Savitch

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1/13/2003

• Savitch
• Chapter One
• And

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Business

• Reminders
• Join the list
• Submit information form
• Submit permission to post
• The forms are available on my web site

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• I think Ill start taking photos on today. Well
  see how it goes.
• The syllabus now has links to web pages for the
  two texts

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Chapter One

• The stuff I dont mention, Im assuming you
  already know. If not,

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Topics

• Java Byte-Code 10-12
• Object-Oriented Programming 17-23
• 1.4 A Taste of Java 25-40

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Java Byte-Code

• It creates independence
• If you have a Java Virtual Machine its
  software running on your computer, you can run a
  compiled Java program regardless of the type of
  machine on which it was compiled.
• Thats a biggie

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Interpreting

• Actually the program runs on the JVM.
• It is said to be interpreted.
• The JVM interprets the byte code and does the
  equivalent work on the host machine

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Object-Oriented Programming

• See Dennis Wixon Chapter 16
• There are things
• Objects nouns
• They do things to themselves or others
• Methods verbs

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• Objects are a particular instance of a class
• A class is like a blueprint for making objects
• Objects have methods
• The main method is often present, as on page 27
• Objects may contain data

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Three Design Principles

• Encapsulation aka information hiding
• Polymorphism
• Inheritance
• Ill do this second

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Encapsulation

• An object has
• the right, the ability, the obligation (?)
• to hide what is inside itself data and methods
  from the rest of the world. Why??
• Control security safety
• also flexibility

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Flexibility ?

• If the outside world cant see how the object
  works,it cant become aware of and then utilize
  that knowledge in ways that make it dependent on
  the implementation in the object. Because of
  this flexibility I can change the implementation
  way the object does things without a care that
  it will hurt those who use the object

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Inheritance

• A class, and the objects instantiated from that
  class, can either be done from scratch you would
  have assumed that or !!! thats emphasis they
  can be built upon a previously written class.
• extended from and inherit from are synonyms
  for built upon

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• That means if I have a soldier class, I can
  extend it by writing a enlisted class and an
  officer class. The officer class can be extended
  to the various ranks and the same for the
  enlisted class. Each derived class will be based
  upon its super class. The particulars of the
  Lieutenant class will be written to either add to
  the basic class for an officer in case theres
  something that Lieutenants do that other officers
  dont or

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• Rewritten to reflect the ways in which a
  Lieutenant does the same thing but in a different
  manner.

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Polymorphism

• Lets imagine that all officers get some
  allowance for uniforms. It depends on their rank
  and years of service.
• One could write a shared method for doing it.
  It would contain selection logic.
• The problem is that the creation of a new rank
  would require going into the officer

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• class and modifying the selection logic. With
  inheritance, each class such as Lieutenant
  would have its own much simpler version of the
  calculation of the allowance for uniform
• The creation of a new rank would necessitate the
  creation of a new class inherited from the
  officer class.
• So!! Wheres the polymorphism?

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• The polymorphism comes in because I can invoke
  the calculate allowance for uniforms method
  without needing to know whether the object Im
  dealing with is a Lieutenant or a Captain or some
  other, perhaps new, rank.
• It simplifies my coding that use officer
• It simplifies maintenance

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1.4 A Taste of Java

• Applets later both in Ch. 1 and much later
• Java application
• Spelling rules
• Compiling and Running

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Applets

• An applet is a java program that runs in a
  browser on the client side thats the user side
  its not the server side
• We will look at Display 1.6 and 1.7 on pages 38
  39, later

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Java Application

• See page 27, Display 1.5

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Spelling Rules

• Java is case sensitive
• VB is case insensitive
• There are standards for when to capitalize
• We will cover them later
• There are keywords

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Compiling and Running

• These are more distinct activities than they were
  in VB
• To compile without TextPad
• or you can look at it as being what TextPad does
• javac TheClass.java
• This takes a .java file and makes a .class file
• To run
• java TheClass