Software design law of demeter example

In short, the law of demeter aims to keep away from doing things like this and try to make it simpler like this. Design and implement api based on the best practices developed by. The law of demeter for functions or methods, in java attempts to. See how the law of demeter stacks up with getters, chain calls, and other common tools.

It knows obj has an x, x has a y, y has a z and that z can do something. It is a software design guideline specially related to loose coupling. The law of demeter helps you apply the rules of object oriented programming for reusable, loosely coupled code a scalable and maintainable application. First discussed at the northeastern university in 1987, this principle states. The law of demeter is discussed using java source code examples. The law of demeter is also know as the principle of least knowledge.

So if somethings going to change, then something should be encapsulated. Demystifying the law of demeter principle infoworld. They all explain what it is and show an example of breaking the law but that is easy. It was designed to promote loose coupling in software designs. Here you can see, while we are getting the value of primaryemailaddress and mobile, lod is getting violated. There is probably lots of ways to obey this law good design and planning being one but in very simple terms would this be a way to obey it. Lod tells us that it is a bad idea for single functions to know the entire navigation structure of the system. Of software design, the law of demeter and credit card companies posted by. One of my favorite design patterns, and also, it respects the law.

Of software design, the law of demeter and credit card. Lawofdemeter dictionary definition lawofdemeter defined. E the following code show an example in which demeters law is violated. For example, the following code shows an example in which demeters law is.

For example, we discussed yesterday how to introduce a set of mock objects into a software system by simply switching factories using the abstract factory design pattern. Apache jmeter is opensource software, a 100% pure java application. Whenever you talk to a good, experienced programmer, they will tell you that loosely coupled classes are important to good software design. Software programming is a balanced mix of art sometimes a euphemism for improvisation and a bunch of. The law of demeter lod or principle of least knowledge is a design. The law of demeter is or might be in some designs related to the. 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. Lets understand the law of demeter with an example. The law of demeter lod or principle of least knowledge is a design guideline for developing software, particularly objectoriented programs. The law of demeter might be one of the most welldefined, useful, and concisely written rules of objectoriented software development ever. For a good software design, it is very important to have loosely. So lets see some code of example in java to explain law of demeter. The law of demeter helps you apply the rules of object oriented programming. In its general form, the lod is a specific case of loose coupling.

The design challenge is to know what could change and encapsulate that. The law of demeter or the principle of least knowledge is a design guideline for developing software applications. Each unit should have only limited knowledge about other units. Violation of law of demeter free video tutorial udemy.