Design-Patterns | : key : Gof Design Patterns Implementation | Architecture library
kandi X-RAY | Design-Patterns Summary
kandi X-RAY | Design-Patterns Summary
代码基于《Head First 设计模式》与《设计模式: 可复用面向对象软件的基础》,尽量保证简单易懂。.
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Currently covering the most popular Java, JavaScript and Python libraries. See a Sample of Design-Patterns
Design-Patterns Key Features
Design-Patterns Examples and Code Snippets
@Slf4j
public abstract class StealingMethod {
protected abstract String pickTarget();
protected abstract void confuseTarget(String target);
protected abstract void stealTheItem(String target);
public void steal() {
var target = pickTa
Community Discussions
Trending Discussions on Design-Patterns
QUESTION
I'm new to OpenSearch, and I'm following the indexing pattern mentioned here for a POC.
I'm trying to test the mapping mentioned here : https://github.com/spryker/search/blob/master/src/Spryker/Shared/Search/IndexMap/search.json in OpenSearch dev console.
...ANSWER
Answered 2022-Mar-30 at 03:46You need to replace page
by _doc
(or remove it altogether) as there's no more mapping types
QUESTION
I know this is well trodden territory but I have a specific question... I promise.
Having spent very little time in the statically typed, object oriented world, I recently came across this design pattern while reading Crafting Interpreters. While I understand this pattern allows for extensible behavior (methods) on a set of well defined existing types (classes), I don't quite get the characterization of it as a solution to the double dispatch problem, at least not without some additional assumptions. I see it more as making a tradeoff to the expression problem, where you trade closed types for open methods.
In most of the examples I've seen, you end up with something like this (shamelessly stolen from the awesome Clojure Design Patterns)
...ANSWER
Answered 2022-Feb-23 at 19:13The comment from @user207421 is spot on. If a language does not natively support double dispatch, no design pattern can alter the language to make it so. A pattern merely provides an alternative which may solve some of the problems that double dispatch would be applied to in another language.
People learning the Visitor Pattern who already have an understanding of double dispatch may be assisted by explanations such as, "Visitor solves a similar set of problems to those solved by double dispatch". Unfortunately, that explanation is often reduced to, "Visitor implements double dispatch" which is not true.
The fact you've recognized this means you have a solid understanding of both concepts already.
QUESTION
I was learning about the Bridge Design pattern. To quote:
The Bridge pattern attempts to solve this problem by switching from inheritance to the object
composition
. …
And then, the following image is shown:
When people are talking about composition as an alternative for inheritance, do they refer to both aggregation and composition relationships? If not, what do they mean exactly?
I wonder this because the picture has an aggregation relationship between Color
and Shape
, not a composition one.
ANSWER
Answered 2022-Feb-03 at 13:37Normally, when people talk about using composition vs. inheritance, they are talking about alternative ways of solving the same problem. In both cases, a "base class" provides an implementation of an interface that you want to reuse in your "derived class"
When you implement this with inheritance, there is an undesirable is-a relationship between the derived class and the base class, with the effect that implementation details of the base class, which should be hidden, can become changes in the derived class class.
When you implement this with composition -- a real composition relationship -- the "derived" only has an is-a relationship with the interface that it wants to implement, and the cost of this is that it must delegate calls to the "base" class.
In the Bridge pattern, which you reference, the goal is a little different. You do want to isolate the containing class from change to the connected implementation, but there is no is-a relationship between the containing class and an interface of the contained class.
The relationship between them may be one of composition, or may be simple aggregation -- that is an implementation detail. Often, the concrete implementation of the contained class will be injected as an interface into the containing class constructor, and in that case the relationship is just aggregation.
QUESTION
as shown in the code below:
...ANSWER
Answered 2022-Jan-28 at 02:13You're using the wrong dynamic method. What you want is dynamicMemberLookup
. Watch closely. First, the preparation:
QUESTION
We are using the "auto delay until last" pattern from the docs, https://www.optaplanner.org/docs/optaplanner/latest/design-patterns/design-patterns.html
The loop detection computation is extremely expensive, and we would like to minimize the number of times it is called. Right now, it is being called in the @AfterVariableChanged
method of the arrival time shadow variable listener.
The only information I have available in that method is the stop that got a new previous stop and the score director. A move may change several planning variables, so I will be doing the loop detection once for every planning variable that changed, when I should only have to do it once per move (and possibly undo move, unless I can be really clever and cache the loop detection result across moves).
Is there a way for me, from the score director, to figure out what move is being executed right now? I have no need to know exactly what move or what kind of move is being performed, only whether I am still in the same move as before.
I tried using scoreDirector.toString()
, which has an incrementing number in it, but that number appears to be the same for a move and the corresponding undo move.
ANSWER
Answered 2021-Nov-29 at 09:25No, there is no access to a move from scoring code. That is by design - scoring needs to be independent of moves executed. Any solution has a score, and if two solutions represent the same state of the problem, their scores must equal - therefore the only thing that matters for the purposes of scoring is the state of the solution, not the state of the solver or any other external factor.
QUESTION
I have a question about new
and delete
:
Should I use delete
for the input parameter or member object, e.g.:
https://github.com/jwbecalm/Head-First-Design-Patterns-in-CPP/blob/main/ch01_Strategy/main.cpp
Should I use delete
on the object allocated by new FlyNewWay()
?
ANSWER
Answered 2021-Oct-20 at 07:00Yes whenever you use new
keyword to allocate some memory then you must always use delete
to free up that memory later when no longer needed. Otherwise you will have a memory leak as in your program. In your case you should use delete
inside the destructor in the MallarDuck.cpp .
Other solution would be to use smart pointers like unique_ptr
so that you don't have to explicitly free the memory.
unique_ptr`'s syntax would something like:
QUESTION
I find it difficult to learn both Design Pattern and UML since there are different ways to describe the same pattern which make me unsure what is the single source of truth.
Take Iterator pattern for example, here are just a few diagrams that I saw from well-known sites:
1 WIKIPEDIA
https://en.wikipedia.org/wiki/Iterator_pattern
2 TUTORIALS POINT
https://www.tutorialspoint.com/design_pattern/iterator_pattern.htm
3 REFACTORING GURU
https://refactoring.guru/design-patterns/iterator
4 OODESIGN
https://www.oodesign.com/iterator-pattern.html
5 HOWTODOINJAVA
https://howtodoinjava.com/design-patterns/behavioral/iterator-design-pattern/
What confuses me the most is how arrow symbols are used to describe the relationship between these classes. Sometimes they are generalization, sometimes interface realization, directed association or dependency. Even composition is also used...
I wonder what would be the best way for me to get my head around all this.
...ANSWER
Answered 2021-Aug-31 at 08:47In general, one needs to be very careful when looking at UML models for design patterns. There are three reasons:
- The reference for design patterns is the GoF. This book was published in 1995, before UML even existed, and used a variation of the OMT notation (an ancestor of UML). In case if doubts, this is the source to trust.
- The Java language design was made public in 1995, JDK 1.0 release in January 1996, and the language not yet widely known. The authors based their designs and code examples on a C++ class model, i.e. on classes and inheritance only, without bothering for multiple inheritance. Most modern languages do not support multiple inheritance. As a consequence, some of the original patterns have to be adapted for Java, C# or Swift, to make a distinction between classes, abstract classes and interfaces, and between inheritance and interface implementation. There are multiple ways to do this. For example, some systematically converted abstract classes to interfaces. Some converted them only when there was a conflict. And some converted according to the interface "spirit".
- Misunderstandings happen. Some people publish such diagrams on the net but misunderstand the pattern, or misunderstand UML, or both together. Also, Gamma et al started the book when they were PhD students and also made some mistakes. You'll find for example some inconcsitencies in their use of the OMT aggregation.
- The worst case is the Builder pattern, where you have not only those problems, but on top of that you have a naming conflict: a very popular Java book introduced a (very different) variant of the builder pattern, with a different intent and another design, which caused total confusion.
Now to your specific example, and based on the content you have provided:
- oodesign is the closest to the original pattern and fully accurate. Btw, I mostly use links to their pages when it comes to patterns.
- refactoring guru is also a good choice. They opted to use interfaces instead of abstract classes, which is fine. But they have redefined the interface's operations and properties (probably in relation to own examples) and require a bidirectional navigation that seems not justified. If you're interested, there is a "Head First: Design patterns" which uses a similar mapping but keeps the original interface.
- wikipedia is not bad either: they have left out the client (which the GoF showed in light gray, to suggest that it's not essential for this pattern); They are more precise and complete on dependencies; But they also redefined the operations and properties differently. And they added an unnecessary aggregation symbol.
- How to make it in Java is confusing, because they kept one abstract class and opted for an interface for the other. And they have hidden the operations and properties. But there's nothing fundamentally wrong at first sight.
- Forget about tutorial points, at least for this UML diagram. It's plain wrong, as @qwerty_so already mentioned in the comments.
The statement of accuracy is for this pattern only and for the current version of the content. This cannot be generalized to all the design patterns in view of my introductory remarks.
QUESTION
I need to run multiple async operations, until one of them returns a certain result - in other words, the "Chain of Responsibility" pattern.
When I tried to implement it, some
was the first thing that came up. However I'm having troubles with the asynchronous calls, as the loop gets "stuck" after the first iteration:
ANSWER
Answered 2021-Aug-11 at 19:40Here's an idea
QUESTION
This explains the "Bridge" pattern I'm referring to: https://refactoring.guru/design-patterns/bridge
Here's a scenario from the post above:
Say you have a geometric Shape class with a pair of subclasses: Circle and Square. You want to extend this class hierarchy to incorporate colors, so you plan to create Red and Blue shape subclasses. However, since you already have two subclasses, you’ll need to create four class combinations such as BlueCircle and RedSquare.
The problem this scenario presents:
Adding new shape types and colors to the hierarchy will grow it exponentially. For example, to add a triangle shape you’d need to introduce two subclasses, one for each color. And after that, adding a new color would require creating three subclasses, one for each shape type. The further we go, the worse it becomes.
To avoid this problem, we implement the Bridge pattern like so:
Extract the color-related code into its own class with two subclasses: Red and Blue. The Shape class then gets a reference field pointing to one of the color objects. Now the shape can delegate any color-related work to the linked color object. That reference will act as a bridge between the Shape and Color classes. From now on, adding new colors won’t require changing the shape hierarchy, and vice versa.
I understand the how and why of this implementation.
But what if we need a third hierarchy, e.g. BorderStyle
(where a border style can be Straight
, Wavy
, or ZigZag
?)
I guess we could implement a second Implementor class for BorderStyle
and pass it into a Shape
constructor like so:
ANSWER
Answered 2021-Jun-10 at 00:45Yes, this works. There's nothing wrong with adding two Bridge relationships to one abstraction (beyond the complexity of juggling three different hierarchies).
Decorator would certainly not work for this purpose, because it maintains a single hierarchy, which is known to the client. The Implementor
hierarchy in a Bridge (or hierarchies in this case) are unknown to the client.
I would make a clarification to the linked article, where it says,
You want to extend this [shape] class hierarchy to incorporate colors
I think this oversimplifies the motivation for a Bridge. The Implementor
s are not just some attributes you choose to add to your Abstraction
to enhance it. Your Abstraction
requires an Implementor
in order to function at all. The method implementations within subclasses of Abstraction
generally do little except call methods of the Implementor
.
The Abstraction
represents your high-level, business API, while the Implementor
represents a lower-level, primitive API. They are both abstractions, but at different levels. I don't think this is conveyed adequately by shape & color examples because shape and color seem like abstractions at the same level. Both shape and color would be known to the clients, and neither one strictly depends on the other.
So a Bridge is applied for more specific reasons than the given example, but you certainly can have two.
QUESTION
I am trying to organise my code into a more OOP style with each class taking on its own header and cpp file. This is my tree in the package folder in the workspace
...ANSWER
Answered 2021-Jun-09 at 02:37In essence you don't need to include either header into the other. This fixes the circular includes.
In ROS_Topic_Thread.h, friend class Master_Thread;
already forward declares Mater_Thread, so you don't need the Master_Thread.h header.
In Master_Thread.h, you can also forward declare class ROS_Topic_Thread;
before the declaration of the Master_Thread class, since you only use references to ROS_Topic_Thread in the transfer_to_master_buffer
method.
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