The real power of patterns is the ability to raise your level of thinking. Have you had an experience in which this was true? Encapsulation is best thought of as any kind of hiding. This can mean hiding data, or behavior, or implementations, or derived classes, or any other thing. d. A subclass reference can be assigned to a superclass variable, but a superclass reference cannot be assigned to a subclass variable. one rule, one place says you should implement a rule in only one place. The derivations of an abstract class must use multiple implementations without causing an explosion in the number of classes (p. 151). Using these examples, Has-a example: Sailboat has-a sail (one to many), Uses example: A marina contains one or more Sailboats (p. 32). 2. What do you think is the best way to deal with changing requirements? A consequence is that the pattern allows for preexisting objects to fit into new class structures without being limited by their interfaces (p. 102). In Java, we can achieve abstraction in two ways: abstract class (0 to 100%) and interface (100%).

2. Each arrow is labeled to describe the interaction. 7. Faade defines a higher-level interface that makes the subsystem easier to use. What does this mean? The method declared inside the abstract class is called a move (). (p. 150) An example is a shape object that is responsible for knowing shapes and a Drawing class that is responsible implementing drawing routines. I spend time defining terms related to the CAD/CAM problem. Abstract classes are used to represent the common concept.

We can implement this diagram in Java to avoid code duplication. (p. 121). The rules for determining which driver to use are intermixed with the actual use of the drivers. Individual shapes dont have to know how to do drawings (p. 146). An object should either make and/or manage other objects, or it should use other objects but it should never do both. Suite #362 When the dependencies are fixed (or virtually so), adding an Observer pattern probably just adds complexity. A multiplicity is a factor associated with an attribute. Structural patterns are used for tying together existing functionality. 3. It specifies how many instances of attributes are created when a class is initialized. An IS-A relationship refers to inheritance or implementation. The keyword abstract can be applied to classes and methods. Decoupling of the implementations from the objects that use them increases extensibility. What five features in sheet metal will this system have to address? Understanding them is essential to becoming a successful programmer. Software objects are the actual representation of real world objects. 3.

(p. 297). They represent various aspects of a software application. The essential concept represented by a function. 1. 11. Instead, you need to think about the forces at work in the pattern and then think about ways to implement the intent of the pattern. Implementation: how to implement the pattern in one or more concrete ways. It contains a teacher who tells students where to go. The Abstract Factory requires knowing what classes will be defined. The throw statement passes a value to the catch block. Implementation refers to the objects that the abstract class and its derivations use to put themselves into operation or into service. As you can see in the above diagram, there are many common states and behaviors (common code) between Album and Movie. Copyright Net Objectives, Inc. All Rights Reserved.

Add detail to the conceptual design. They are alive and feel right.

Each has competing systems, speaking different languages. Explain the relationship between commonality/variability analysis and the three perspectives of looking at a problem. 2. There is redundancy amongst the methods It is messy, It has tight coupling: features are related to each other, It has low cohesion: core functions are scattered amongst many classes. Why is this better? They are single, multilevel, hierarchical, multiple, and hybrid. Why or why not? What if the stock keeper creates an album and sets states to negative values? It also frees other objects from worrying whether the object already exists. Narrowing casting (explicit): need explicit conversion. They do not interact with the underlying methods directly (p. 91). In this pattern, there are two kinds of factories. The geometry is stored in objects, each of which represents a feature. 5. Patterns make it possible to reuse solutions. 3. Note that this results in a greater number of smaller methods. GoF Reference: where to look in the Gang of Four book for more information. Can an object contain another object?

Can you think of a situation in which your preconceived notions got in the way of understanding requirements? 2. For example, the class college is made up of one or more student. (p. 110-111). What is the intent of the Observer pattern? 4. Why do they do this? The Analysis Matrix is focused on variations in concepts. What is that? You must invoke all algorithms in the same way (they must all have the same interface). What is another example from real life that illustrates an Adapter? What are the three main types of accessibility that objects can have?

At the conceptual level, find a common label to a set of these variations.

Why do you think the Gang of Four call this pattern Adapter? Alexander uses the term, alive to characterize good designs. What is Alexanders view of how to use patterns? When it comes to choosing how to implement a design, what question do I suggest asking? Alexander discovered that by looking at structures that solve similar problems, he could discern what? I suggest that factories also help in testing. Any kind of hiding. It starts by understanding the concept that a function represents and putting a label onto it. 2. The first solution exhibits four problems. Expand the method and class definitions. You should draw a diagram that represents the concepts in the domain under study. A Class in UML is represented by a rectangle that includes rows with class names, attributes, and operations. 3. (p. 176). Do you agree? The seniormost pattern is the pattern that creates the context for the other patterns. In our context, it means to have one thing behave independently from another (or at least to state explicitly what that relationship is), Abstraction means to generalize or conceptualize: to step back from the more concrete to the more conceptual or abstract. Which patterns described in this book might be present in an Analysis Matrix? Class Diagram helps construct the code for the software application development. Cohesion is how strongly the internal operations of a routine are related to each other. 3. At what level of perspective does the Analysis Matrix operate? Why or why not? Not usually. 3. This is where we use encapsulation. Abstract classes cant be instantiated (cant create objects of abstract classes). Get started, freeCodeCamp is a donor-supported tax-exempt 501(c)(3) nonprofit organization (United States Federal Tax Identification Number: 82-0779546). So when a class implements an interfaces method without specifying the access level of that method, the compiler will throw an error stating Cannot reduce the visibility of the inherited method from interface. (p. 32), Cardinality indicates the number of things that another object can have (p. 36). It is also possible to have an abstract class with no operations declared inside of it. An interface can have only abstract methods, not concrete methods. Dependency indicates that one class depends on another.

2. Casting a reference variable doesnt change the object on the heap but it labels the same object in another way by means of instance members accessibility. Rooms will never separate into a House.

Specification perspective: Specification perspective describes software abstractions or components with specifications and interfaces. Did it succeed? Specifications become abstract classes at the implementation level (p. 120).

How can we convince the compiler like this? (p. 299). What are these rules? Object-oriented programming principles in Java. (p. 17), At the conceptual level, an abstract class is a placeholder for a set of classes. Is it important to understand the users terminology? What are the relationships between these objects? As many as it takes to communicate clearly, and no more (p. 31). 4. 3. Code reuse: the child class inherits all instance members of the parent class. (p. 306). Define encapsulation. The albums price and number of copies cant be negative values. You allow the other object to be responsible enough to figure out what to do. The Sequence diagram is one type of Interaction Diagram in the UML.

2. b. Commonality analysis focuses on finding structures that will not change over time while variability analysis looks for structures that are likely to change. Bertrand Meyer puts this forward as a way to minimize risk when changing systems. Changing requirements is one of the greatest challenges faced by systems developers. Should you ever use switch statements?

They can have constructors, static methods, and final methods. Circle manifests the entire behavior of XXCircle to the system, although with a different interface / way of accessing XXCircle. Class diagram allows inheriting from multiple superclasses. When objects communicate with each other, why is it more appropriate to talk about sending a message than invoking an operation? Keeping the big picture in mind.

NOTE: We can overload the main() method but the Java Virtual Machine (JVM) calls the main() method that receives String arrays as arguments. Think of a building or structure that felt particularly dead.

One example is the example they found from Steve Maguires book, Writing Solid Code. 3. Is it an appropriate name for what it is doing? In what way is the Analysis Matrix similar to Commonality/Variability Analysis? In the course of this book, I have presented many of the essential concepts of object-orientation. Look for what is changing and make a more generic version of it so that you can see what is truly going on in your system and not get caught up in the details. When it comes to applying patterns to a design, we want start with the seniormost patterns first and then work down (p. 203). In the above abstract class notation, there is the only a single abstract method which can be used by multiple objects of classes. It helps for better understanding of general schematics of an application. Lets say that the record shop we discussed above also sells Blu-ray movies. It does this by wrapping the call to new with another conditional test. Cardinality: A Model can have no Features, 1 Feature, or many Features. 4. Is this different than one object containing a data member? Why? 2. (p. 90). The Strategy pattern defines a family of algorithms. What types of objects are used to represent the common concepts? (p. 120), 6. 1. At the end of his book, Christopher Alexander says, At this final stage, the patterns are no longer important the patterns have taught you to be receptive to what is real. What is real, are the relationships and forces described by the patterns. What are the three perspectives for looking at a problem? (p. 151). The technical environment evolves, forcing changes in how to implement. The top box is the name (label) of the class. 2. (p. 118), 3. The bottomline is, the approach espoused by patterns will scale while the original use of inheritance will not.

Allows drawing detailed charts which highlights code required to be programmed. Our mission: to help people learn to code for free. 5. (p. 19). What is wrong with this?

Does the Faade pattern usually give you access to the entire system? To force sub classes to implement abstract methods. It means that I have a class that needs to interact with another class through a certain set of method calls. A class name should always start with a capital letter.

Identify additional patterns that are now suggested. So inside the interface, we dont need to specify public and abstract. (p. 72).

There are two mention different ways to understand objects: data with methods and things with responsibilities.. 1.

What is the value of hiding implementations?

What is the fourth classification that I suggest? We can not retain common code.

It is encapsulation of behavior: it helps objects be less dependent on some other object to do something that will directly impact what that object can do. Student HAS-A StudentId. What are the consequences of the Bridge pattern? What are they? Patterns help with communication between analysts, giving a shorthand terminology. 1. What is the essential challenge of the CAD/CAM problem? Which of the following does not complete the sentence correctly? NOTE: Interfaces only define required methods. This type of relationship is known as aggregation. 2. 3. In this book, that involves Bridge, Decorator, Template, and Observer. The attributes are generally written along with the visibility factor. Implementation: how an individual routine works (code). If this doesn't happen, then the sub class also should be marked as abstract. What is the purpose of a Sequence diagram? What is another example from real-life? However, since the Faade is not complete, certain functionality may be unavailable to the client. Superficiality, Bias, Selection, Misdiagnosis, Fit. The GoF specified three types: Structural, Behavioral, and Creational. They are very complex to understand and to maintain. 1. Clients work with sub-systems through the Faades interfaces.

But you have to be careful not to create global variables. I strongly encourage you to read more related articles on OOP. Favor object aggregation over class inheritance. 2 Consider what should be variable in your design. Give an example. Now, we have covered the basics of object-oriented programming. No Review Questions in this summary chapter. Visibility/access modifiers impact what gets inherited from one class to another. In this case, we can convince the compiler by saying at runtime, mary will be Student type, so please allow me to call it. Implementation perspective: This type of class diagrams is used for implementations in a specific language or application. Provide a unified interface to a set of interfaces in a sub-system (p. 87). Design to interfaces, not to implementations (p. 171).

They do not have to be conceptually similar. One uses the Factory Method to defer responsibility to subclass objects. (p. 293). Adapter frees me from worrying about the interfaces of existing classes when doing a design. An instance of one class HAS-A reference to an instance of another class. 4. How has it been used in Java, C#, and C++? What do the rows of the Analysis matrix represent? Aggregation indicates a relationship where the child can exist separately from their parent class. It can lead to decreased cohesion because an object depends on or more other objects to ensure work is done before it can successfully continue. I put forward the idea of a fourth category of patterns, that somewhat includes patterns from other categories. Creating a class diagram is a straightforward process. No constructors are allowed here.

top. A class that implements an interface but does not declare all of the interface's methods must be declared: A class that implements a decorated interface must be a subclass of a class that implements the original interface. (p. 124). In the Faade pattern, how do clients work with subsystems? Polymorphism is required at the geometry extractor level because the expert system needs to know what type of features it is dealing with: slot, hole, etc. What reasons do they give? 1. What are the key elements in the description of a design pattern?

Relate the approach to design starting with CVA with Alexanders approach.

2. The developers understanding of what is possible and what is needed evolves as they become familiar with the domain and with the software. There are many options on them: how to pay, the type of gas to use, watch an advertisement. The Adapter provides a translation to these methods. It is often used in conjunction with other design patterns. I advocate thinking about responsibilities rather than functions. There is a fundamental weakness in functional decomposition when it comes to changes in requirements. (p. 119). How you choose to implement the factory variations is not specific to the pattern. The first concrete sub class of an abstract class must provide implementation to all abstract methods. What is the basic problem being solved by the Bridge pattern? There are 6 objects shown: Main, ShapeDB, Collection, shape1:Square, shape2:Circle, and Display. What is the one true thing about requirements? If they attempt to assign negative values for the albums price and number of copies, well assign them as 0.0 and 0. Program to an interface, not an implementation. 1. 1. This abstract class method can be used by any object such as a car, an animal, robot, etc. I state that experienced developers even more than inexperienced ones often focus on entity relationships too early, before they are clear what the right entities are. To give you an idea about classes and objects, let's create a Cat class that represents states and behaviors of real world Cat. Class Diagram Illustrates data models for even very complex information systems, It provides an overview of how the application is structured before studying the actual code. Is it an appropriate name for what it is doing? It certainly reduces the maintenance time. One definition is the interrelated conditions in which something exists or occurs. Is this an effective way to deal with changes in requirements?

How do you decide which possibilities to handle now and which to be ready for in the future?

It is important to explore for variations early and often.

In fact, data types are also objects, so there is no difference. In the CAD/CAM problem, I reject the Abstract Factory as the seniormost pattern. In both cases, I create an intermediary object with interfaces that my system wants to use and that has responsibility for mapping that to the preexisting class. I quote Alexander, But it is impossible to form anything which has the character of nature by adding preformed parts. What does Alexander mean by this?

4. One example of the Observer pattern from outside of software is a radio station: It broadcasts its signal; anyone who is interested can tune in and listen when they want to. Is there ever a time when you should go ahead and dive into the details? What are three reasons for studying design patterns? 4. 1. Pumps at gasoline stations in the US can be very complex. 1. They provide loose coupling: objects are independent from one another. How do you know when to use the Abstract Factory pattern? The Strategy pattern controls a family of algorithms. However, I want to insulate my system from having to know specifics of the particular concrete object being instantiated. (p. 38). (p. 189). What forces are at work. Assigning a subclass reference to a superclass variable is safe: because the subclass object is an object of its superclass. What is wrong with this? Good design requires keeping what in mind? 17. Why is this pattern called a factory method?. (p. 204). I drew exactly the opposite conclusion. Do you agree with their logic?

Objects pass messages to each other. What are some alternatives for handling new requirements? 2. The intent of the Adapter is to match an existing object that is beyond your control to a particular interface. (p. 17).

This modeling method can run with almost all Object-Oriented Methods. This is one type of encapsulation. The name given to the class diagram must be meaningful. A classroom is used to describe objects in a system. An abstract is useful for identifying the functionalities across the classes. Look at objects in terms of their responsibilities rather than their behaviors. How does this affect your view of the use of inheritance in an object-oriented system? Give an example, Variation represents special cases that complicate understanding. Suppose we have an abstract class called as a motion with a method or an operation declared inside of it. Define the one rule, one place strategy. It is efficient to use this abstract class method with an object because no implementation is provided for the given function. However, there are multiple security layers that any ATM system needs to pass. The Faade simplifies the use of the required subsystem. Repeat. In this chapter, the factories mentioned are Builder, Factory Method, Prototype, and Singleton. 3. (p. 309). (p. 163). The Gang of Four says that the intent of the Bridge pattern is to decouple an abstraction from its implementation so that the two can vary independently. What does this mean? Clearly, there is a relationship between Bridge and Adapter. What is the essential ability required by the CAD/CAM application? A pattern defines relationships between the entities in his problem domain (p. 191, 192) This is why define a pattern as a solution to a problem in a context. Polymorphism is the ability of an object to take on many forms. Why or why not?

The three perspectives are the Conceptual perspective, the Specification perspective, and the Implementation perspective. mary is a Person type reference variable and new Student() will create a new Student object. Have you ever seen a courtyard or entryway in a house or building that has felt particularly dead or uninviting? 4. What are the consequences of the Adapter pattern? Give an example. (p. 19). Polymorphism in OOP occurs when a super class references a sub class object. We can use it in any way for multiple objects.

What is the difference between the V1 system and the V2 system? What is a reason for encapsulating an entire system using the Faade pattern? The Template Method pattern is applicable when there are different, but conceptually similar processes. Only inherited methods may be overridden (must have IS-A relationship). Reading widely is an important discipline. I assert that Alexanders general rules (design by starting with the context) still apply. There are mainly three kinds of relationships in UML: A dependency means the relation between two or more classes in which a change in one may force changes in the other. What terms do I suggest using when it comes to software? 1. 1. Why or why not? It is a template to create various objects and implement their behavior in the system. If the interface of that other class does not provide these method calls, the Adapter sets up a new interface to do the translation. For example, if college is composed of classes student. The Gang of Four says that the intent of the Abstract Factory pattern is to provide an interface for creating families of related or dependent objects without specifying their concrete classes. What does this mean? (p. 105). It is too limited to define an abstract class as a class that does not get instantiated. Name in the form objectname:classname. The classroom contains students who are responsible for their own behaviors: how to move from here to there, how to go from class to class. If it has, the method simply returns a reference to the object. In this example, the relationship between student and college is shown which is studies. What is the intent of the Faade pattern? But Adapters interfaces cannot be determined without Bridge.

Public, private, protected and package are the four visibilities which are denoted by +, -, #, or ~ signs respectively. Give examples. CVA does not speak about best-practices, leaving that to the designers imagination. 3. Concrete instances are used to represent the variations. 1 Gamma, E., Helm, R., Johnson, R., Vlissides, J., Design Patterns: Elements of Reusable Object-Oriented Software, Reading, Mass.

1. Let's move on to the principles of object-oriented programming. What are the consequences of the Strategy pattern? It is quite different from procedural programming where you retain control of what to do next, and thus might calling a method or invoke an operation in another object.

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