Design Patterns: Elements of reusable object-oriented software (the book "design patterns"), co-authored by Erich Gamma, Richard Helm, Ralph Johnson, and John vlissides (Addison-Wesley, 1995 ). These authors are often referred to as "Group of Four (Gang of Four)", and this book is also known as "Group of Four (or gof.
Design Patterns: Elements of reusable object-oriented software (the book "design patterns"), co-authored by Erich Gamma, Richard Helm, Ralph Johnson, and John vlissides (Addison-Wesley, 1995 ). These authors are often referred to as "Gang of Four", and this book is also known as "four-person group (or gof.
The largest part of the book "design patterns" is a directory that lists and describes 23 design patterns. In addition, this ticket has recently added some categories. The most important thing is to extend the scope to more specific problem types. For example, Mark grand wrote strated with UML in patterns in Java: a catalog of reusable design patterns (later in pattern Java) and core J2EE patterns co-authored by Deepak Alur, John crupi, and Dan malks: best practices and design strategies focuses on multi-layer applications using Java 2 Enterprise TechnologyProgram.
The Research on Software Design Patterns has created a book that may be the most influential in Object-Oriented Design: design patterns.
The gof design model is a "bridge"
As far as the Java language system is concerned, the gof design mode is an implicit "bridge" between Java basic knowledge and J2EE framework knowledge ".
There are more and more developers who are familiar with Java, but there are not a few programmers who have been wandering at the language level. There are not many applications that really grasp interfaces or abstract classes in Java. We often say that those technologies are only suitable for large projects, avoid or ignore them. In reality, Java interfaces or abstract classes are the core of the true embodiment of Java ideas, and you will see their changing magic in the gof design patterns.
On the surface, the gof design pattern seems to be a specific "technology", and new design patterns are constantly emerging. The design pattern has its own development track, which seems to be similar to J2EE. net and other technologies have nothing to do!
In fact, the gof design pattern is not a specific "technology", it tells the idea, it not only shows the flexible application and wisdom of interfaces or abstract classes in actual cases, so that you can really grasp the application of interfaces or abstract classes, so as to step forward on the basis of the original Java language. More importantly, the gof design pattern repeatedly emphasizes a purpose for you: make your program as reusable as possible.
This is actually a challenge to the extreme: the demand for software is changing infinitely, and the plan is not changing fast, but we still need to find something that remains unchanged and separate it from what is changing, this requires great wisdom and experience.
The gof design model is a milestone that begins to be explored in this respect.
J2EE is a framework software. What is Framework software? It is different from the Java APIs we used previously, which belong to toolkist (Toolkit). It is no longer passively used or called, but deeply involved in a field, the purpose of the framework software design such as J2EE is to first define the unchanged things in a field, such as the overall structure and some main responsibilities (such as database operation Transaction Tracking security ), the rest is the changing things. The specific changing requirements for specific applications in this field are what J2EE programmers need to do.
It can be seen that the design mode and J2EE are in the same ideological and motivation,
1. The design pattern is more abstract. J2EE is a specific product.CodeWe can see that the design pattern will generate specific code for each application.
2. the design pattern is a smaller architecture than the framework software such as J2EE. Many specific programs in J2EE are completed by the application design pattern. When you go deep into the internal code Research of J2EE, this is especially obvious. Therefore, if you do not have the basic knowledge of design patterns (gof's design patterns), it is difficult for you to quickly understand J2EE. I cannot understand J2EE. How can I use it flexibly?
3. J2EE is only a framework Software suitable for enterprise computing applications, but the gof design mode can be used for almost any application! Therefore, the gof design mode should be one of the important theoretical foundations of J2EE.
Therefore, the gof design mode is an implicit "bridge" between Java basic knowledge and J2EE framework knowledge ". Why is it implicit?
The gof design model is a hidden "bridge"
Many people did not notice this. After learning the Basic Java language, they went to learn J2EE directly. Some even ran away and used Weblogic and other specific J2EE software directly. After a while, they found that, it's easy to use, but do you really understand J2EE? Is your application in specific cases also extending the idea of J2EE?
If you can't extend the idea of J2EE well, wouldn't you be a blockbuster? It's wise to realize that J2EE is not suitable for everyone, at least, however, we need to use J2EE in a proper place. Only by understanding the essence of J2EE framework software can you use Java flexibly to solve your problem, you can even build your own enterprise framework. (We cannot always use frameworks set by others. Why cannot we have our own frameworks ?)
Therefore, you must first master the gof design model. Although it is implicit, it cannot be crossed.
Interesting insights on 23 Design Patterns
The author uses a simple language to compare the 23 Java models, which has a good inspiration.
1. Factory-try to catch up with mm. The chicken wings of McDonald's and the chicken wings of KFC are what mm loves. Although the taste is different, whether you take mm to McDonald's or KFC, just say "four chicken wings" to the waiter. McDonald's and KFC are factory for chicken wings production.
Factory model: the customer class and the factory class are separated. A consumer needs a product at any time and only requests from the factory. Consumers can accept new products without modification. The disadvantage is that the factory class must be modified when the product is modified. For example, how to create and provide data to clients.
2, BUILDER-MM is the most love to hear is "I love you" this sentence, to see different places of mm, to be able to use their dialect to say this sentence to her oh, I have a multi-language translation machine with a key for each language above. To see mm, I only need to press the corresponding key, it will be able to say "I love you" in the corresponding language, and foreign mm can also easily develop, This is my "I love you" builder. (This must be better than the US military's translation server in Iraq)
Construction mode: separates the internal appearance of a product from the product generation process, so that a building process generates product objects with different internal appearances. The construction mode allows the product's internal appearance to change independently, so that the customer does not have to know the details of the product's internal composition. The construction model enforces a step-by-step construction process.
3. Factory method-ask mm to go to McDonald's for a hamburger. Different mm has different tastes. It is annoying to remember every one. I usually use the factory method mode, take the mm to the waiter and say "I want a hamburger". What kind of hamburger should I ask the mm to tell the waiter directly.
Factory method mode: the Core factory category is no longer responsible for the creation of all products. Instead, it submits the specific creation work to the subclass to become an abstract factory role, it is only responsible for providing the interface that must be implemented by a specific factory class, without touching the details of which product class should be instantiated.
4. Prototype-chat with MM via QQ, so I must talk about some affectionate words. I have collected a lot of emotional words, and I just need to copy the words and put them in QQ, this is my prototype. (100 yuan a copy, do you want)
Original Model mode: specify the type of the object to be created by giving a prototype object, and then create more objects of the same type by copying the prototype object. The original model mode allows you to dynamically add or remove product classes. The product class does not need to have any predefined level structure. The original model mode applies to any level structure. The disadvantage is that each class must have a clone method.
5. Singleton-I have 6 beautiful wives. My husband is me. I am sigleton, our husband. All they need to say is "husband, that's me (I had a dream just now. How can this be a good thing)
Singleton mode: Singleton mode ensures that a class has only one instance, and instantiate the instance and provides the singleton mode to the entire system. The Singleton mode can only be used when there is a real "Single Instance" demand.
6. adapter-I met Sarah, a beautiful girl from Hong Kong at a friend's party. But I can't speak Cantonese, and she can't speak Mandarin. I have to turn to my friend Kent for help, as an adapter between me and Sarah, Sarah and I can talk to each other (I don't know if he will play with me)
Adapter (transformer) mode: converts an interface of a class into another interface that the client expects, so that the two classes that cannot work together due to interface mismatch can work together. The adaptation class can return a suitable instance to the client based on the parameters.
7. Bridge: mm in the morning. Good morning. mm in the evening. Good evening. mm in new clothes. Nice clothes. New hair styles, say your hair looks pretty. Don't ask me the question "How to say mm has a new hairstyle in the morning". Just use bridge to combine it.
Bridge Mode: Abstraction and implementation are decoupled so that the two can change independently, that is, the strong association between them becomes weak Association, that is, the combination/aggregation relationship is used between the abstraction and implementation of a software system, rather than the inheritance relationship, so that the two can change independently.
8. Composite-Mary has a birthday today. "You want to give me a gift for my birthday ." "Well, all right, go to the store and pick it for yourself ." "This T-shirt is very beautiful. Buy it. This dress looks good. Buy it. This bag is also good. Buy it ." "Hey, I bought three items. I only promised to give one gift ." "What, a T-shirt with a skirt and a bag, just like a set, miss, please pack it ." "……", Mm will all use the composite mode. Will you?
Merging mode: the merging mode organizes objects into the tree structure and can be used to describe the relationship between the whole and the part. The merging mode is a tree structure mode for processing objects. The merging mode shows the relationship between the part and the whole in a tree structure. The merging mode allows the client to view individual component objects in the same way as the compositing objects composed of them.
9. After decorator-Mary finishes her birthday in sarly's turn, do not ask her to pick it up by herself. Otherwise, the meal fee will surely end up this month and take out the photo I took on the top of Huashan last year, write "the best gift is your FITA" on the back, and then buy an image frame in the street Gift Shop (mm for gift sale is also very beautiful ), mike, who is next door to art design, designed a beautiful box and installed it ......, We are all decorator, and we are all modifying this person. How do you understand this?
Decoration mode: The decoration mode extends the object functions in a transparent way to the client. It is an alternative to the inheritance relationship and provides more flexibility than inheritance. Dynamically adds features to an object, which can be dynamically revoked. A large number of functions are generated by the arrangement and combination of some basic functions.
10. Facade-I have a professional Nikon camera. I like to adjust the aperture and shutter manually. In this way, only the photos I have taken are professional, but mm doesn't understand this. It won't take me a long time to teach. Fortunately, the camera has a facade design mode, which allows you to adjust the camera to the automatic file. You only need to aim at the target and press the shutter. Everything is automatically adjusted by the camera, in this way, mm can also use this camera to take a photo for me.
Facade mode: external communication with a sub-system must be performed through a unified facade object. The facade mode provides a high-level interface to make subsystems easier to use. Each subsystem has only one portal class, and this portal class has only one instance, that is, it is a singleton mode. However, the entire system can have multiple portals.
11. flyweight-I send text messages to mm every day, and my fingers are exhausted. I recently bought a new mobile phone. I can put some commonly used sentences into my mobile phone. I can take them out directly when I use them, add the MM name to the front and you will be able to send the message without a single word. The shared sentence is flyweight, And the MM name is the extracted external feature, which is used according to the context.
Enjoy mode: flyweight is the most lightweight in boxing. The metadata mode efficiently supports a large number of fine-grained objects in a shared manner. The key to the sharing mode is to distinguish between the internal and external states. The internal status is stored in the shared element and will not change with the environment. The external state changes with the change of the environment. The external status cannot affect the internal status. They are independent of each other. The States that can be shared and those that cannot be shared are separated from the conventional classes to remove the States that cannot be shared from the classes. The client cannot directly create shared objects, but should use a factory object to create shared objects. The metadata mode greatly reduces the number of objects in the memory.
12. Proxy-chatting with mm on the Internet always starts with "hi, hello". "Where are you from ?" "How old are you ?" "How tall ?" These words are really annoying. Write a program as my proxy. When I receive these words, I have set up an automatic answer. When I receive other words, I will be notified of the answer, cool.
Proxy mode: the proxy mode provides a proxy object for an object and controls the reference to the source object. An agent is an action taken by one person or institution on behalf of another person or institution. In some cases, the customer does not want or cannot directly reference an object. The proxy object can serve as an intermediary between the customer and the target object. The client cannot identify the proxy topic object and the real topic object. The proxy mode does not know the real proxy object, but only holds an interface of the proxy object. At this time, the proxy object cannot be created as the proxy object, the proxy object must have other roles created and passed in on behalf of the system.
13. Chain of responsibleity-I went to the English class at night and sat down in the last row for good convenience. Wow, I sat in front of several beautiful mm. I found a piece of paper and wrote "Hi, can I be my girlfriend? If you don't want to, please pass it to the front. The paper is uploaded one by one. Unfortunately, the mm in the first row passed the paper to the teacher. I heard it was an old virgin. Run fast!
Responsibility Chain Mode: In the responsibility chain mode, many objects are referenced by each object to its next home.
To form a chain. Requests are transmitted on this chain until an object on the chain decides to process this request. The customer does not know which object on the chain finally processes this request. The system can dynamically reorganize the chain and assign responsibility without affecting the client. The handler has two options: Take responsibility or push the responsibility to the next house. A request cannot be accepted by any receiving end object.
14. Command-I have a mm family with very strict management and can't meet each other. I had to use her brother to send messages between us. What instructions does she give me, write a piece of paper for her brother to bring to me. No, her brother sent another command. To thank him, I asked him to eat a bowl of soy sauce. He said, "I also sent command to my sister and three boyfriends, you are the least angry to ask me to eat noodles. ", :-(
Command mode: The command mode encapsulates a request or operation into an object. The command mode separates the responsibility for issuing commands from the responsibility for executing commands and delegates them to different objects. In command mode, the requester and the sender are allowed to be independent, so that the requester does not have to know the interfaces of the receiver, how the request is received, and whether the operation is executed, when and how it is executed. The system supports command revocation.
15. interpreter-I have a "bubble mm Sutra" with various tips on bubble mm, such as the steps to eat western food and the methods to watch movies. When I am dating mm, you only need to create an interpreter and execute it according to the above script.
Interpreter mode: Given a language, the interpreter mode can define a representation of its syntax and provide an interpreter at the same time. The client can use this interpreter to explain sentences in this language. The interpreter mode describes how to explain these statements with a simple syntax. The language mentioned in the interpreter mode refers to any combination that any interpreter object can interpret. In the interpreter mode, you need to define a hierarchical structure of a command class that represents grammar, that is, a series of combination rules. Each command object has an interpretation method, which represents an interpretation of the command object. Any permutation and combination of objects in the hierarchical structure of command objects is a language.
16. iterator-I fell in love with Mary and proposed to her desperately.
Mary: "If I want to marry you, I have to agree to my conditions"
Me: "I agree with all the conditions. Let's talk about it"
Mary: "I saw the 1 karat diamond"
Me: "I bought, I bought, are there any other products ?"
Mary: "I saw the villa by the lake"
Me: "I bought, I bought, are there any other products ?"
Mary: "Your younger brother must be 50cm long"
I sat down in a chair and bit my teeth: "I cut, I cut, is there anything else ?"
Iteration sub-mode: the iteration sub-mode can sequentially access an element in the aggregation without exposing the internal representation of the aggregation. The aggregation of multiple objects is called aggregation. Clustering objects are container objects that can accommodate a group of objects. The iteration sub-mode encapsulates the iteration logic into an independent sub-object, which is separated from the aggregation itself. The iteration submode simplifies the aggregation interface. Each clustering object can have one or more iteration sub-objects. The iteration status of each iteration sub-object can be independent of each other. Iteration Algorithm It can be independent from the change of the clustered role.
17. The mediator-four mm players played mahjong. It was unclear who should pay for each other. Fortunately, I was there and counted the money based on my chips, if you make money, you can get it from me. If you lose the money, you can pay it to me. Everything is OK. You get a phone number of four mm.
Called by mode: The called by mode encapsulates a series of ways in which objects interact, so that these objects do not have to interact explicitly. So that they can be loosely coupled. When the roles of some objects change, the roles of other objects are not immediately affected. Ensure that these functions can be changed independently of each other. The mediator mode converts the multi-to-many interaction into one-to-many interaction. The mediation mode abstracts the behavior and collaboration of objects, and processes the interaction between objects and other objects on a small scale.
18. Memento-Remember what you said to mm when you chat with several mm at the same time, or mm will be unhappy if it finds out. Fortunately, I have a memorandum, I copied a copy of what I said to the mm and saved it in the memo so that I can view the previous records at any time.
Memorandum mode: A memorandum object is an object used to store snapshots of the internal state of another object. The purpose of the memorandum mode is to catch the state of an object without damaging the encapsulation, and store it externally, in this way, this object can be restored to the stored state when appropriate in the future.
19. Observer-do you want to know our company's latest mm intelligence? Join the company's mm intelligence contact list. Tom is responsible for collecting intelligence. The new intelligence he found does not need to notify us one by one and is directly released to the contact list. We serve as subscribers (observers) you can receive the information in time.
Observer mode: The Observer mode defines a multi-team dependency, allowing multiple observer objects to listen to a single topic object at the same time. When the status of this topic object changes, it notifies all observer objects so that they can automatically update themselves.
20. State-when interacting with MM, you must pay attention to her status. In different states, her behavior may be different. For example, if you ask her to go to a movie this evening, if mm is not interested in you, he will say "something is going on". If mm is not so annoying to you but doesn't like it, he will say "okay, but can I bring my colleagues? ", If you like your mm, you will say, "What time is it? How about watching a movie ?", Of course, if you are doing well during a movie, you can also turn the status of mm from dislike to liking.
State mode: State mode allows an object to change its behavior when its internal state changes. This object seems to have changed its class. The state pattern encapsulates the behavior of the studied object in different State objects. Each State object belongs to a subclass of an abstract state class. The intention of the state mode is to change the behavior of an object when its internal state changes. The State mode creates a subclass of the state class for the possible states of each system. When the system status changes, the system changes the selected subclass.
21. Strategy-for dates with different types of MM, different strategies should be used. Some movies are recommended, some are recommended for snacks, and some are recommended for romance at the seaside, the single goal is to get the attention of mm. There are a lot of strategy in my pursuit of mm.
Policy mode: the Policy mode encapsulates each algorithm into an independent class with a common interface for a group of algorithms so that they can be replaced with each other. The policy mode allows the algorithm to change without affecting the client. Rule mode separates behavior from environment. The environment class is responsible for maintaining and querying behavior classes, and various algorithms are provided in specific policy classes. Because the algorithm and environment are independent, the increase, decrease, and modification of the algorithm will not affect the environment and the client.
22. template method-read the classic "how to persuade girls to bed" Article ? From the process of realizing that a girl goes to bed, there are eight steps (Template Method): encounter, break the deadlock, pursue, kiss, foreplay, start-up, caress, and enter ), however, each step has a different approach for different situations. It depends on your response (specific implementation );
Template Method mode: The template method mode prepares an abstract class, implements part of the logic in the form of a specific method and a specific constructor, and then declares some abstract methods to force the subclass to implement the remaining logic. Different sub-classes can implement these abstract methods in different ways to implement the rest logic differently. First, create a top-level logic framework, and leave the logic details to specific sub-classes for implementation.
23. Visitor-when Valentine's Day is approaching, each mm will be given a bunch of flowers and a card, but the flowers sent by each mm will be tailored to her own characteristics, each card should also be selected based on my own characteristics. I should find out where I am, and ask the florist and the gift shop owner for a visitor so that the florist can select a bunch of flowers based on the characteristics of mm, let the gift shop owner select a card based on each person's characteristics, which makes it much easier;
Visitor mode: the visitor mode aims to encapsulate operations that are applied to certain data structure elements. Once these operations need to be modified, the data structure that accepts the operation can remain unchanged. The visitor mode is suitable for systems with relatively undetermined data structures. It frees the coupling between the data structure and the operations acting on the structure, allowing the operation set to evolve freely. The visitor mode makes it easy to add new operations, that is, to add a new visitor class. In the visitor mode, the related behaviors are concentrated in a visitor object, rather than scattered into node classes. When using the visitor mode, put as many object browsing logic as possible in the visitor class, rather than in its subclass. The visitor mode allows you to access member classes of different hierarchies over the hierarchical structure of several classes.