Design pattern git repo got 100 forks ;-)

Proud Moment. I got 100 forks on my Github repository for the code base of  “Design Patterns” 

Here is the link – https://github.com/premaseem 

It gives a lot of satisfaction when you realize that code written by you is liked and used by several other developers in this world. 

My Book on design patterns is now available on Udemy platform

Friends,

It was my deep down wish to be an instructor on Udemy platform and with Guru’s grace it got fulfilled today.

My video Book on “Learn software design patterns with Java” is now available on Udemy as on line course. Students would also get the certificate of completion once they finish the entire course.

https://www.udemy.com/learn-design-patterns-with-java/

 

 

Architecture: Bridge Design Pattern

Hi Friends,
I have made a project of “Remote Control Application” by implementing Bridge design pattern.

Project: Solves the problem of dependency / coupling between parallel development / evolution of 2 different components by creating a bridge between their interfaces 😉

What is Bridge Design Pattern: decouples an abstraction so two classes can vary independently

Github project code: https://github.com/premaseem/DesignPatternsJava9/tree/bridge-pattern

I have written the working code based on the Architectural diagram, which can be downloaded from Github.

Architecture: Facade design pattern

Hi Friends,
I have made a project of  “All in one remote controller”  by implementing Facade design pattern.

Project: Solves the problem of too many TV / entertainment unit remotes by using a simplified master remote control ( which acts as Facade here )

What is Facade Design Pattern: provides a simple interface to a more complex underlying object.

Github project code: https://github.com/premaseem/DesignPatternsJava9/tree/facade-pattern

I have written the working code based on the Architectural diagram, which can be downloaded from Github.

 

 

 

Architecture: Adapter design pattern

Adapter Design Pattern allows for two incompatible classes to work together by wrapping an interface around one of the existing classes

I have written the working code based on the Architectural diagram, which can be downloaded from Github.

Working code github link: https://github.com/premaseem/DesignPatternsJava9/tree/adapter-pattern

 

 

Architecture: Proxy design pattern

I have written the working code based on the Architectural diagram, which can be downloaded from Github

Working code github link:  https://github.com/premaseem/DesignPatternsJava9/tree/proxy-pattern

 

 

 

Good Design vs Bad Design – Information overload

The Bad: Parking Signs in Los Angeles

Parking signs in Los Angeles (LA) have been the epitome of information overload for decades. They’ve always been notoriously hard to understand, because the traffic rules are complex, resulting in the need to convey a lot of information in a small area.

How confusing are these signs? Traditionally, very—look at this example from the 2010s:

Author/Copyright holder: Jorge Gonzalez. Copyright terms and licence: CC BY-SA 2.0

As LA parking signs go, this example is already a pretty simple one.

Imagine you are a driver along this road on a Tuesday morning at 9 a.m. Can you park at this spot? What sounds like a simple question takes a lot of mental processing to answer.

As designers, we’re often faced with situations where we have to design for a lot of information to be displayed in a small space. The parking signs in LA might be an extreme case, but many times designing for mobile apps means facing the same problems. Is there a way out—for both the parking signs and designers in general?

The Good: Nikki Sylianteng’s Parking Sign

Designing a sign to display all the information, while being easy to understand, sounds like an impossible task. But that’s exactly what Brooklyn designer Nikki Sylianteng did.

Author/Copyright holder: Nikki Sylianteng. Copyright terms and licence: CC BY-NC-SA 4.0

Nikki’s proposed parking sign was eventually used in LA as part of a trial run.

Part of why Nikki’s design¹ works well is that it is user-centred: Nikki realised drivers simply want to know whether they can park at a spot. Yes or no—that’s all drivers needed, and that’s all the parking sign shows.

Her design also made use of visuals, rather than text, to convey information. The result is incredibly intuitive: green for OK, red for No Parking. It’s even designed for the colour blind, with stripes for No Parking.

Now when you look at the sign, you’ll know that on Tuesday at 9 a.m., parking is not allowed. The bars show what’s what at a glance—simple.

Lessons Learnt: Best Practice

• Understand what your users need, then design based on that. This helps reduce information overload.
• Have lots of information to convey to your users? Try using visuals instead of text. Learn more about data visualisation here.

Software Development AntiPatterns

Good software structure is essential for system extension and maintenance. Software development is a chaotic activity, therefore the implemented structure of systems tends to stray from the planned structure as determined by architecture, analysis, and design.

Software refactoring is an effective approach for improving software structure.

The resulting structure does not have to resemble the original planned structure.

The structure changes because programmers learn constraints and approaches that alter the context of the coded solutions. When used properly, refactoring is a natural activity in the programming process.

For example, the solution for the Spaghetti Code AntiPattern defines a software development process that incorporates refactoring. Refactoring is strongly recommended prior to performance optimization. Optimizations often involve compromises to program structure. Ideally, optimizations affect only small portions of a program. Prior refactoring helps partition optimized code from the majority of the software.

Development AntiPatterns utilize various formal and informal refactoring approaches. The following summaries provide an overview of the Development AntiPatterns found in this chapter and focus on the development AntiPattern problem. Included are descriptions of both development and mini-AntiPatterns. The refactored solutions appear in the appropriate AntiPattern templates that follow the summaries.

• The Blob
  Procedural-style design leads to one object with a lion’s share of the responsibilities, while most other objects only hold data or execute simple processes. The solution includes refactoring the design to distribute responsibilities more uniformly and isolating the effect of changes.
• Continuous Obsolescence
  Technology is changing so rapidly that developers often have trouble keeping up with current versions of software and finding combinations of product releases that work together. Given that every commercial product line evolves through new releases, the situation is becoming more difficult for developers to cope with. Finding compatible releases of products that successfully interoperate is even harder.
• Lava Flow
  Dead code and forgotten design information is frozen in an ever-changing design. This is analogous to a Lava Flow with hardening globules of rocky material. The refactored solution includes a configuration management process that eliminates dead code and evolves or refactors design toward increasing quality.
• Ambiguous Viewpoint
  Object-oriented analysis and design (OOA&D) models are often presented without clarifying the viewpoint represented by the model. By default, OOA&D models denote an implementation viewpoint that is potentially the least useful. Mixed viewpoints don’t allow the fundamental separation of interfaces from implementation details, which is one of the primary benefits of the object-oriented paradigm.
• Functional Decomposition
  This AntiPattern is the output of experienced, nonobject-oriented developers who design and implement an application in an object-oriented language. The resulting code resembles a structural language (Pascal, FORTRAN) in class structure. It can be incredibly complex as smart procedural developers devise very “clever” ways to replicate their time-tested methods in an object-oriented architecture.
• Poltergeists
  Poltergeists are classes with very limited roles and effective life cycles. They often start processes for other objects. The refactored solution includes a reallocation of responsibilities to longer-lived objects that eliminate the Poltergeists.
• Boat Anchor
  A Boat Anchor is a piece of software or hardware that serves no useful purpose on the current project. Often, the Boat Anchor is a costly acquisition, which makes the purchase even more ironic.
• Golden Hammer
  A Golden Hammer is a familiar technology or concept applied obsessively to many software problems. The solution involves expanding the knowledge of developers through education, training, and book study groups to expose developers to alternative technologies and approaches.
• Dead End
  A Dead End is reached by modifying a reusable component if the modified component is no longer maintained and supported by the supplier. When these modifications are made, the support burden transfers to the application system developers and maintainers. Improvements in the reusable component are not easily integrated, and support problems can be blamed upon the modification.
• Spaghetti Code
  Ad hoc software structure makes it difficult to extend and optimize code. Frequent code refactoring can improve software structure, support software maintenance, and enable iterative development.
• Input Kludge
  Software that fails straightforward behavioral tests may be an example of an input kludge, which occurs when ad hoc algorithms are employed for handling program input.
• Walking through a Minefield
  Using today’s software technology is analogous to walking through a high-tech mine field. Numerous bugs are found in released software products; in fact, experts estimate that original source code contains two to five bugs per line of code.
• Cut-and-Paste Programming
  Code reused by copying source statements leads to significant maintenance problems. Alternative forms of reuse, including black-box reuse, reduce maintenance issues by having common source code, testing, and documentation.
• Mushroom Management
  In some architecture and management circles, there is an explicit policy to keep system developers isolated from the system’s end users. Requirements are passed second-hand through intermediaries, including architects, managers, or requirements analysts.

Interpreter Design Pattern

Download the working example demo code in java from my GIT repository –
https://github.com/premaseem/designPatterns/tree/master/ZipDownloadableProjects

Example Code Description :
1. Date interpreter example : The main cause of Y2K virus was interpretaiton of date format, in this example code I tried to address the same so that system can intrepret any date given in any formats. we have a interpreter for DD, MM and YYYY (rule to pick the date from context) so you provide the format and system gives you the conversion. Straight forward. 
2. And Or Expression : This example taks a string where in it should match the expression based on rule which accomplies And / Or expression. Code is simple and small but a bit triky to get hold of. Feel free to downlaod and play with it.

Direct link :
https://drive.google.com/file/d/0B-9WtmpPhI4ZREEwNWpRYWVzSGM/view?usp=sharing

Intent

• Given a language, define a representation for its grammar along with an interpreter that uses the representation to interpret sentences in the language.
• Map a domain to a language, the language to a grammar, and the grammar to a hierarchical object-oriented design.

Problem Area

This interpreter design pattern does not give solution for building a whole large interpreter for a language. It can be applicable for smaller chunks where grammar and interpretation is applicable. We can consider scenarios like regular expressions and interpreting mathematical expression.

Discussion

The Interpreter pattern discusses: defining a domain language (i.e. problem characterization) as a simple language grammar, representing domain rules as language sentences, and interpreting these sentences to solve the problem. The pattern uses a class to represent each grammar rule. And since grammars are usually hierarchical in structure, an inheritance hierarchy of rule classes maps nicely.

 

An abstract base class specifies the method interpret(). Each concrete subclass implements interpret() by accepting (as an argument) the current state of the language stream, and adding its contribution to the problem solving process.

Example

The Intepreter pattern defines a grammatical representation for a language and an interpreter to interpret the grammar. Musicians are examples of Interpreters. The pitch of a sound and its duration can be represented in musical notation on a staff. This notation provides the language of music. Musicians playing the music from the score are able to reproduce the original pitch and duration of each sound represented.

Check list

1. Decide if a “little language” offers a justifiable return on investment.
2. Define a grammar for the language.
3. Map each production in the grammar to a class.
4. Organize the suite of classes into the structure of the Composite pattern.
5. Define an interpret(Context) method in the Composite hierarchy.
6. The Context object encapsulates the current state of the input and output as the former is parsed and the latter is accumulated. It is manipulated by each grammar class as the “interpreting” process transforms the input into the output.

Memento Design Pattern

Download the working example demo code in java from my GIT repository –
https://github.com/premaseem/designPatterns/tree/master/ZipDownloadableProjects

Example Code Description :
1. Video Game Example : You can pick your player name, its mask and other details. You earn few more points and get the option to save the games state. Later you can restore your games state as well. The memento is used basically which clones your domain object and keeps it with itself. Care taker is the class which interects with client and talks to Originator. Originator component detals with domain object to save and restore the momento. Download, run and enjoy the game 🙂

Direct link :
https://drive.google.com/file/d/0B-9WtmpPhI4ZLV9rcFlmOXN2N0U/view?usp=sharing

Intent

• Without violating encapsulation, capture and externalize an object’s internal state so that the object can be returned to this state later.
• A magic cookie that encapsulates a “check point” capability.
• Promote undo or rollback to full object status.

Problem

Need to restore an object back to its previous state (e.g. “undo” or “rollback” operations).

Discussion

The client requests a Memento from the source object when it needs to checkpoint the source object’s state. The source object initializes the Memento with a characterization of its state. The client is the “care-taker” of the Memento, but only the source object can store and retrieve information from the Memento (the Memento is “opaque” to the client and all other objects). If the client subsequently needs to “rollback” the source object’s state, it hands the Memento back to the source object for reinstatement.

An unlimited “undo” and “redo” capability can be readily implemented with a stack of Command objects and a stack of Memento objects.

 

The Memento design pattern defines three distinct roles:

1. Originator – the object that knows how to save itself.
2. Caretaker – the object that knows why and when the Originator needs to save and restore itself.
3. Memento – the lock box that is written and read by the Originator, and shepherded by the Caretaker.

Check list

1. Identify the roles of “caretaker” and “originator”.
2. Create a Memento class and declare the originator a friend.
3. Caretaker knows when to “check point” the originator.
4. Originator creates a Memento and copies its state to that Memento.
5. Caretaker holds on to (but cannot peek into) the Memento.
6. Caretaker knows when to “roll back” the originator.
7. Originator reinstates itself using the saved state in the Memento.

Rules of thumb

• Command and Memento act as magic tokens to be passed around and invoked at a later time. In Command, the token represents a request; in Memento, it represents the internal state of an object at a particular time. Polymorphism is important to Command, but not to Memento because its interface is so narrow that a memento can only be passed as a value.
• Command can use Memento to maintain the state required for an undo operation.
• Memento is often used in conjunction with Iterator. An Iterator can use a Memento to capture the state of an iteration. The Iterator stores the Memento internally.