Click to edit Master title style Click to edit Master text styles Second level Third level Fourth level Fifth level 1 Files Section 2.13, Section 8.8

Click to edit Master title style Click to edit Master text styles Second level Third level Fourth level Fifth level 2 Files To use files, use File class File class can’t read/write To read/write files, use Scanner/PrintWriter classes File input can be text-based (what we’ll do), stream-based

Click to edit Master title style Click to edit Master text styles Second level Third level Fourth level Fifth level 3 Text Input Use the Scanner class import java.util.Scanner; java.io.File; Put Scanner activity within try { …} catch (Exception e) {…} Tie object to File object and diskfile name Use next to get next String, nextInt to get nextInt, etc. [Must know order of input] Close the scanner object.

Click to edit Master title style Click to edit Master text styles Second level Third level Fourth level Fifth level 4 Text Input try { Scanner s = new Scanner (new File("filename.txt")); while (s.hasNext( )) // read to EOF { String firstS = s.next( ); int secondI = s.nextInt( ); double thirdD = s.nextDouble( ); // do something with what you just read } catch (Exception except) { // do what happens when things go tragically awry System.out.println("Things went tragically awry"); System.exit(1); } you must have new File. you must put Scanner declaration in try- catch means input order is String, int, double for each record }

Click to edit Master title style Click to edit Master text styles Second level Third level Fourth level Fifth level 5 Text output Use the PrintWriter class. Import java.io.PrintWriter Put inside try { …} catch (Exception e) {…} Tie PrintWriter object to diskfile name Use print, println to write to the object Close the FileWriter.

Click to edit Master title style Click to edit Master text styles Second level Third level Fourth level Fifth level 6 Text output try { PrintWriter writer = new PrintWriter("name of file"); while(there is more text to write) {... writer.println(next piece of text);... } writer.close(); } catch(IOException e) { /* something went wrong with accessing the file */ }

Click to edit Master title style Click to edit Master text styles Second level Third level Fourth level Fifth level 7 Write a program to count number of lines in a file and write the number to an output file java countlines myinfile.txt myoutfile.txt would return 2 if file is: This is a file with two lines. myinfile.txt

Click to edit Master title style Click to edit Master text styles Second level Third level Fourth level Fifth level 8 import java.io.*; public class countlines { // all methods that do something inserted here public static void main(String[] args) { if (args.length != 2) { System.out.println ("to run, type: 'java countlines filein fileout'"); System.exit(1); } // create a new countline object with first arg as input file, second as output countlines cl = new countlines(args[0], args[1]); }

Click to edit Master title style Click to edit Master text styles Second level Third level Fourth level Fifth level 9 // constructor public countlines(String filein, String fileout) { int nbrLines = readfrom(filein); writeTo(fileout, nbrLines); } // write method public void writeTo(String fileout, int nbrLines) { PrintWriter outFile = new PrintWriter(new File(fileout)); fileout.println("The number of lines is " + nbrLines); fileout.close( ); }

Click to edit Master title style Click to edit Master text styles Second level Third level Fourth level Fifth level 10 Scanner Class: for reading files public int readfrom(String filein) { Scanner scanner; try { scanner = new Scanner(new File(filein)); while (scanner.hasNext) { String line = scanner.nextLine( ); // also next( ), nextInt( ), nextDouble( ) System.out.println(line); // for debugging only; countlines++; } return countlines; } catch (FileNotFoundException ex) { System.out.println("File not found...aborting program."); System.exit(1); } }

Click to edit Master title style Click to edit Master text styles Second level Third level Fourth level Fifth level 11 Console input: Section 2.13 Scanner class: Java 5 import java.util.*; class MyScanner { public MyScanner ( ) { Scanner scanner = new Scanner(System.in); System.out.println("Enter a number: "); int x = scanner.nextInt(); int y = scanner.nextInt(); System.out.println("The sum of " + x + " + " + y + " is " + (x+y)); }

Click to edit Master title style Click to edit Master text styles Second level Third level Fourth level Fifth level 12 File input using Scanner import java.util.*; import java.io.*; class MyScanner { public MyScanner ( ) { Scanner scanner; try { scanner = new Scanner(new File("infile.java")); int x = scanner.nextInt( ); int y = scanner.nextInt( ); System.out.println("The sum of " + x + " + " + y + " is " + (x+y)); } catch (FileNotFoundException ex) { System.out.println("File not found...aborting program."); System.exit(1); } }

Click to edit Master title style Click to edit Master text styles Second level Third level Fourth level Fifth level 13 Write a Payroll Program Write a program that reads in a file in the form first last hourlyrate hoursworked exempt, e.g,: Susie Jones N Johnny Jacob Y Jane White N And writes out information to an output file in the form: first last weeklypay, e.g., Susie Jones: Johnny Jacob: Jane White: Your program should get the filein and fileout names from the command line. Print the total payroll for the week in a terminal window. Pay should be figured in the following way: if the employee has worked no overtime, pay is number of hours * hourly rate. Otherwise, if the employee is not exempt, the pay is hourly rate * 40 + hourly rate * 1.5 * hours over 40. If the employee is exempt, the employee receives no overtime (so is paid for no more than 40 hours, less if the employee worked less).