Understanding OOP

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Understanding OOP

• Java and Object-Oriented Programming

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Lecture Goals

• Understand how Java is both compiled and
  interpreted
• Understand the history of OOP
• Understand the term object
• Understand the concept of class
• Understand the concept of instance
• Understand the concept of a reference

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In the Beginning

• Programming was done by re-wiring hundreds of
  thousands of wires
• Extremely tedious
• Extremely error-prone

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Machine Language

• Instructions stored as data
• Still binary, though
• Tied to specific CPUs
• Tedious
• Difficult to write
• Difficult for humans to understand

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Higher-Level Languages
Java

• Allowed humans to work in a more human-like
  language
• Could be translated to machine language

C
Python
Visual Basic
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Interpreted vs. Compiled
Higher Level Languages can either be Interpreted
or Compiled

• Interpreted
• Similar to a real-time English translator
• Very slow
• Very flexible
• Examples
• Perl
• JavaScript
• Logo

• Compiled
• Entire program is translated first
• Much faster
• Some flexibility is lost
• Examples
• C
• C

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Evolution of Languages
Linear Languages

• Things are done one at a time
• No human intervention
• Sequential logic
• Entire program is a single entity
• Spaghetti code
• Example BASIC

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Evolution of Languages
Procedural Languages

• Programs are broken into procedures
• Structured Programming
• Each procedure is broken into a self-contained
  program
• Parameter Passing
• Examples Pascal, C

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Evolution of Languages
Object Oriented Languages

• Descendent of procedural languages
• Programs and data are objects (an object is a set
  of data and the procedures to manipulate that
  data)
• Event-driven interface
• Example Java

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How does Java fit?

• Java is heavily object oriented
• Java is event-driven (user controls outcome)
• Java can be used as a full-fledged programming
  environment
• Java is integrated very well into the Web
• Java is somewhat platform-independent
• Java is both compiled and interpreted

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Compiled and Interpreted!
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Programming as Modeling

• Model elements represent more complex things
• Model elements exhibit consistent behavior
• Different elements can be grouped into different
  categories based on common behaviors
• Actions external to the model can cause the
  behavior of an element

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Objects in Java

• Model elements in Java are called objects
• Objects can exhibit behavior based on reactions
  to environment
• Objects with similar behavior can be grouped into
  categories called classes
• Every object belongs to one class and is said to
  be an instance of that class
• Instances inherit all the properties and
  behaviors of their parent class
• In programs, we use references as phrases which
  refer to an object

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Questions?