Transcript Lecture 12 Slides

Programming for Beginners
Lecture 12: Programming Project
Martin Nelson
Elizabeth FitzGerald
Revision of session 11
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Java has in-built techniques for handling errors:
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Place ‘dangerous’ code inside a try statement.
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If this code generates an error, it throws an exception.
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Immediately after the try statement, we have a catch statement,
which contains instructions for how to handle various types of
exception.
File I/O can be done using the class RandomAccessFile
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Mode can be “r” (read-only) or “rw” (read-write).
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All file I/O must be error-trapped, i.e. inside a try statement.
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Useful method for reading data: readLine
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Useful method for writing data: writeBytes
Session 12 – aims and objectives
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Programming project!
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Using all the concepts which we’ve covered in the course
so far:
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Software design – pen & paper!!
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Pseudocode.
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Coding, bit by bit.
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Software testing.
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Successive refinement.
Programming Project
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Task: Create an address book program, capable of
storing the contact details of a number of your friends.
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Make a class called “Person”, with variables to store
name, address, phone number and email address.
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Your program should store a number of friends in an
array.
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Ask the user to choose between adding new friends,
updating old friends’ information, or search for a friend by
name.
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Store the contact info in a text file.
Programming Project
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This task will take some time – there is a lot to do!
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Break the task down into smaller chunks...
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Create the Person class.
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Store some people in an array manually.
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Add User input.
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Add methods to manipulate data.
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Add File I/O.
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Remember: Pen & paper first!
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Pseudocode!
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Test the code after every step!
How do I exit?
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You may like to loop your code, repeatedly asking the
user to add friends, update contacts, search for people
etc. until they get bored...
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Can use a perpetual loop to do this...
while(true){ do_stuff };
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If you do this, make sure you give the user the choice to
quit the program.
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To end the program neatly:
System.exit(0);
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Don’t worry about this until everything else in your code
works properly!
The File Class – 1
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You may find that a convenient way to update your
contacts file is to delete the old version, and re-populate
the list from scratch.
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The File class contains a number of methods for
manipulating files. For example, to delete the file
contacts.txt:
File myFile = new File(“contacts.txt”);
myFile.delete();
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The File class also contains methods for testing read/write
access to a given file/directory, and much more. See the
documentation for more details.
The File Class – 2
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Do not confuse File with RandomAccessFile!
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File class:
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manipulating files and directories
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testing for existence
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testing read/write access
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creating/deleting files/directories
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extracting file properties.
RandomAccessFile class:
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reading data from files
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writing data to files.
Coming up in Sessions 13-15
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Some new languages, other than Java!
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Session 13: A brief introduction to C++
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Session 14: A brief introduction to scripting languages.
Session 15: Overview of some more-advanced concepts
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Some ideas that we should be aware of for efficient coding.
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Some more interesting java tasks, e.g. graphics!
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Where to go next? Future C++ and Java programming courses.