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The Pattern Language is an organized and coherent set of patterns, each of which describes a problem and the core of a solution that can be used in many ways within a specific field of expertise.

In the last chapter, you saw waits and timeouts. Protractor can be used with different types of frameworks. Choosing a framework depends on a lot of different factors. Protractor’s flexibility allows it to be implemented using any of the frameworks on the market. This chapter looks at the following, including frameworks that are compatible with Protractor.

Although design patterns simply describe solutions to problems, they tend to emphasize solutions that promote reusability and flexibility. To achieve this, they manifest some key object-oriented design principles. We will encounter some of them in this chapter and in more detail throughout the rest of the book.

With strategies for generating objects covered, we’re free now to look at some strategies for structuring classes and objects. I will focus in particular on the principle that composition provides greater flexibility than inheritance. The patterns I examine in this chapter are once again drawn from the Gang of Four catalog.

When we deal with architecture and design, we immediately start thinking about recipes and patterns. These design patterns are useful for building reliable, scalable, secure applications in the cloud.

In the previous chapter, we talked about security, adding authentication and authorization to our Daniel's Delivery website, from the back end to the front end. We know that building quality software is not an easy task. There are plenty of frameworks and practices that we should take into account to transform business requirements into software systems. Best practices and design patterns are two of the main topics we should add to any system to improve its quality.

Welcome to Chapter 3, the developer chapter. Thank you for following along the first two chapters, where the book explained the required steps to start a custom SAP Fiori application starting from the design phase and then analyzing and playing with data or even simulating it when data is not available. This chapter focuses on the actual implementation of an SAP Fiori application and primarily focuses on the developer. In this chapter, the book dives deeper into the different areas that make up a Fiori application; it explains the software design pattern known as MVC (Model-View-Controller) and the different tools for developing and debugging such as the SAP Web IDE. It also talks about integrating third-party JavaScript libraries into our SAP Fiori web application, and then it shows various scenarios as to how the Fiori application is seen from different devices such as desktops, tablets, and phone devices.

MVC is a software design pattern. It describes the separation of software into three elements

Design patterns let you benefit from other people’s experiences, which is often called experience reuse. You learn how they solved challenges, how they tried to adopt new behaviors in their systems, and so on. A pattern may not perfectly fit into your work, but if you concentrate on the best practices as well as the problems of a pattern at the beginning, you are more likely to make a better application. This is why I will now discuss design pattern criticisms. Knowing about them can offer you some real value. If you think critically about patterns before you design your software, you can predict your return on investment to some degree. Let’s go through the following points that are often raised by some developers

Building upon the last chapter, in this chapter we will start architecting the game engine. For each chapter, we will implement another component until completion. Proper planning and architecting are crucial to creating a successful engine, game (or any program for that matter). This chapter will also go over a couple design patterns used in game engines in case you want to explore other patterns in your own projects.

Software architectures are comparatively easy to comprehend, especially if there is enough documentation on the subject. The hardship will emerge when you start implementing them to solve real-world problems. This is where architectural patterns will come to your rescue. If you understand the problem at hand and if you can reasonably attach this problem to a scenario similar to a problem you have already addressed, it’s rather easy to follow an approach similar to what you adopted earlier. Architecture and design patterns help you to choose and adopt solutions to problems that are similar in nature. A pattern is a reusable solution to repetitive problems of a similar nature that occur in a particular context.

The discussion of design patterns cannot be completed without antipatterns. This chapter briefly overviews antipatterns. Let’s start.

After discussing API design patterns, I would like to dedicate a complete chapter to this topic due to its importance. All APIs need to know who they are being used by. The answer is provided via authentication and authorization mechanisms. Whatever gets implemented, always remember this

Good craftspeople can draw on a wealth of experience and knowledge. Once they’ve found a good solution for a certain problem, they take this solution into their repertoire to apply it in the future to a similar problem. Ideally, they transform their solution into something that is known as a canonical form and document it, both for themselves and for others.

The next stop on our voyage through the Design Patterns galaxy takes us to the Adapter design pattern, another of the design patterns found in the GoF catalog. We will find this design pattern most useful once the maintenance cycle has begun on software components.

It might not have been obvious, but your code was implementing a specific SSIS design pattern using your metadata and BimlScripts. With the same metadata and modified BimlScripts, you could implement totally different patterns with altered semantics, performance characteristics, and much more. After implementing multiple such patterns, you might even want to create a mechanism to select the desired pattern for a given transformation through the metadata itself. In fact, let’s go ahead and do that right now.

The next stop on your voyage through the Design Patterns galaxy takes you to the Visitor design pattern, another of the design patterns found in the GoF catalog. You will find this design pattern most useful once the maintenance cycle has begun on software components.

High availability in a Kubernetes cluster is implemented using various parameters. High availability of master controllers would provision multiple master controllers. High availability of etcd would provision multiple etcd nodes. High availability of public DNS would provision multiple public DNSes. In a cloud-native application, availability of a cluster would depend on the availability of the region or zone in which the nodes are run. AWS provides various high-availability design patterns, such as Multi Region Architecture, Multiple Cloud Providers, DNS Load Balancing Tier, and Multiple Availability Zones. In this chapter we will discuss the Multiple Availability Zones design pattern as implemented by Kubernetes. Amazon AWS availability zones are distinct physical locations with independent power, network and security and insulated from failures in other availability zones. Availability zones within the same region have low latency network connectivity between them.

The next stop on your voyage through the Design Patterns galaxy takes you to the Iterator design pattern, another of the design patterns found in the GoF catalog. You will find this design pattern useful when you need to access the elements of a structure sequentially without having to know the representation of those elements.

The next stop on your galaxy quest through Design Patterns takes you to the alternative universe known as Design Anti-Patterns. Nothing from this region is registered in the GoF catalog.

The next stop on your voyage through the Design Patterns galaxy takes you to the Lazy Initialization technique, the second of two design patterns you'll encounter that is not registered in the GoF catalog. You will find this design pattern useful in optimizing components.

The next stop on your voyage through the Design Patterns galaxy takes you to the Decorator design pattern, another of the design patterns found in the GoF catalog. You will find this design pattern useful in dynamically applying additional responsibilities to objects.

Writing a driver that can be used from one application to the next can be very helpful to embedded-software developers. Once a driver is written, developers can focus on the application code and not worry about the bits and the bytes. Driver design patterns can be reused not only on the same hardware, but also across multiple platforms with only minor changes required to adjust the driver to access the different memory regions.

The next stop on your voyage through the Design Patterns galaxy takes you to the Factory patterns, a collection of three distinct patterns (only two of which are found in the GoF catalog). You will find these design patterns useful to simplify the creation of class instances.

Android Studio includes a number of popular user interface design approaches, called "patterns," as pre-coded Activity subclasses found in the Create New Project series of dialogs that you used during Chapter 3.

The next stop on your voyage through the Design Patterns galaxy takes you to the Null Object design pattern, the first of two design patterns you'll encounter that are not registered in the GoF catalog. You will find this design pattern useful in reducing conditional logic.

You are about to leave the terrain provided by the basic principles of object-oriented design over which you traveled to arrive in Objectropolis and to reach for the stars in the galaxy known as Design Patterns. You need to acquire some expertise with celestial mapping and cosmic diagramming to help you navigate through this expanse. The Unified Modeling Language provides you with this skill.

The next stop on your voyage through the Design Patterns galaxy takes you to the Memento design pattern, another of the design patterns found in the GoF catalog. You will find this design pattern useful when you need to be able to reset the internal state of an object to some previous setting.

The next stop on your voyage through the Design Patterns galaxy takes you to the Flyweight design pattern, another of the design patterns found in the GoF catalog. You will find this design pattern useful in optimizing components.

The next stop on our voyage through the Design Patterns galaxy takes us to the State design pattern, another of the design patterns found in the GoF catalog. We will find this design pattern useful when we need to make an object behave differently based on its internal state.

Design patterns capture solutions that have developed and evolved over time. Hence, they aren’t the designs people tend to generate initially. They reflect untold redesign and recoding as developers have struggled for greater reuse and flexibility in their software. Design patterns capture these solutions in a succinct and easily applied form.

The next stop on your voyage through the Design Patterns galaxy takes you to the Chain of Responsibility design pattern, another of the design patterns found in the GoF catalog. You will find this design pattern useful when you need to perform specific processing but want to avoid tight coupling between the requester and the servicer.

The next stop on your voyage through the Design Patterns galaxy takes you to the Command design pattern, another of the design patterns found in the GoF catalog. You will find this design pattern useful when you want to trigger the execution of an activity without having to know what the activity is.

In this chapter, we have chosen to present the most common problems that could occur in big data applications. One of best solutions to these problems is to use design patterns. Research contributions in functional programming continue to be made in this area, including attempts to make functional versions of OOP design patterns. Haskell is a very good programming language for big data, but some of patterns have implementations only in object-oriented programing languages. This is not an impediment for using both Haskell and design patterns, however, because they could be easily made interoperable, as you will see in this chapter. A good design pattern reference is Design Patterns: Elements of Reusable Object-Oriented Software by Erich Gamma, Richard Helm, Ralph Johnson, and John Vlissides (also known as the Gang of Four) (Addison-Wesley Professional, 1994).

The next stop on your voyage through the Design Patterns galaxy takes you to the Observer design pattern, another of the design patterns found in the GoF catalog. You will find this design pattern useful in situations where one class needs to be kept aware of changes occurring in another class.

The simple factory is not an design pattern you find in the original 90s Gang of Four design patterns book. Yet it is an extremely useful way to create objects—so useful that I made a chapter for it.

Modern programming languages such as C# are object oriented in nature. The C# language allows you to think and program in terms of classes and objects. However, knowing C# language keywords and features is just one part of the story. Equally important is knowing how these features can be put to use in the best possible way so as to result in a better quality code base and ultimately help in building software that is robust, flexible, maintainable, and extensible.

In Angular Material, we have used multiple controls and elements that adapt Material Design principles and approaches. FAB is a popular component following Material Design principles. The speed dial among FAB controls is widely used in Material Design applications.

Gang of Four (GoF) patterns are classified into three categories: creational, structural, and behavioral. In this chapter, you will begin by dissecting a few creational patterns. As the name suggests, creational patterns are design patterns that deal with creation of objects, or object instantiation. The C# language uses the new keyword to instantiate an object of a class. Typically, you use the new keyword wherever that object is being utilized. However, this means you must specify a concrete type name at that location. In certain real-world scenarios, as you will learn in this and the next chapter, it becomes necessary to isolate the object instantiation logic and code from the class that utilizes the object. That’s where creational patterns come into the picture.

We have finished the interface for our app! We have all of the views in place; we just need the code behind them now. In Chapter 4, we discussed design patterns; specifically MVVM, which is the design pattern we use to build the Grocery App. We could use pure MVC with this app, but I wanted to show you how we can achieve a very clean and concise app using this pattern.

In the previous chapter, you learned the adapter, bridge, composite, and decorator design patterns.

Spark Streaming applications by design are stateless and side-effect free: running the same application an infinite number of times results in the same behavior and output. Similar to functional programming, this simplifies debugging and reasoning about the state of a program, because input and output paths are deterministic. Although side-effect-free applications have many advantages, in distributed systems side effects cannot be completely avoided, especially when interfacing with external systems. For this reason, Spark Streaming provides a primitive called foreachRDD, which is the Swiss Army Knife of side effects for micro-batch processing. This chapter introduces design patterns for enabling side effects in Spark Streaming applications.

Continuing our journey through behavioral patterns, this chapter will dissect the mediator, memento, and observer design patterns.

In this chapter, we’re going look at web application (or web app, for short) frameworks—libraries of code that provide a easily reusable structure and design patterns for developing web applications. If you want to develop something useful for the Web, you’ll probably find a web application framework very useful, and Ruby has a wonderful selection of them, of which we’ll look at two: Rails and Sinatra.

Design patterns are a great way to make your code functional, readable, and extensible. There are some patterns that are easier and require less code in Groovy compared to Java.

Most problems we encounter as programmers have been handled time and again by others in our community. Design patterns can provide us with the means to mine that wisdom. Once a pattern becomes a common currency, it enriches our language, making it easy to share design ideas and their consequences. Design patterns simply distill common problems, define tested solutions, and describe likely outcomes. Many books and articles focus on the details of computer languages, the available functions, classes and methods. Pattern catalogs concentrate instead on how you can move on from these basics (the “what”) to an understanding of the problems and potential solutions in your projects (the “why” and “how”).