1.4 Principles of Programming

• High Level Languages


  Programming languages closer to English and use recognisable words
• Low Level Languages


  Programming languages closer to the internal workings of a computer - could be binary or other short codes
• Assembly language


  • A step above machine code
• High Level Languages- Benefits


  • Easier to understand, learn and program as commands are more English-like
  • Identifiers can be long and meaningful
  • Allow the use of powerful commands that perform quite complex tasks
  • Allow creation of modules that can be re-used and accessed by other parts of the program
• Low Level Languages- Benefits


  • Ideal when the execution speed is critical, e.g. boot strap loader
  • More efficient than high level language programs
  • Require less time for translation into machine code
  • Generally result in smaller executable programs
• Applications requiring low level languages


  • Device Drivers
  • Embedded software
  • Interfacing with custom hardware
• Procedural Languages


  • Used in traditional programming based on algorithms or a logical step-by-step process for solving a problem
  • Obey ordered instructions
  • Carry out actions / calculations
• Procedural Languages


  • Provide the programmer a way to define precisely each step when performing a task
  • Allow tight control over the underlying operation of the hardware
  • Used in large complicated programs where similar operations may be carried out at varying stages of the program execution
• Non-Procedural Languages


  • Allow programmers to specify the results they want without specifying how to solve the problem
  • Used in database interrogation where retrieving answers are more important than the exact steps required to calculate the result
  • Used in Artificial intelligence, grammar checking and language translation applications
• Object Oriented Language / Programming (OOL/OOP)


  • Uses objects - include both data and associated processing
  • Enables production of buttons / icons, etc - useful in a visual environment
  • Uses features such as inheritance, encapsulation
• OOP - Advantages

  • Improved productivity when developing software due to the flexible and extendable nature of OOP
  • Software is easier to maintain as OOP is modular and reusable
  • Development is faster due the reusable code and libraries
  • Development is cheaper
  • Software can be tested more easily making it more high quality
  • Software is easier to design as model the real world
• OOP - Disadvantages


  • OOP is difficult and not as 'logical' to some developers, it is complex to create application in
  • Software can become larger - more code - than procedural programs
  • OOP programs can run slower than PP as there is more code to execute
  • OOP cannot be used for all types of software application such as machine learning and AI
  • OOP can be difficult to debug
• Class


  A template or blueprint for a specific object. It defines an object's instance variables (attributes/properties) and behaviour (methods)
• Object


  An instance of a class
• Method


  A programmed behaviour/subroutine that is included in an object of a class. A method can only access data within its own object (encapsulation)
• Inheritance


  • Enables new objects to take on the properties of existing objects
  • A superclass is used as the basis for inheritance. A class that inherits from a superclass is called a subclass
  • Defines relationships between classes and organises classes into groups
  • Enables classes that are similar to existing classes to be created by indicating differences (rather than starting again) and therefore allows code to be organised and re-used effectively
• Abstraction


  The process of hiding non-essential features and showing the essential features
• Encapsulation


  • The hiding of the implementation of a class and controlling access to its methods and attributes
  • Classes can hide how they work from developers who may wish to use them in their programs
  • Anyone using the class needs only to understand the interface - i.e: its methods and attributes
• Polymorphism


  The characteristic of being able to assign a different meaning or usage to something in different contexts - specifically, to allow an entity such as a variable, a function, or an object to have more than one form
• Object Hierarchy


  • It references descendants of objects acting as properties of an object
  • An example of this would be the object controlling a window (at the top of the hierarchy) having another object like the window's border acting as a property of the window
• Event Driven Language


  • Used in situations that rely on Events
  • Events could be triggered by input devices (on mouse click) or by external sensors (e.g: pressure)
• Visual Language


  • Particularly suitable for production of objects / buttons / icons, etc
  • Particularly suitable for developing in a GUI/Windows/graphics content/event driven environment
  • May be easier to learn / more intuitive because they are visual - there is very good help / tools available
• Mark-up Languages


  • Use tags to specify the format of data
  • E.g: HTML - Hypertext Markup Language
  • Can easily be written in any basic text editor
  • The tags are interpreted by the browser when the page is displayed
• It is important that there are agreed standards in programming languages, even across different manufacturers
• This would allow commands from Borland C++ to work in Microsoft C++
• Ambiguity in natural language


  • Means that a statement can be interpreted in more than one way
  • This is difficult enough in English but makes it impossible for a computer to interpret
  • When defining programming languages it is essential that no ambiguity exists