Programming Heuristics Implications for tagcloud? Identify the - - PowerPoint PPT Presentation

Software Design 2.1

Programming Heuristics

 Identify the aspects of your application that vary

and separate them from what stays the same

• Take what varies and encapsulate it

 Program to an interface, not an implementation

• Specify behavior by name, not by working code

 Favor Composition over Inheritance

• Use "has-a" rather than "is-a"

 Classes and code should be open for extension, but

closed to modification

• The Open-Closed Principle

Software Design 2.2

Implications for tagcloud?

 What might change in going from release 0.9 to 1.0

to 2.0 in tag cloud

• Should we worry about future changes?
• Should we make things work now?
• Can we do both?

 Strategy pattern

• Algorithm varies independently from clients that

use it,

• What are the algorithms in tag cloud?

Software Design 2.3

Design patterns

“... describes a problem which occurs over and over again in our environment, and then describes the core of the solution to that problem, in such a way that you can use this solution a million times over, without ever doing it the same way twice”

Christopher Alexander, quoted in GOF

 Name

• good name is a handle for the pattern, builds vocabulary

 Problem

• when applicable, context, criteria to be met, design goals

 Solution

• design, collaborations, responsibilities, and relationships

 Forces and Consequences

• trade-offs, problems, results from applying pattern: help in

evaluating applicability

Software Design 2.4

Towards being a hacker

 See the hacker-faq (compsci 108 web page)

• Hackers solve problems and build things, and they

believe in freedom and voluntary mutual help. To be accepted as a hacker, you have to behave as though you have this kind of attitude yourself. And to behave as though you have the attitude, you have to really believe the attitude.

 The world is full of fascinating problems

• no one should have to solve the same problem twice
• boredom and drudgery are evil
• freedom is good
• attitude is no substitute for competence

You may not work to get reputation, but the reputation is a real payment with consequences if you do the job well.

Software Design 2.5

Aside: ethics of software

 What is intellectual property, why is it

important?

• what about FSF, GPL, copy-left, open source,
• what about money and monopolies

 What does it mean to act ethically and

responsibly?

• What about copying? stealing? borrowing?
• No harm, no foul? Is this a legitimate

philosophy?

• Can software developers make a difference

in the world?

Software Design 2.6

Richard Stallman

 Free Software movement

• Free as in speech
• Not Free as in beer

 Wrote emacs, gcc,gdb,…

• GNU's not Unix

 Grace Murray Hopper award,

Macarthur award, EFF Pioneer award,

Software Design 2.7

java.io.*

 What is a package? How are packages organized in

Java? How do you find how to use them?

• Reading API, reading books, writing code

 In Java there are lots of ways of reading, mostly

using InputStream and Reader abstract classes

• Corresponding Writer classes?

 These classes use the Decorator pattern

• Reading files? FileReader to BufferedReader
• How to read System.in line-by-line?
• See also java.util.Scanner , your friend!

Software Design 2.8

java.util.*

 Contains the collections framework, legacy

collection classes, event model, date and time facilities, internationalization, and miscellaneous utility classes (a string tokenizer, a random-number generator, and a bit array)

 From programmer's perspective the Collection

hierarchy provides data structures

• Lists, Sets, Maps of elements (and others)
• Your code must know how to play well with

collections

Software Design 2.9

Playing well with Collections

 Every object has an equals(..) method, contract?

• What does this return? How do you implement

it, what about apples and oranges?

• Default behavior? When to over-ride?

 If you override/over-ride equals, see hashCode()

• What does this return? Implementation issues?
• Good, bad, …?

Software Design 2.10

Loose coupling and collections

 How do you store data in tag cloud?

• What do you store?
• How do you access it?
• What are performance issues and trade-offs?

 Difference in storing into a Map versus storing into

a CloudCollector?

• What heuristics are in play?
• What do you do first?