20 Oct - Overview

1
20 Oct - Overview

• Homework 1
• Group-Id rule
• Notes on Java text file input/output
• Scanner class
• Printf (like C)

2
Homework 1

• http//pmik.petrsu.ru/pub/ourusoff/Intro to
  JSE/Home Work/
• due noon, Friday, 21 Oct
• email solution as (zipped) attachment to
• nourusoff_at_psu.karelia.ru
• Please send me
• 4 .jsp files that show the design of the original
  output table and each of the 3 modifications
• Extra credit 3 .jsp files that show the
  modification of the bad multiplication table to
  produce the 3 modifications

3
Group-ID Rule

• We frequently wish to process groups in a file
  sorted by group.
• Problem Census file is sorted on a household
  number. Data for each household is to be
  accumulated.
• Detailed problem statement
• System diagram
• Data structures for
• input - censusFile.jsp
• output - censusReport.jsp
• Composite data model showing correspondences
• Basic Program Structure - censusBasicStr.jsp
• List and allocate operations
• Produce elaborated program structure -
  censusElabStr.jsp
• Generate structure text or code
• Structure text
• Java code

4
Group ID Rule

• Group-id Rule If a structure contains a
  component that is a group of records all having
  the same value of a (usually sorted) identifier,
  then there must be an operation that stores the
  value of the identifier. This operation should
  be allocated once per group, at the beginning of
  the group.
• Design focuses on
• a static not a dynamic view of the problem
• data structures (objects), not on dynamic flow of
  control

5
Homework 2 (due 28 October)

• The Census household problem is modified as
  follows
• (The course page has a sample file,
  censusFile.txt in the HW2 folder. Test your
  program with this file.)
• The census text file has a city code in positions
  8-10. Accumulate the total number of males and
  females as well as the average household size in
  each city and produce the summary as before.
• Put sensible column headings in the report
  (Household Id, Males, Females, etc.)
• Use Scanner and printf for reading and writing.

6
Using the Scanner utility class

• Scanner is in the util package, not the lang
  package so you need to include the
  line  import.util.Scanner at the top of the
  class.
• To create a Scanner object and connect it to a
  file you must create a File object based on the
  name of that file. This can be done with one
  line Scanner s new Scanner( new
  File(census.txt"))Remember all programs are
  judged assuming the file is in the same directory
  as the compiled class file so do not put any path
  information on the file, just the file name. To
  use the file class you must include the
  line import.io.File at the top of your
  program.

7
Using the Scanner utility class (cont.)

• Unfortunately instantiating a File object can
  result in in an IOException and this is a checked
  exception so you either have to use a try-catch
  block or declare that the method that contains
  the code that generates the checked exception
  throws an IOException.
• In actual programming practice it would be much
  better to include a try-catch block, but for
  educational purposes and programming contest
  purposes it is much easier to simply declare that
  main throws an IOException.
• Thus the declaration of the main method looks
  like thispublic static void main(String
  args) throws IOException
• IOException must also be imported. This can
  either be done as a separate import
  statementimport java.io.IOExceptionor since
  the program now needs multiple classes from the
  io package we can use the wildcard import. Again,
  not the best programming practice, but for
  Olympiads, not a bad idea.import java.io.

8
Java I/O with Scanner and Formatter

• Java documentation
• Tutorial on printf
• Printf.demo.java
• Tutorial on Using Scanner for Input from Console
• ScanConsoleApp.java