Object Oriented Programming in Java 95707

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Object Oriented Programming in Java

• Object Oriented Concepts

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What is an Object?

• An object is a software bundle of related
  variables and methods.
• Software objects are often used to model
  real-world objects you find in everyday life

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State and Behavior

• The State of an object is represented by the
  values of its variables
• The Behavior of an object is represented by its
  methods

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Encapsulation

• Not a new idea. Examples are
• DLLs in Windows
• Procedure in Pascal
• Functions in C
• Important because of the need to
• keep system modular
• promote information hiding

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Controlling Access to Objects State and Behaviors

• Java has a number of built-in mechanism to do so
  using simple keywords such as
• private
• public
• protected

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What is a Message

• Software objects communicate between each other
  by sending messages to each other.

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Parts of a Message

• Destination
• object name
• Name of behavior to exercise
• object method
• How to modify behavior and state
• parameters

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Why are messages so great?

• Allows hiding of internal data structures
• Allows hiding on internal process logic
• Allows remote calls

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What is a Class?

• A class is a blueprint or prototype that defines
  the variables and methods common to all objects
  of a certain kind
• Different objects can have the same class
• Cars, Vans, Trucks are all objects of the class
  automobile
• Are automobiles different from vehicles?

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Differences between Object and Classes

• Source of confusion because of several
  definitions
• In general
• Objects are instances of their respective class

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What are the possible relationships between
objects

• Is-a relationship
• implements the behavior of some type
• Inheritance relationship
• subclass of some other object
• Is made of relationship
• declares other objects

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Inheritance

• Key concept in OO programming
• Very powerful
• To be used very carefully
• Java enforces a single inheritance model
• can inherit State and Behavior from super class
• can override or add to super class state and
  behavior

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Interfaces

• Very powerful
• Difficult to understand where to use at first
• To be used a lot
• Allows to
• capture similarities between classes without
  artificially forcing a relationship

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Modeling Example

• Write an OO program that simulates a furnace, a
  thermostat, and a user.
• Example behaviors and states
• First the thermostat gets the set point from the
  user. Then the thermostat get the current
  temperature from a thermometer.
• Then the thermostat tests the current temperature
  against the set point. If the current
  temperature is above the set point, the
  thermostat does not to turn the furnace on (or
  turns it off if already on)
• When the furnace is turned on it announces that
  it has been turned on.