Java Introductory Course Part 3

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Java Introductory CoursePart 3

• Using
• And re-using Java!
• (Once and Once Only Principle)
• Programming to Interfaces
• Simon M. Lucas

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Session Objectives

• Further appreciate the benefits of Java
• Gain experience of some useful input / output
  methods, and some graphics classes
• Perform some simple data processing
• Learn to identify possible classes to simplify
  problem solutions and achieve greater re-use
• Practice writing re-usable code

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Why Java?

• Nice language easy to read
• E.g. keywords interface and extends
• Platform independent
• Easy to learn
• Great IDEs Intellij Idea, NetBeans, Eclipse
• Powerful API (class libraries) networking,
  graphics, threads, XML etc
• Can be run in secure mode good for remote code
  (applets etc)
• Tetris, SOFM

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Typical Features of a Modern IDE

• Allows easy re-factoring
• Great to use
• Short-cuts (e.g. psvm, sout)
• navigate to definition of current word
• Understand Java and JSP
• Code completion
• Method signatures
• Speeds up learning Java immensely!
• Auto code layout

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Whats hard about programming?

• Designing smart algorithms?
• E.g. inventing quicksort if we didnt already
  have it
• True but dont often need this
• Great deal is about modelling and organisation
• As we shall see
• Other tough things multi-threaded, distributed,
  persistence, web-based

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Program Structure

• Monolithic to Multi-Class Re-usable

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Exercise

• A file contains measurements from instances of
  several different types of specimen
• Each line consists of a specimen id followed by a
  number
• Write a program to calculate the number of values
  recorded, the mean and the s.d. for each
  experiment
• Print these statistics to standard output
• Look for any classes that could be re-used in
  other applications

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Sample DataLab Exercise

• 0 182
• 1 181
• 1 190
• 0 170
• 0 175
• (e.g. consider that 0Female, 1Male, and the
  second number on the line is the weight of that
  person in kilos)

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Class Discussion

• Working in small groups, discuss possible program
  designs to solve the above problem
• Implement and test your design
• Identify which parts of your program could be
  re-used in another application

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Bar Chart Exercise

• Consider the program (see lab) to draw a bar
  chart from an array of numbers
• Suppose now you want to offer a plug and play
  interface, so that third party developers can
  provide their own bar styles
• Design an interface for this, and provide a
  sample implementation (e.g. to draw faded or
  textured bars

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Summary

• I hope these introductory exercises have given
  you some idea about developing Java programs
• Some advice
• Keep each method simple
• Programming to interfaces aids re-use
• Keep classes tightly focussed more re-use
• Use a good IDE
• Enjoy!