Alexander Shvets - Design Patterns Explained Simply

This book isn't an introduction to object-oriented technology or design. Many books already do a good job of that. This isn't an advanced treatise either. It's a book of design patterns that describe simple and elegant solutions to specific problems in object-oriented software design.

Once you understand the design patterns and have had an "Aha!" (and not just a "Huh?" experience with them, you won't ever think about object-oriented design in the same way. You'll have insights that can make your own designs more flexible, modular, reusable, and understandable - which is why you're interested in object-oriented technology in the first place, right?

Design patterns can speed up the development process by providing tested, proven development paradigms. Effective software design requires considering issues that may not become visible until later in the implementation. Reusing design patterns helps to prevent subtle issues that can cause major problems and improves code readability for coders and architects familiar with the patterns.

Often, people only understand how to apply certain software design techniques to certain problems. These techniques are difficult to apply to a broader range of problems. Design patterns provide general solutions, documented in a format that doesn't require specifics tied to a particular problem.

In addition, patterns allow developers to communicate using well-known, well understood names for software interactions. Common design patterns can be improved over time, making them more robust than ad-hoc designs.

This design patterns is all about class instantiation. This pattern can be further divided into class-creation patterns and object-creational patterns. While class-creation patterns use inheritance effectively in the instantiation process, object-creation patterns use delegation effectively to get the job done.

• 
  Creates an instance of several families of classes
• 
  Separates object construction from its representation
• 
  Creates an instance of several derived classes
• 
  Avoid expensive acquisition and release of resources by recycling objects that are no longer in use
• 
  A fully initialized instance to be copied or cloned
• 
  A class of which only a single instance can exist

This design patterns is all about Class and Object composition. Structural class-creation patterns use inheritance to compose interfaces. Structural object-patterns define ways to compose objects to obtain new functionality.

• 
  Match interfaces of different classes
• 
  Separates an objects interface from its implementation
• 
  A tree structure of simple and composite objects
• 
  Add responsibilities to objects dynamically
• 
  A single class that represents an entire subsystem
• 
  A fine-grained instance used for efficient sharing
• 
  Restricts accessor/mutator access
• 
  An object representing another object

This design patterns is all about Class's objects communication. Behavioral patterns are those patterns that are most specifically concerned with communication between objects.

• 
  A way of passing a request between a chain of objects
• 
  Encapsulate a command request as an object
• 
  A way to include language elements in a program
• 
  Sequentially access the elements of a collection
• 
  Defines simplified communication between classes
• 
  Capture and restore an object's internal state
• 
  Designed to act as a default value of an object
• 
  A way of notifying change to a number of classes
• 
  Alter an object's behavior when its state changes
• 
  Encapsulates an algorithm inside a class
• 
  Defer the exact steps of an algorithm to a subclass
• 
  Defines a new operation to a class without change