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Input and Output

Input and Output
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Published Date:21-07-2017
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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 Command-Line Input and Standard Output Command-line input. Read an integer N as command-line 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 Command-Line Input vs. Standard Input Command-line inputs.   Use command-line 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 Ctrl-d 10.5 Ctrl-d for OS X/Linux/Unix/DrJava Ctrl-z 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