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• Inheritance


  Allows a class to reuse the code from another class without duplicating it
• Inheritance


  • Parent class has properties and methods, child class can use the code from the parent class
  • Allows you to write the code in the parent class and use it in both parent and child classes
• Parent class


  Also called a base class or super class
• Child class


  Also known as a derived class or a subclass
• Defining a class that inherits from another class

  Use the extends keyword
• Interface


  Establishes a contract that a class must adhere to, a blueprint for classes
• Interfaces


  • Specify what methods a class should implement
  • Declared with the interface keyword
  • Consist of methods with no implementations, all methods must have public visibility
  • Classes can implement one or more interfaces
  • Classes must implement all the methods defined in an interface
  • Can be extended using the extends operator
  • Can contain methods and/or constants, but no attributes

  
• The class which implements an interface is called the Concrete Class
• Interfaces allow you to specify what methods a class should implement
• Interfaces are different from classes as the class can inherit from one class only whereas the class can implement one or more interfaces
• Interfaces can be extended to another interface
• A class implements an interface using the implements operator
• Design patterns


  Typical solutions to commonly occurring problems in software design, pre-made blueprints that can be customized
• Patterns vs Algorithms


  Algorithm defines a clear set of actions to achieve a goal, pattern is a high-level description of a solution
• Patterns were first described by Christopher Alexander in A Pattern Language: Towns, Buildings, Construction
• The concept of design patterns was applied to programming by Erich Gamma, John Vlissides, Ralph Johnson, and Richard Helm in their 1994 book Design Patterns: Elements of Reusable Object-Oriented Software
• Most programmers work for many years without knowing about a single pattern, they might be even implementing some patterns without knowing it
• Why learn design patterns

  • They are a toolkit of tried and tested solutions to common problems in software design, teach principles of object-oriented design, provide a common language for communication
• Criticism of design patterns

  • Kludges for a weak programming language
  • Inefficient solutions
  • Unjustified use
• Classification of design patterns

  • Idioms are basic, low-level patterns that apply to a single programming language
  • Architectural patterns are the most universal, high-level patterns that can be used to design the architecture of an entire application
• Types of design patterns by intent

  • Creational patterns
  • Structural patterns
  • Behavioral patterns