyright © 2002–2010 · 2/14/11 7:49 AM Input and Output Input devices. Keyboard Mouse Hard drive Network Digital camera Microphone Output devices. Display Network Speakers Hard drive MP3 Player Printer Goal. Java programs that interact with the outside world. 2 Input and Output Input devices. Keyboard Mouse Hard drive Network Digital camera Microphone Output devices. Display Network Speakers Hard drive MP3 Player Printer Our approach.   Define Java libraries of functions for input and output.   Use operating system (OS) to connect Java programs to: file system, each other, keyboard, mouse, display, speakers. 3 Terminal Terminal. Application where you can type commands to control the operating system. Mac OS X Microsoft Windows 4 CommandLine Input and Standard Output Commandline input. Read an integer N as commandline argument. Standard output.   Flexible OS abstraction for output.   In Java, output from System.out.println() goes to standard output.   By default, standard output is sent to Terminal. public class RandomSeq public static void main(String args) int N = Integer.parseInt(args0); for (int i = 0; i N; i++) System.out.println(Math.random()); java RandomSeq 4 0.9320744627218469 0.4279508713950715 0.08994615071160994 0.6579792663546435 5 Old Bird's Eye View 6 New Bird's Eye View 7 Standard Input and Output CommandLine Input vs. Standard Input Commandline inputs.   Use commandline inputs to read in a few user values.   Not practical for many user inputs.   Input entered before program begins execution. Standard input.   Flexible OS abstraction for input.   By default, standard input is received from Terminal window.   Input entered while program is executing. 9 Standard Input and Output Standard input. StdIn is library for reading text input. Standard output. StdOut is library for writing text output. libraries developed for this course (also broadly useful) 10 Standard Input and Output To use. Download and from booksite, and put in working directory (or use classpath). see booksite public class Add public static void main(String args) StdOut.print("Type the first integer: "); int x = StdIn.readInt(); StdOut.print("Type the second integer: "); int y = StdIn.readInt(); int sum = x + y; StdOut.println("Their sum is " + sum); java Add Type the first integer: 1 Type the second integer: 2 Their sum is 3 11 Averaging A Stream of Numbers Average. Read in a stream of numbers, and print their average. public class Average public static void main(String args) double sum = 0.0; // cumulative total int n = 0; // number of values while (StdIn.isEmpty()) double x = StdIn.readDouble(); sum = sum + x; n++; java Average 10.0 5.0 6.0 StdOut.println(sum / n); 3.0 7.0 32.0 Ctrld 10.5 Ctrld for OS X/Linux/Unix/DrJava Ctrlz for Windows Key point. Program does not limit the amount of data. 12 Redirection and Piping Redirecting Standard Output Redirecting standard output. Use OS directive to send standard output to a file for permanent storage (instead of terminal window). java RandomSeq 1000 data.txt redirect stdout 14 Redirecting Standard Input Redirecting standard input. Use OS directive to read standard input from a file (instead of terminal window). more data.txt 0.5475375782884312 0.4971087292684019 0.23123808041753813 … redirect stdin java Average data.txt 0.4947655567740991 15 Connecting Programs Piping. Use OS directive to make the standard output of one program become the standard input of another. pipe stdout of RandomSeq to stdin of Average java RandomSeq 1000000 java Average 0.4997970473016028 java RandomSeq 1000000 java Average 0.5002071875644842 16 Standard Drawing Standard Drawing Standard drawing. StdDraw is library for producing graphical output. library developed for this course (also broadly useful) 19 Standard Draw Standard drawing. We provide library StdDraw to plot graphics. To use. Download and put in working directory. public class Triangle public static void main(String args) double t = Math.sqrt(3.0) / 2.0; StdDraw.line(0.0, 0.0, 1.0, 0.0); StdDraw.line(1.0, 0.0, 0.5, t); StdDraw.line(0.5, t, 0.0, 0.0); StdDraw.point(0.5, t/3.0); (, 3) java Triangle (0, 0) (1, 0) 20 Data Visualization Plot filter. Read in a sequence of (x, y) coordinates from standard input, and plot using standard drawing. public class PlotFilter public static void main(String args) rescale coordinate double xmin = StdIn.readDouble(); system double ymin = StdIn.readDouble(); double xmax = StdIn.readDouble(); double ymax = StdIn.readDouble(); StdDraw.setXscale(xmin, xmax); StdDraw.setYscale(ymin, ymax); while (StdIn.isEmpty()) read in points, and plot them double x = StdIn.readDouble(); double y = StdIn.readDouble(); StdDraw.point(x, y); 21 Data Visualization bounding box more USA.txt coordinates of 669905.0 247205.0 1244962.0 490000.0 13,509 US cities 1097038.8890 245552.7780 1103961.1110 247133.3330 1104677.7780 247205.5560 ... java PlotFilter USA.txt 22 Plotting a Function double x = new doubleN+1; double y = new doubleN+1; for (int i = 0; i = N; i++) xi = Math.PI i / N; yi = Math.sin(4xi) + Math.sin(20xi); StdDraw.setXscale(0, Math.PI); StdDraw.setYscale(2.0, +2.0); for (int i = 0; i N; i++) StdDraw.line(xi, yi, xi+1, yi+1); (π, 2) (0, 2) y = sin 4x + sin 20x, x " 0, 23 Chaos Game Chaos game. Play on equilateral triangle, with vertices R, G, B.   Start at R.   Repeat the following N times: –  pick a random vertex –  move halfway between current point and vertex –  draw a point in color of vertex B: (, 3) Q. What picture emerges 2 B B G R B G … 5 1 3 6 4 0 G: (1, 0) R: (0, 0) 24 Chaos Game public class Chaos public static void main(String args) int T = Integer.parseInt(args0); 3 double cx = 0.000, 1.000, 0.500 ; (avoid hardwired constants like this) double cy = 0.000, 0.000, 0.866 ; double x = 0.0, y = 0.0; for (int t = 0; t T; t++) int r = (int) (Math.random() 3); x = (x + cxr) / 2.0; y = (y + cyr) / 2.0; between 0 and 2 StdDraw.point(x, y); 25 Chaos Game Easy modification. Color point according to random vertex chosen using StdDraw.setPenColor(StdDraw.RED) to change the pen color. B java Chaos 10000 R G Sierpinski triangle 26 Barnsley Fern Barnsley fern. Play chaos game with different rules. probability new x new y 2 .50 .27y 15 .14x + .26y + .57 .25x + .22y .04 13 .17x .21y + .41 .22x + .18y + .09 70 .78x + .03y + .11 .03x + .74y + .27 Q. What does computation tell us about nature Q. What does nature tell us about computation th 20 century sciences. Formulas. st 21 century sciences. Algorithms 29 Animation Animation loop. Repeat the following:   Clear the screen.   Move the object.   Draw the object.   Display and pause for a short while. Ex. Bouncing ball.   Ball has position (rx, ry) and constant velocity (vx, vy).   Detect collision with wall and reverse velocity. (+1, +1) (vx, vy) (rx, ry) (1, 1) 30 Bouncing Bal l public class BouncingBall public static void main(String args) position double rx = .480, ry = .860; constant velocity double vx = .015, vy = .023; radius double radius = .05; StdDraw.setXscale(1.0, +1.0); rescale coordinates StdDraw.setYscale(1.0, +1.0); while(true) if (Math.abs(rx + vx) + radius 1.0) vx = vx; bounce if (Math.abs(ry + vy) + radius 1.0) vy = vy; rx = rx + vx; update position ry = ry + vy; clear background StdDraw.setPenColor(StdDraw.GRAY); StdDraw.filledSquare(0.0, 0.0. 1.0); StdDraw.setPenColor(StdDraw.BLACK); draw the ball StdDraw.filledCircle(rx, ry, radius);; turn on animation mode: display and pause for 50ms 31 Bouncing Ball Demo java BouncingBall 32 Special Effects Images. Put .gif, .png, or .jpg file in the working directory and use StdDraw.picture() to draw it. Sound effects. Put .wav, .mid, or .au file in the working directory and use to play it. Ex. Modify BouncingBall to display image and play sound upon collision.   Replace StdDraw.filledCircle() with: StdDraw.picture(rx, ry, "earth.gif");   Add following code upon collision with wall:"boing.wav"); 33 Deluxe Bouncing Ball Demo java DeluxeBouncingBall 34 Bouncing Ball Challenge Q. What happens if you call StdDraw.filledSquare() once before loop (instead of inside) java DeluxeBouncingBall 35 Colliding Balls Challenge. Add elastic collisions. java CollidingBalls 100 36 Nbody Simulation Challenge. Add gravity. java NBody planets.txt 37
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