...设计模式总结： Observer pattern： The observer pattern is a software design pattern in which an object, called the subject, maintains a list of its dependents, called observers, and notifies them automatically of any state changes, usually by calling one of their methods. It is mainly used to implement distributed event handling systems. The Observer pattern is also a key part in the familiar Model View Controller (MVC) architectural pattern. Singleton pattern: In software engineering, the singleton pattern is a design pattern that restricts the instantiation of a class to one object. This is useful when exactly one object is needed to coordinate actions across the system. That is you only want one object and use it in multiple places. there are two ways of implement singleton pattern, create database connection and login file can be a very good example of singleton pattern: here we will look at create database connection: old ways of implementation: (lazy loading) private static Database instanceOld; public static Database getInstanceOld(){ if(instanceOld == null){ instanceOld = new Database(); } return instanceOld; } since the old way of singleton implementation has thread safe problem, for example: there are several thread invoke getInstanceOld() method and there will be several instance created. new way: (early loadings) private static Database instance = new Database(); private Database(){//private constructor } public static Database getInstance(){ ...
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...Design Patterns Jon Jensen CSS/422 July 2, 2012 Ken Murphy Design Patterns Out of all of the different design patterns the three that this paper will focus on will be the Adapter, Model–View–Controller or (MVC), and Data Access Object or (DAO). This paper will compare all three of them and try to show which one will be used for what type of project and why it was chosen to do it. The first design that we will look at is the Adapter design which helps reuse an object or a method by adapting its interface into a more common one. The adapter pattern translates one interface for a class into a compatible interface for a new class. An adapter allows the classes to work together when they normally could not because of their incompatible interfaces. The adapter also transforms data into an appropriate form. For example, if multiple Boolean values are stored as a single integer but the client requires a 'true'/'false', the adapter would extract the appropriate values from the integer. Another example would be transforming the format of a date for instance MM/DD/YYYY to DD/MM/YYYY or YYYY/MM/DD). The adapter design is about creating an intermediary abstraction that translates the old component to a new system. The Adapter pattern lets incompatible classes work with the interface of one class by converting it into the interface that is expected by the clients. For instance a socket wrench is a good example of an Adapter. A socket will attach to a wrench as long as the size of...
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...Design Patterns CSS/422 September 2, 2013 Design Patterns When developing enterprise software there are several design patterns to choose from. The factory method, abstract factory method, dispatcher data access object (DOA), and model-view-controller (MVC) are design patterns that play an important role in the software development process. By implementing proven design patterns the development process is accelerated and more efficient. The reuse of these patterns also prevents the occurrence of the more subtle issues that may cause significant problems while improving the code readability for architects and coders who are familiar with the design patterns. For effective software design, the consideration of issues that may not become apparent until the latter stages of implementation is essential (SourceMaking, 2012). Factory Method The factory method design pattern creates a family of related objects instantiated by subclasses (University of Phoenix, 2010). This design pattern creates objects without detailing the class of object to be created. The factory method design pattern defines a separate method for the creation of objects by employing subclasses to override the derived type of object being created. In addition, the factory method makes a design more customizable while only slightly increasing its complexity. While other design patterns require new classes, the factory method simply necessitates a new operation (SourceMaking, 2012). Abstract...
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...Command Design Pattern Agenda * What is the Command Desgn Pattern (CDP) * Object Interaction and Command Object Hierarchy * Command Pattern generic UML * Recorded demonstration * Java example code * What are the benefits/drawbacks of the CDP The intent of this presentation is to provide a walk through and recorded demonstration of the command design pattern. What is the Command Design Pattern? * A Behavioral design pattern * An object is utilized to represent and encapsulate information * The information includes method name, object owning method, and method value parameters * The information can be called immediately or at a later time The command pattern is a behavioral design pattern in which an object is utilized to represent and encapsulate information (Banas, 2012). The interesting thing about the command design pattern is that it can allow one to store lists of commands which can be called immediately or at a later time. What is the Command Design Pattern? * Client specifies which command to run when the execute() method is invoked on one of the encapsulated methods * An object named “Invoker” transfers the Command to a separate object named “Receiver” which executes the correct code The command pattern allows the client to determine which command to run when the execute method is invoked in the command interface (Kuchana, 2004). After the command is “invoked” to execute, he concrete command that is identified transfers...
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...Term paper On Design patterns Advanced topics in software engineering CSC 532 Submitted by:- Harpreet Singh Abstract:- Design patterns, a standard solution to problems in object oriented software engineering, are considered to be a well formed language to represent software design. Their benefits have been widely acknowledged by software professionals throughout the world. Design patterns can be classified according to multiple criteria the most common being the type of problem they solve. Till today many design patterns have been established and many more are being found as time passes. Patterns capture knowledge from various parts of software developing. Design patterns are helpful to the designers in a way that they represent the collective wisdom and experience of the community and their implementation leads to better quality software and also a novice designer does not find it difficult to understand the systems functionality. A very important advantage of design patterns is the fact that they speed up the development process by providing an almost ready-made solution that has been used earlier and proved to be efficient. Another advantage is that they allow for a generalized solution that does not depend on understanding a specific design problem from all its aspects, and thus ease reusing this solution. Apart from that they help the new developers to ignore traps and pitfalls which have earlier been learned by other developers by costly experience...
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...generic system represents all the systems whether they are physical, sentient or more abstract. All the system follows the rules of the generic system. This system can be implemented during software development processes which helps all the processes to adapt to every software environment easily. Introduction: In software development , design phase is one of the important phase which takes lots of time and it is very hard to satisfy the end user regarding designing. Therefore this designing phase starts from beginning the of software development process till the end of the project. Therefore keeping in mind regarding the user needs and evolvement of new techniques each day, the generic system of design and development is introduced. By making the system generic, it becomes very easy for any of the software development company to adapt with the new working environment. Problem description: To develop a generic system design that helps to monitor the entity life history of any particular enitity and to show how this design is used in the administration system of academic conference. Objective: The main objective is to make a generic system design that can be implemented in the administration of any of the organization with few customization. => The generic system will be used to monitor the administration system and to keep track of the progress of any event in the administration system. =>To make the progress chart that helps to give clear idea about progress in the event. ...
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...Design Patterns Elements of Reusable Object-Oriented Software Produced by KevinZhang Design Patterns: Elements of Reusable Object-Oriented Software Contents Preface to CD ........................................................ 5 Preface to Book ...................................................... 7 Foreword ............................................................. 9 Guide to Readers .................................................... 10 1 Introduction ...................................................... 11 1.1 What Is a Design Pattern? ...................................... 12 1.2 Design Patterns in Smalltalk MVC ............................... 14 1.3 Describing Design Patterns ..................................... 16 1.4 The Catalog of Design Patterns ................................. 18 1.5 Organizing the Catalog ......................................... 21 1.6 How Design Patterns Solve Design Problems ...................... 23 1.7 How to Select a Design Pattern ................................. 42 1.8 How to Use a Design Pattern .................................... 44 2 A Case Study: Designing a Document Editor ......................... 46 2.1 Design Problems ................................................ 46 2.2 Document Structure ............................................. 47 2.3 Formatting ..................................................... 53 2.4 Embellishing the User Interface ................................ 56 2.5 Supporting Multiple...
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...Design Patterns By XXX Agenda § Model-View-Controller (MVC) § Observer Pattern Model-View-Controller Design Pattern (MVC) What is MVC? § MVC stands for Model-View-Controller. § MVC originated from SmallTalk in the 1970s. § Common pattern which is now used for web applications as well as the standard pattern used for iOS applications. § MVC is a proven design pattern to create a complex application that enforces separation of concerns, provides loose coupling and provides an avenue to create testable code. Model-View-Controller Controller Model Model never talks to the View View Model Responsibilities § The “M” in MVC. § Consists of application data, business rules and logic, domain specific classes/methods/functions. § Example: Hydrating model objects like Person object from a database. § Models can broadcast messages (notifications) if other objects update the model (subscribe/unsubscribe pattern). Controller Model Model never talks to the View View Controller Responsibilities § The “C” in MVC. § The traffic cop that communicates between the Models and the Views. § The controller understands how to take the models and provide them appropriately to the view. § The controller also understands how to update the model based on user interactions from the view. Controller Model Model never talks to the View View View Responsibilities § The “V” in MVC § Any output that is visible to the user. (ex...
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...Introduction Design Patterns In Software Engineering we use different design pattern as a general solution to commonly occurring design problems. Originally 23 design patterns were introduced by 4 authors in their book, who came to be known as “Gang of four.” The 3 Basic types of design patterns are: Creational patterns Structural patterns Behavioural patterns In this term paper we’ll discuss about structural design patterns. Structural patterns Structural Design Patterns are design patterns that deals with Class and Object composition. It does the following things: 1. It uses the concept of interface by using inheritance. 2. It defines object in such ways as to use them for multiple purpose. 3. It helps to relate various entities using different means by finding their relationship with each other. Various types of Structural Design Patterns are given below: Adapter: It acts as a translator to match interface between two incompatible classes. Bridge: Separates abstract interface from its implementation, which provides a cleaner implementation of real-world objects and allows the implementation details to be changed easily. Composite: used when creating hierarchical object models, this allows clients to treat individual objects uniformly. Decorator: It extends the functionality of individual objects by wrapping them with one or more decorator classes. These decorators can modify existing members and add new methods and properties at run-time. Facade: It...
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................................................................................................................ 4 Provide the UML diagrams for the given problem with clear explanations on the design decisions. Derive detailed Use Case diagram, Class diagram & a sequence diagram. Whenever necessary document the relevant assumptions you made. ...................................................................................... 4 TASK B ....................................................................................................................................................... 7 Provide an alternative OO design for the same problem ......................................................................... 7 Object Oriented Known as Methodology or paradigm to design a program using classes and objects. It simplifies the software development and maintenance. ......................................................................... 7 TASK C ....................................................................................................................................................... 9 There are many system design patterns available in system development. Critically evaluate singleton, factory and abstract factory design patterns and apply the most suitable design pattern for your system development................................................................................................................................. 9 TASK D .........................
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...Analyzing Anti-pattern Detection Southern Methodist University Abstract A design pattern is a well-understood, reusable design fragment used to solve a commonly occurring problem in software development. Whereas, antipatterns are common design pitfalls that provide poor solutions to recurring design problems. Developers may unwillingly introduce anti-patterns in their software systems due to time pressure, lack of skills, communication or understanding. Anti-patterns have a negative effect on the comprehension and maintainability of a software system, and thus, understanding and detecting Anti-patterns provides the knowledge to prevent or recover from them. This paper discusses the anti-patterns of object oriented design, their symptoms, and consequences and issues related to their detection. This study also discusses some of the tools and approaches that are currently being developed and used in the software industry to detect anti-pattern. Towards the end, this paper also highlights some of the problems that are still open, to drive future research direction in this field. 1. Introduction Now-a-days, most of the software projects deal with large number of components that make the software more complicated and hard for novice designers to design. A design pattern is one of the most simple and powerful techniques used to improve the software design. Unfortunately, due to a number of market/customers constraints, anti-patterns may get introduced...
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...is decided to change vendors. Vendor2 is selected which has different method names. Example (cont’d) The Client must be modified in order to adapt to the new vendor. What was the problem? The Client class encapsulates some portion of application logic, which is intertwined with the Vendor class. This causes the strong coupling/ dependence. Thus, modifying the Client code to adapt to the new vendor could result in errors being injected into the application logic. How do we mitigate this situation where we have a Client coded against a Vendor, where the Vendor will change? Two helpful design principles • Identify the aspects of your application that vary and separate them from what stays the same. • Program to an interface, not an implementation. • The first principle suggests that we separate the application logic from the code tied to the vendor. • The second design principle indicates how we may achieve that. • We program against an abstraction of all Vendor classes and then use an Adapter to encapsulate vendor specific code required to implement...
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...CORPUS CHRISTI SCHOOL END OF THIRD TERM EXAMINATION SECTION A (50 MARKS) 1) How loud or soft a music is termed ………………………….. a. Dynamic b. Rhythm c. pitch 2. Using alphabet to create patterns by arranging and pasting is called …………………………….. a. letter colle b. frottage c. drawing 3. The combination of long and short sounds in music is called…………………….. a. dynamics b. rhythm c. pitch 4. In music how high or low the music is termed ………………………………. a. dynamics b. rhythm c. pitch 5. In dancing when someone lift the arm high and wave in the air it can be referred to as ….............. a. instruments b. ensemble c. gesture 6. A design or a pattern used as a decoration is called ………………………………… a. appliqué b. pattern c. motif 7. A type of needle work in which small pieces of fabric are sewn or stuck in a pattern onto a larger piece is ……………………………….. a. appliqué b. pattern c. motif 8. ………………………………… is the expression of feelings and ideas using tools like pencil, crayon, and charcoal on a flat surface. a. Drawing b. Frottage c. Letter colle 9. A way in which something such as lines, shapes, colours are arranged to form a design is called ……………………………………….. a. colouring b. drawing c. pattern making 10. Rubbing the surface of paper against a rough surface using pencil, crayon or charcoal is called ………………………………………… a. letter colle b. frottage c. copying 11. Which of these is used for measuring? a. needle b...
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...of wallpaper manufacturers as these manufacturers must not only produce a good that is highly valued but is also offered at a reasonable cost. When wallpaper pattern designs become obsolete, markdowns are necessary to help get rid of this old inventory. These markdowns are a key factor in the recent trend of decreasing net income. Since Chabot has made the decision to reimburse retailers for markdowns, Chabot’s total profit margin is reduced relative to the markdown reimbursement costs. Markdown costs have nearly tripled since 2006 and show no sign of slowing down because every four months a new pattern is introduced which creates less demand for the older patterns. The markdowns can be traced back to poor forecasting. Chabot’s forecasting is causing them to build up a very undesirable level of obsolete inventory. This increasing number of obsolete inventory also has a negative effect on inventory turnover. Retailers are very concerned with this turnover rate because it carries a heavy cost on inventory holding. Retailers are threatening to remove Chabot’s products from their shelves in order to make space for products with higher turnover rates which will help minimize inventory costs for the retailers. Keeping up with demand is another issue for Chabot. Chabot is unable to keep a steady supply of its successful patterns which is unacceptable to loyal...
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...Renaissance and Baroque styles and is a good example of the transition into more romantic paintings. The composition of this piece is well balanced. Although the subjects are cropped, they are cropped on both the right and the left side, making the painting horizontally balanced. This also gives an effect to the viewer that there is more depth to what is shown; giving the feeling that the viewer is almost in the battle with them. These cropped subjects nicely frame the triangular composition of the people fighting in the middle who are piled on top of each other. The triangle’s base begins with figures on the floor and rises to a point with other figures standing so the viewer can see the actions of every character. Use of geometric patterns are also used in the lighting to lead the eye around the composition. This is seen in an upside down triangle. Our eyes first catch attention in the foreground, where there is a tenebristic spotlight effect. They then move to the next most lit spot to the right in the mid-ground, and then to the left. This lighting moves the viewer’s eyes through the depths of the picture plane and also reveals systematically what is happening in this painting. From this movement, you can see that women are placed into the battle. As your eye moves in the directed places, you see the women being taken by the centaurs, relaying what the battle is possibly about. Many of the subject’s arms are raised to create movement as well as action. The arms direct our...
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