CSC1401 Input and Output with Files

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CSC1401Input and Output (with Files)
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Learning Goals

• Computing concepts
• Input and output with files in Java
• Using the Scanner class for file input, and
  PrintWriter for output

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Recall

• import java.util. // needed for scanner
• class IOTesting
• public static void main(String args)
• Scanner scan new Scanner(System.in) i
  nt value scan.nextInt()

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Using Files for input

• Instead of System.in, we can specify a file
• Two differences
• We need to import java.io.
• Doing file input can lead to an exception if the
  type of data we are requesting doesnt match
  whats in the file

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Note the changes

• import java.util. // needed for scanner
• import java.io. // needed for file
• class FileIO
• public static void main(String args) throws
  Exception
• // throws exception is for file i/o
• Scanner sc new Scanner(System.in)Scanner
  sc2 new Scanner(new File("data.txt"))int i
  sc2.nextInt()

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Lets create a file and try

• Can use Notepad, or just about anything else
  besides MS Word
• Lets read in a bunch of scores into an array

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Reading several numbers from a file

• Scanner sc2 new Scanner(new File("data.txt"))
  int list new int10int count 0
• while (sc2.hasNextInt() count lt
  10) listcount sc2.nextInt() count
  count 1 for (int i 0 ilt counti)
• System.out.println("list
• i " listi)
• sc2.close() // when you open a file, you//
  should close it

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File Output

• Again, well change from System.out to something
  else

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An example with file output

• import java.io. // needed for file
• class IO
• public static void main(String args)
• throws Exception// throws exception is for
  file i/o int i 5 PrintWriter steveout
  new PrintWriter(
• new FileWriter("silly2.txt")) steveout.printl
  n(i " is the value") steveout.close()

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Summary

• We use Printwriter for output to a file (the
  Media Computation book has an alternate approach)
• We use a Scanner object for getting input from a
  file

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Reading Assignment

• Media Computation Chapter 12, Section 3 (but not
  section 12.3.3)