Computer Science II 810:062 Section 01

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Computer Science II810062 Section 01
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How is CS I different from CS II?

• When you teach Java there are a series of
  decisions that have to be made

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How is CS I different from CS II?

• When you teach Java there are a series of
  decisions that have to be made
• Applet or Applications
• Core Java or Textbook package
• IDE or command line
• Object Oriented or structured
• Event-driven or Non-event driven

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How is CS I different from CS II?

• When you teach Java there are a series of
  decisions that have to be made
• Applet or Applications
• Core Java or Textbook package
• IDE or command line
• Object Oriented or structured
• Event-driven or Non-event driven

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How is CS I different from CS II?

• When you teach Java there are a series of
  decisions that have to be made
• Applet or Applications
• Core Java or Textbook package
• IDE or command line
• Object Oriented or structured
• Event-driven or Non-event driven

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How is CS I different from CS II?

• CS I focuses on learning to program in the first
  place.
• CS II focuses on learning how to program well
  using the paradigm of Object Oriented
  Programming.

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So what is OO programming?

• Object-oriented programming changes the way
  software developers think about the problem by
  redefining the problem.
• Object-oriented programming encourages us to
  think about the computer as a simulator of the
  world. Thus, a program is a map of the world we
  want to imitate.

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So what is OO programming?

• Instead of asking
• How can I write a program that is structured like
  the machine on which it runs?
• We ask
• How can I write a program that is structured like
  the part of the world it describes?

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So what is OO programming?
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The anatomy of an OO program

• The world
• consists of objects
• that interact
• to solve a problem.

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So what is OO programming?

• In Java, the main thing you do is write class
  definitions. (R. Morelli)
• A class definition encapsulates two (three
  actually) things
• Data (instance variables)
• Actions (constructors and methods).

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So what is OO programming?

• But a class on its own is nearly worthless.
• The purpose of a class is to serve as a template
  for creating individual objects, or instances, of
  the class.

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The anatomy of an OO program

• An object is an instance of a class
• MemoPad p new MemoPad()
• While a class describes a set of objects that
  behave similarly, each instance of a class is
  distinct and has its own state.
• MemoPad p new MemoPad()
• MemoPad q new MemoPad()

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So what is OO programming?

• an object-oriented program is a set of objects
  that collaborate to achieve a goal
• objects interact by sending each other messages
  (invoking an objects method).

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Lets consider a MemoPad example
Allows for the storage of a collection of memos
that are associated with keys
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For example, you can insert an memo
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Identify the objects needed in the MemoPadApp
example
List the objects and their behaviors
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What came first the chicken or the egg?Since
objects create other objects dynamically as
needed, where does the first object come from?
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The anatomy of an OO program

• The world is a class that contains the main()
  function.
• main() is the big bang that creates one or more
  objects.
• public class MemoPadApp
• public static void main( String args )
  MemoPad p new MemoPad()
  p.show() // end main
• // end class MemoPadApp

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So what is OO programming?

• Notice that main is a static method.
• We will discuss what static means in more detail
  later this semester, but for now you can think of
  this modifier as saying that main is associated
  with the class memoPadApp, and not with any
  instance of the class.
• main is a class method.

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So what is OO programming?

• an object-oriented program is a set of objects
  that collaborate to achieve a goal
• objects interact by sending each other messages
  (invoking an objects method).

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So how do objects collaborate?

• They send one another messages.
• In response to a message, an object executes the
  method associated with the message that it
  receives, both names and arguments.
• A big part of designing an object-oriented system
  is deciding what messages each object should
  respond to.
• The set of messages to which an object responds
  is called its interface.

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Designed an interface for the memo database class

• the memo database class is used to hold the
  actual memos being stored
• its interface is the set of messages to which it
  should respond

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Think about

• What is the behavior of a memo database?
• What should it do in order to contribute to the
  world of objects that implements the behavior of
  a memo pad?

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Interface for the memo database

• public interface MemoDatabase
• // end interface MemoDatabase

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Interface for the memo database

• public interface MemoDatabase
• public String find ( String key )
• // end interface MemoDatabase

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Interface for the memo database

• public interface MemoDatabase
• public String find ( String key )
• public boolean remove ( String key )
• public boolean insert (MemoAssociation m)
• public boolean containsKey( String key )
• // end interface MemoDatabase

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For next class

• Read chapter 1. Identify any concepts or terms
  that are new to you so we can discuss them.
• Re-acquaint yourself with the Java tools
  available at home or in the lab. Download the
  MemoPad code from the course Java page, and play
  with it.