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Object Oriented Programs: Basic Concepts

Object Oriented Programs: Basic Concepts. Nick West. Drawbacks of “Structured” Design. Working in Solution Domain Process Dominated But Program = Software and Data! Data structuring takes second place . Reusability Not Encouraged

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Object Oriented Programs: Basic Concepts

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  1. Object Oriented Programs:Basic Concepts Nick West

  2. Drawbacks of “Structured” Design • Working in Solution Domain • Process Dominated • ButProgram = Software and Data! • Data structuring takes second place. • Reusability Not Encouraged • But“The best way not to create bugs is not to write code!” Process • This is a Computer, but more natural to describe problem in terms of Objects

  3. The World is Full of Objects! • Consider:- • Power Supply:- • Just a source of 240V AC. • Not a complex of circuits, grids, transformers, power stations… • Telephone:- • Just connects to a remote phone. • Not a complex of circuits, exchanges, land lines, satellite links… • Simple Model (Data Abstraction) • Hidden Complexity (Data Hiding). • PC Hardware • Bus • Memory • CPU • Screen • Disk Drive Could this be done in Software? } All have Internal Complexity. But relatively simple Interface. Allows - Upgrading existing PC - Building new PC.

  4. Object Oriented Paradigm • Object: • A miniture Program consisting of:- • Set of internal variables. • Set of functions to manipulate them. • Externally:- • Only access functions. • Variables hidden; object controls access. • Immediate Advantages • More Natural - to state problem in terms of objects. Also good for User Interface. • Data Hiding • As with SA/SD only specify function; implementation can change. • Unlike SA/SD data can change, leads naturally to data abstraction. • Locality or Data Encapsulation ensures code robust; can rigorously test all states and flow paths.

  5. Classes and Inheritance • CLASSES Sets of objects with similar properties form a class. Can create an arbitrary number of objects (called instances of class). • INHERITANCE Can create a new class (subclass) developed from another (base class) by adding more variables and functions. Example: Window Manager Event Display Spreadsheet Editor Subclass (application specific) Base class (for basics e.g. move, resize, iconise) Window

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