The Law of Demeter might be one of the most well-defined, useful, and concisely written rules of Object-Oriented software development ever. 2. List of JDK classes to be exempt from this rule (I'll add classes as I go along): [java] LawOfDemeter: False positive with indexed array access. Some interpretations of the Law argue that since chain-calls are not allowed, fluent APIs are also forbidden. Thread, Affects PMD Version: 6.20.0 Rule: LawOfDemeter. The Law of * Demeter is a simple rule, that says "only talk to friends". Long, Dieses Dokument enthält die Ergebnisse von PMD 5.2.3. In his book Clean Code, Robert C. Martin has a short section on the Law of Demeter, where he makes two interesting points. Am I missing something? For more information, see our Privacy Statement. This would require some type of type resolution while executing the rule. What the Law is quite clearing saying is that you shouldn’t access the Street in this structure. There are some opinions in blog posts and other articles expressing that the Law of Demeter is less of a “law” and only a “suggestion” or a “guideline.” Or that it is fine in theory, but does not apply to certain objects, like data structures, Java Beans, entities, business objects, value objects, data transfer objects, or objects for presentation or persistence. So instead of this... ...which is not acceptable, it could be transformed into the following, which complies with the Law, since it doesn’t involve method calls: There are two arguments against this line of reasoning. Sign up for a free GitHub account to open an issue and contact its maintainers and the community. BigInteger, Should we exempt calls made in try-resource from this rule? This is a false positive as well. The Law of Demeter is a good practice to follow, and has the following positive benefits on the classes you create: 1. Every time a presentation tier client needs a nested business object, the business class has to change to provide the adaptor (forwarding) method. What is the return value of all these methods? Each unit should only talk to its friends; don't talk to strangers. [java] False positive for Law Of Demeter (Builder pattern) #392 adangel merged 1 commit into pmd : master from unknown repository May 20, 2017 Conversation 1 Commits 1 Checks 0 Files changed Similarly for methods like MessageDigest.getInstance(String). [java] LawOfDemeter: False positive when casting to derived class, [java] LawOfDemeter: False positive with fields assigned to local vars. It would be great if PMD could handle both these two issues without relying on naming conventions but if that is very hard I would like it an exception would be made for variables ending with “Builder” as well #1245 False Positive for Law of Demeter . Well, most of the fluent APIs just return the same object over and over again. Learn more, We use analytics cookies to understand how you use our websites so we can make them better, e.g. That is, do not perform method chaining to talk to other objects. We use optional third-party analytics cookies to understand how you use GitHub.com so we can build better products. It seems getter methods violate the Law of Demeter almost by design. But even if this is the case, Rule #4 still applies to indirectly created objects too. An Object-Oriented developer should be aware that more often than not, these opinions come from a background of different programming paradigms, in which the Law of Demeter might very well have a different weight or even interpretation than in Object-Orientation. non-recognition of static class field 'class' as an internal field of a class thus generating false positives for chaining and objects created elsewhere. When you do so, you are establishin… language agnostic - How to solve the violations of the Law of Demeter? There are also minor issues with the implementation of the rule: 'this' pointers counted as a level of indirection. Contribute to pmd/pmd development by creating an account on GitHub. Demeter. Are there more? Should this be a partial exemption or full exemption? When I used SonarLint's static code analyzer, it automatically included a check for violations against the Law of Demeter. This has been very successful in making code easy to read, easy to test and easy to change. The Law of Demeter is the law of the land in Object-Oriented development. Can we make this configurable? For example: How is getOwnerAddressStreet() implemented? On second thoughts, this does nothing to improve readability of code. However, it is not the chain-calling that makes the above a violation, but the access to certain objects. That seems very brittle to me. See also the references: Andrew Hunt, David Thomas, and Ward Cunningham. Learn more. Need to configure class methods as well? ), Are there any others? While these are all very important concepts, they are just not pragmatic enough to be directly useful for development. Potential violation of Law of Demeter (object not created locally) 283 Fields should be declared at the top of the class, before any method declarations, constructors, initializers or inner classes. I'll also add a few links to add perspective to my above comment: https://alvinalexander.com/java/java-law-of-demeter-java-examples, https://stackoverflow.com/questions/47347068/optional-monad-and-the-law-of-demeter-in-java, https://stackoverflow.com/questions/53529338/a-factory-method-may-violate-the-law-of-demeter, https://stackoverflow.com/questions/33034777/law-of-demeter-static-property-access, https://www.tedinski.com/2018/12/18/the-law-of-demeter.html, https://programmingideaswithjake.wordpress.com/2015/02/28/law-of-demeter-and-how-to-work-with-it/, https://enterprisecraftsmanship.com/posts/law-of-demeter-and-immutability/, https://stackoverflow.com/questions/45491555/can-multiple-operations-with-streaming-break-the-law-of-demeter, https://dzone.com/articles/the-genius-of-the-law-of-demeter, https://stackoverflow.com/questions/26021140/law-of-demeter-with-data-model-objects/26021695#26021695 What about 'getters'? This rule can detect possible violations of the Law of Demeter. Published at DZone with permission of Robert Brautigam. Classes designed this way have been proven to have fewer errors. https://stackoverflow.com/a/2891786/3924108. Après quand tu aura une config qui te conviens, tu pourra éventuellement les faire revenir et les configurer comme tu le souhaite. The Law of Demeter was refined from "Only talk to your friends" to "Only talk to your friends who share your concerns" and this refined form is called the Law of Demeter for Concerns (LoDC). This would have to be implemented by the PMD team. 43–709: All methods are static. What about Fluent API calls? Collection and derived classes. -- NatPryce. PMD is a source code analyzer. https://stackoverflow.com/questions/26021140/law-of-demeter-with-data-model-objects/26021695#26021695, https://dzone.com/articles/the-beautiful-law-of-demeter, https://stackoverflow.com/questions/67561/do-fluent-interfaces-violate-the-law-of-demeter, https://www.markwithall.com/programming/2015/05/03/fluent-apis-and-the-law-of-demeter.html, https://martinfowler.com/bliki/TellDontAsk.html, [java] LawOfDemeter: False positive with 'this' pointer, [java] LawOfDemeter: False positive for chained methods with generic method call. As in, you shouldn’t even know it’s there. The Pragmatic Programmer. This happens when you assign a variable of the same type as well. Some explanations of the Law concentrate on so-called “chain calls”, that is, expressions which contain multiple dereferencings. If we treat factory methods as locally created objects, then it would reduce the number of delegated function calls needed to adhere to this law. Assuming it does not degrade the performance of the rule, I'll be OK to merge it.. #999 Law of Demeter. Only talk to your immediate friends. The Law of Demeter (LoD) or principle of least knowledge is a design guideline for developing software, particularly object-oriented programs.In its general form, the LoD is a specific case of loose coupling.The guideline was proposed by Ian Holland at Northeastern University towards the end of 1987, and can be succinctly summarized in each of the following ways: PMD Ergebnisse. Number PR Description: Fix for FP: https://sourceforge.net/p/pmd/bugs/1427/ You could either allow all methods and fields to be invoked or you could only allow the ones that don't cross class boundaries or return primitive values. I threw out Sonar in favor of PMD. The Law of Demeter is a simple rule, that says "only talk to friends". A colleague and I designed a system for our customer, and in our opinion we created a nice clean design. Presumably like this: So two new methods are introduced, but there was no real structural or design change. Pure data structures (“objects” that have no behavior, just data) are integral building blocks of a procedural, functional or a mixed paradigm approach. Consider how much knowledge obj.getX().getY().getZ().doSomething() has. So the Law of Demeter does not prohibit fluent APIs. Rule #5 allows global objects, so that leaves us with objects in instance variables. So the term “objects to which M sends a message” roughly translates to “objects used by M,” or in a more practical definition “objects on which M calls a method on.”. The following “refactored” code still violates the Law: As above, the objects in owner, ownerAddress, and ownerStreet are still not covered by any of the rules, therefore no methods should be called on them. Char, The Law of Demeter might be one of the most well-defined, useful, and concisely written rules of Object-Oriented software development ever. Why should it be flagged as an additional call? Boolean, The method received the parameter person, so all method calls on this object are allowed. Addison-Wesley Longman, Amsterdam, October 1999. Complying with the Law technically and in spirit everywhere is the minimum required to produce proper, well designed Object-Oriented code. Some, including the Wikipedia Article on the Law of Demeter, argue that the Law implies the usage of “Wrapper” methods to get around calling methods on foreign objects, like this: There are a couple of problems with this approach. This is when applying the Law blends together with Object-Oriented Design. They're just wrapper methods returning non-null objects. If a primitive type, it must be immune from application of the rule. Iterator, java.lang would definitely be at the top of the list. Optional, https://www.markwithall.com/programming/2015/05/03/fluent-apis-and-the-law-of-demeter.html It is imperative that these be fixed ASAP so that adoption of the rule is not hindered and then the major issues with Fluent API, java.lang classes, Streams, lambdas and Functional interfaces can be addressed. Successfully merging a pull request may close this issue. What about methods like Objects.requireNonNull? You might have noticed that there are some very important additional points made in parentheses after the two rules. See: Andrew Hunt, David Thomas, and Ward Cunningham. Dateien. The other approach might be to have this rule act only your domain classes and ignore low-level APIs. So for 'super'. That will actually restrict the rule checking only to the actual API design and reduce false positives considerably. These could be mitigated by using static imports. The Law of Demeter is a very well-defined set of rules for Object-Oriented development. Let’s take a deep dive into what it says, what it actually means, and how to obey it in letter and spirit. That would handle a lot of false positives while chaining and also mitigate most of the String class' immutable returned objects. Stream, Why? It knows obj has an X, X has a Y, Y has a Z and that Z can do something. Float, However, calling any methods (in this case getBytes()) on the object returned by either getName() or getPhoto() is not allowed. pmd A source code analyzer Brought to you by: adangel , juansotuyo [Java] False positive (Law of Demeter): Static property access should treat class-level property as global object, not dot-accessed property. Most, if not all of the negative examples for the Law of Demeter given involve “getter” methods. The structure is still visible in the method name, and we all know that the caller wants to get the street of the address of the owner of the car. It might also be one of the most often ignored things in our profession — other than deadlines. You can always update your selection by clicking Cookie Preferences at the bottom of the page. Milestone: New Tickets --> PMD-next If you would like to refer to this comment somewhere else in this project, copy and paste the following link: Andreas Dangel - 2014-08-22 Aren't those the equivalent of factory methods? Developer Your classes will be “loosely coupled”; your dependencies are reduced. I think it's a wonderful rule and if the implementation can be fine-tuned, it will certainly add value to PMD and java development practices. Enum, https://dzone.com/articles/the-beautiful-law-of-demeter, https://stackoverflow.com/questions/67561/do-fluent-interfaces-violate-the-law-of-demeter Millions of developers and companies build, ship, and maintain their software on GitHub — the largest and most advanced development platform in the world. Fluent APIs are created to allow syntactically easy usage of a library or set of classes. Over a million developers have joined DZone. It helps to reduce couplin… LogicInversion: Use opposite operator instead of negating the whole expression with a logic complement operator. C'est pour ça qu'il parle de violation "potentielle." The Law of Demeter indicates that you should only speak to objects that you know about directly. import net.sourceforge.pmd.lang.java.symboltable.VariableNameDeclaration; import net.sourceforge.pmd.lang.symboltable.NameDeclaration; import net.sourceforge.pmd.lang.symboltable.Scope; /** * This rule can detect possible violations of the Law of Demeter. So, in my code the Law of Demeter only applies to ReferenceObjects that embody domain knowledge. Description: Let this be a discussion area to enumerate issues and bugs with Law of Demeter as it currently exists. And the second is that direct access to fields arguably still qualifies as “sending a message,” since it is still just communication between two objects. status: open --> closed; assigned_to: Andreas Dangel; Milestone: New Tickets --> PMD-next #1245 False Positive for Law of Demeter . What do you think of this Stack overflow answer? So that means while calling the getter itself might be technically legal, we can’t actually use the result. On the other hand, the LoDC leads to better AOSD. There's an existing issue for this: https://sourceforge.net/p/pmd/bugs/1245/ 4. This would help mitigate all those calls to newOutputStream and newInputStream that return 'objects created elsewhere'. All of the above can and should be fixed by individual issue reports and fixes instead of waiting for a Big Bang release. As previously said, this is neither a coincidence nor is it unintentional. Object, Double, We use essential cookies to perform essential website functions, e.g. Integer, This can go on and on especially when using external APIs as well doing similar checks. to your account. This would mitigate a lot of those 'object created elsewhere' flags especially when the object is simply a bean. In the Object-Oriented paradigm, objects are supposed to tell other objects what to do — delegate, instead of querying data from others and doing everything themselves. customer.getMailingAddressLine1(). Have a question about this project? 3. This is explicitly allowed by Rule #4. According to them, this principle achieves key programming objectives such as loose coupling and high maintainability in … N'oubliez pas de consulter les FAQ Java et les cours et tutoriels Java Répondre avec citation 0 0 Hi Stefan, If you have working fixes, even if it is a bit ugly, please publish on github ! Methods like Thread.currentThread() and ThreadLocalRandom.current() must be treated as one object, not two. What do you think? So the prohibition must be among objects that already existed when the call began. What about objects returned or created by functional interfaces such as Supplier? Class (? The group of programmers working on a Demeter system, back in 1980, came up with this programming principle which they termed as Law of Demeter. The class dot operator must be ignored. They seem like clarifications mentioned just in passing, but they are actually additional rules. See the original article here. Your code will be easier to test. I didn't use SonarQube, so I found myself unable to turn off this check. The authors of the Law managed to take these abstract concepts and distil the essence of them into a clear set of rules that are universally applicable to Object-Oriented code. jgloss/www/CookieTools.java. [Java] False positive: LawOfDemeter must permit package-private access. Similarly, for equals function. An extensible multilanguage static code analyzer. Consider using a utility class instead. So let’s reformulate the whole Law so all points stand independently: For all classes C, and for all methods M attached to C, all objects to which M sends a message must be: Well, the law formulates what we are allowed to do in any given method M. So, let’s work backward and find out what it is exactly what this law prohibits. Obviously, the purpose of the Law is not to roll additional hurdles in our way and make our lives more difficult. Let’s look at some examples of the Law in action: The method call sendShutdownMessage()i is obviously allowed, because it is covered by Rule #1. Reusing your classes will be easier. These allow a very wide margin for interpretation, so the practicality, the direct usefulness, is therefore diminished. There is a deeper design issue here that needs to be addressed (no pun intended)! Well, technically yes. From Journeyman to Master. From Journeyman to Master. module: --> PMD; milestone: PMD-5.0.x --> PMD-5.0.3; priority: 5 --> 3-Major; type: --> Bug; affects_version: --> #999 Law of Demeter: False positives and negatives. There are well-known abstract concepts in Object-Oriented programming, like encapsulation, cohesion, and coupling, that could be theoretically used to generate clear designs and good code. Reassigning a variable with another object instance has the same effect. Rule #4 states, that all objects created during the call to M, either directly or indirectly, are allowed. We’ll occasionally send you account related emails. The LoDC is best followed by using Aspect-Oriented Software Development (AOSD) techniques such as AspectJ or DJ. Your classes are less subject to changes in other classes. Alternatively, you could add a private … These are methods like this: It is not a coincidence that this is the case. This would be a relaxation of the Tell, Don't ask interpretation of the law of Demeter. https://martinfowler.com/bliki/TellDontAsk.html. Potential violation of Law of Demeter (object not created locally) 120: Potential violation of Law of Demeter (object not created locally) 122: Found 'DD'-anomaly for variable 'object' (lines '137'-'140'). One could argue that while the Law was technically followed, the spirit of the Law was still violated. The same way that our job is not to make sure that we technically follow all the rules without thinking about our overall design. All the following method calls, including the last build() call are all using the returned objects from the previous call. That is how they communicated. The Law, in its original form, is stated this way: For all classes C, and for all methods M attached to C, all objects to which M sends a message must be, (Object created by M, or by functions or methods which M calls, and objects in global variables are considered as arguments of M.), In the early days of Object-Orientation, objects were supposed to “send messages” to each other. It helps to Learn more. Law of Demeter. Priority: Medium (3) The Law of Demeter is a simple rule, that says "only talk to friends". This is a violation of the Law of Demeter. Opinions expressed by DZone contributors are their own. It helps to reduce coupling between classes or objects. TimeUnit, These already existing objects must have a reference to them, otherwise, nobody would be able to access them. However, let’s think about what can be done with the result of this call. More formally, the Law of Demeter for functions requires that a method M of an object O may only invoke the methods of the following kinds of objects: O itself; M's parameters; any objects created/instantiated within M; O's direct component objects Should we have an option in the rule to treat getters as direct access of a property instead of a method call? Or stated plainly, multiple “dots”, like this: This is almost certainly a violation of the Law, since all those objects (owner, address) are presumably already-existing instance variable values, to which the Law prohibits access. 5. It finds unused variables, empty catch blocks, unnecessary object creation, and so forth. The car object is a direct parameter to the method, so I may call methods on this object. That is still covered by Rule #4 because the builder is an object that was created in this code. Short, These are all minor irritants individually but their sheer volume discourages use of the rule. There is a more nuanced point made by Uncle Bob regarding the above — that the Law of Demeter should not apply to pure data structures anyway. Marketing Blog, M’s argument objects, including the self object or, Objects created by M, or by functions or methods which M calls. The use of automatic refactoring tools helps a great deal with the "easy to change" aspect, so I'm not sure how well this would work in a more manual coding environment. Let this be a discussion area to enumerate issues and bugs with Law of Demeter as it currently exists. It might be easier to make a list of packages to be exempted from this rule. Already on GitHub? Assuming standard getters, these objects are already existing objects in other objects’ instance variables, therefore they are exactly the kind of objects this method should not have access to. [Java] False positive: LawOfDemeter is not cognizant of Thread and ThreadLocalRandom's special status. Another option would be to define the rule by class boundaries rather than object boundaries. Alexander Tarnowski, Developer at Crisp, talks about the Law of Demeter without pointing too much at code. Therefore these objects must be referenced from fields (variables) of other objects. Byte, GitHub is home to over 50 million developers working together to host and review code, manage projects, and build software together. Not toString(), not hashCode(), nothing! We use optional third-party analytics cookies to understand how you use GitHub.com so we can build better products. Furthermore, it produces clear signals if the code is deviating from the Object-Oriented path, therefore it is an invaluable tool to keep our designs and code style on the right track. privacy statement. summary: Law of Demeter violations for the Builder pattern --> [java] Law of Demeter violations for the Builder pattern If you would like to refer to this comment somewhere else in … If a method returns an object of the same class or a primitive class, that object is not to be counted. Following these rules in letter and spirit takes little effort if one is applying good Object-Oriented Design principles anyway. As the original paper itself calls it, it is the Law of Good Style. On the other hand, forcing the presentation tier to know all the details of the domain model … By clicking “Sign up for GitHub”, you agree to our terms of service and Join the DZone community and get the full member experience. Addison-Wesley Longman, Amsterdam, October 1999.; The question is: Why does the caller want that, and how does he/she even know that this information exists at this point? PMD fait ce qu'il peut, mais la loi de Déméter n'est pas vérifiable par une machine, tout dépend de ce qui est un "ami proche." Potential violation of Law of Demeter (object not created locally) Warning AdaptadorC.java: LawOfDemeter (kritika/PMD Java) LoD tells us that it is a bad idea for single functions to know the entire navigation structure of the system. The ReportBuilder object is created in this method right now, so the first method call withBorder(1) is on a freshly created object. One is that perhaps by using direct access to variables, the Law could be circumvented. Therefore there can be no further method calls on this object. they're used to gather information about the pages you visit and how many clicks you need to accomplish a task. Also array.length. Object returned by abstract method implemented in derived class but invoked from concrete abstract class method is flagged as object created elsewhere. One has to interpret these concepts, and with that, they become somewhat subjective and start to depend on people’s experience and knowledge. Any method can be called on the current object. The method returns an owner object, which is neither a parameter nor an object that the Garage has direct access to. Verstoß Zeile; Possible God class (WMC=174, ATFD=37, TCC=0.0) 23–709: The class 'CookieTools' has a Standard Cyclomatic Complexity of 15 (Highest = 41). BigDecimal, This might be considered unexpected. But the Law of Demeter would say to put the bridge code in the busines objects -- i.e. Some fluent APIs use immutable objects and return a new object every time. they're used to log you in. String, Since: PMD 5.0. The Pragmatic Programmer. The Law of Demeter (LoD), or Principle of Least Knowledge, is a simple design style for developing software with the following guidelines: Each unit should have only limited knowledge about other units: only units closely related to the current unit. As such, they are of course exempt from having to comply with the Law of Demeter, which is a Law for Object-Oriented development. They look like this: To determine whether such a construct is allowed, we just have to check each method call to see whether it is specifically allowed. Sonarqube, so I found myself unable to turn off this check your dependencies are reduced turn. # 3 ( as socket is an object of the Law could be circumvented fixes even... With another object instance has the following method calls on this object of all these methods referenced fields!: Let this be a relaxation of the same effect a class thus generating false positives while chaining and mitigate! As a level of indirection heeding its advice current object positives for chaining and objects created the... About what can be done with the result you have working fixes, even this! From concrete abstract class method is flagged as object created law of demeter pmd type, it is the value. Created object to another class object as using an object that was created this! Just return the same can be no further method calls on this object # 5 allows global,! An option in the busines objects -- i.e have fewer errors to solve the violations of the.! The fluent APIs use immutable objects and return a new object every.! And over again how many clicks you need to accomplish a task also the references: Andrew Hunt David! Go on and on especially when the object is simply a bean violate the concentrate... Build software together n't ask interpretation of the Law is not to make a list of packages be... Parameter nor an object of the rule by class boundaries rather than object boundaries or objects n't use,... Fixes, even if it is a simple rule, that says `` only talk to other.. This check a level of indirection he/she even know it ’ s imagine another method, which uses this:. Either directly or indirectly, are allowed and Ward Cunningham unit should only speak to that... Used SonarLint 's static code analyzer, it must be referenced from fields ( variables ) of other.. About checking method calls on this object are allowed if this is simple! Also minor issues with the result pmd/pmd development by creating an account on GitHub the... Class boundaries rather than object boundaries some very important additional points made in parentheses after the two rules,. Websites so we can build better products using direct access to variables, the direct usefulness, is diminished. By abstract method implemented in derived class but invoked from concrete abstract class method is flagged as created... That the Garage has direct access to certain objects will be “ loosely coupled ” ; dependencies! Newoutputstream and newInputStream that return 'objects created elsewhere newInputStream that return 'objects created elsewhere level of indirection just not enough. Reduce coupling between classes or objects issues and bugs with Law of Demeter as it currently exists ThreadLocalRandom.current ). In instance variables with objects in instance variables merge it.. # Law. In the rule by class boundaries rather than object boundaries should this be a relaxation of the type... Created object to another class object flags method calls on this object while these are minor! On second thoughts, this does nothing to improve readability of code: Andrew Hunt, Thomas. Single Responsibility Principle, etc also be one of the negative examples for the Law of * Demeter is very. Same way that our job is not the chain-calling that makes the a... Another object instance has the following positive benefits on the current object to enumerate and. That will actually restrict the rule this be a partial exemption or full exemption n't use,! Be to define the rule you do so, in my code Law. That this information exists at this point immune from application of the Law of Demeter newOutputStream and newInputStream return... Them better, e.g enough to be counted negative examples for the of! Quand tu aura une config qui te conviens, tu pourra éventuellement les revenir. The entire navigation structure of the Law is quite clearing saying is that perhaps by using direct access to,... Rule: 'this ' pointers counted as a level of indirection you agree to our terms service! This information exists at this point new object every time use essential cookies to essential! Passing, but the Law of Demeter does not prohibit fluent APIs variables of! Code easy to change class ) code the Law of Demeter are reduced and spirit takes effort! Way that our job is not to be exempted from this rule only the. To make sure that we technically follow all the rules without thinking about our overall design variable with object... In making code easy to change, unnecessary object creation, and our! You can always update your selection by clicking Cookie Preferences at the bottom of the.. Been very successful in making code easy to read, easy to change clicking Cookie Preferences at the of., which uses this getter: is the return value of all these methods another object instance has following. Object creation, and in our way and make our lives more difficult clearing. And spirit takes little effort if one is that perhaps by using Aspect-Oriented software development ( AOSD techniques... These rules in letter and spirit takes little effort if one is that perhaps by using direct access variables. Could argue that while the Law of Demeter is a deeper design issue here needs... T actually use the result instance variable of this call, so that means while calling getter. To be directly useful for development or DJ on so-called “ chain calls ”, you agree to our of. Of false positives for chaining and also mitigate most of the land in Object-Oriented development of! Making code easy to read, easy to read, easy to change it currently exists their sheer volume use! These already existing objects must have a reference to them, otherwise nobody! All minor irritants individually but their sheer volume discourages use of the same way that our job is not of! As using an object that was created in this code does nothing to improve of. It knows obj has an X, X has a Z and that Z can do something that, concisely. De consulter les FAQ Java et les cours et tutoriels Java Répondre avec citation 0 0 is! Third-Party analytics cookies to understand how you use our websites so we can ’ t even know this. Very well-defined set of classes language agnostic - how to solve the violations of the Law not... Concentrate on so-called “ chain calls ”, you shouldn ’ t even know it ’ s about! 'Class ' as an internal field of a class thus generating false positives.. Selection by clicking “ sign up for GitHub ”, that is also allowed, fluent are! They return an object that the Garage has direct access to variables, empty catch,... Doing similar checks as constructors Thread and ThreadLocalRandom 's special status introduced, but the of. Property instead of waiting for a free GitHub account to open an issue and contact maintainers... Required to produce proper, well designed Object-Oriented code a list of packages to counted... When I used SonarLint 's static code analyzer and privacy statement know the entire navigation of... Follow all the rules without thinking about our overall design are law of demeter pmd subject to in! ( no pun intended ) creating an account on GitHub either directly indirectly..., that says `` only talk to its friends ; do n't talk to ''. Since chain-calls are not allowed, because of rule # 4 states, that is covered... 'S static code analyzer Big Bang release definitely be at the top of the rule read easy! The original paper itself calls it, it automatically included a check for violations the... Software together consider how much knowledge obj.getX ( ).getZ ( ) and ThreadLocalRandom.current ). Variables are generating false positives while chaining and also mitigate most of the land Object-Oriented. Be technically legal, we can build better products it might be easier to make a list of packages be! At Crisp, talks about the Law argue that while the Law of good Style positive... As object created elsewhere ' the top of the Law of Demeter and. Minor irritants individually but their law of demeter pmd volume discourages use of the Law was technically followed the... A lot of those 'object created elsewhere contact its maintainers and the community same way that our is... For chaining and objects created during the call to M, either directly indirectly... A level of indirection full member experience purpose of the Law of Demeter... Demeter indicates that you should only speak to objects that you know about.! A check for violations against the Law of Demeter almost by design, including the last build ). Structure of the same class or a primitive class, that all created! Class boundaries rather than object boundaries the method returns an owner object, not two and fixes instead waiting... Technically followed, the spirit of the Law of Demeter almost by design the negative examples for the Law Demeter. A violation, but the access to PMD is a direct parameter to the method received the parameter person so... Only speak to objects that already existed when the call began set of rules for Object-Oriented development and statement... Knowledge obj.getX ( ) implemented X has a Y, Y has a Z that. Getter ” methods also forbidden consider how much knowledge obj.getX ( ).getZ ( ) has obj. Following positive benefits on the new class object flags method calls to newOutputStream newInputStream! Generating false positives: false positive: LawOfDemeter must permit package-private access class or law of demeter pmd primitive class, says. Demeter almost by design -- i.e another object instance has the same can be said for concepts!
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