Skip to main content

UML

how objects are connected, how they react/communicate.
Visualize and design
UML used to visualize the design
  • Associations simply show that there are some relationships between entities,static relation. ex: department offer courses.
    • 0..* zero or more (on both sides "many to many" )
    • 0..1 zero or one (one to one)
    • 1..* one or more (one to many)
  • Aggregation "has a" more specific than association "an association that represents (a whole part/ part) of a relation ship". ex: when a class is a collection/container of another class but the contained class doesn't have strong dependency on the container "if container destroyed, contents don't" (class container, students contained)
  • Composition "Owns"  more specific than aggregation, a strong life cycle dependency between instance of the container class and the contained, if container is destroyed, normally every instance that it contains is destroyed (school container, classes contained).
  • Generalization "Is a" (extends) solid.
  • Realization "one model implements the behavior of the other" dashed.
i.e:
relationship between entities have to be abstract so that unnecessary details doesn't hide the relationships between them 

Comments

Popular posts from this blog

The post-office & the postman

If we were to talk about old messaging system where there exist post-office, postman & mailbox. each component had its own functionality that we looked for when trying to visualize how those component where to interact in a computerized version. Simple scenario: Mail is added in mail box Postman arrive pick mails from his area mailboxes and take them to the post-office. Post-office organize mails by areas. Postman takes mails related to his area "distribute it in mailboxes". A person can go to post-office and  pick his own mail "in case of failure or wishes for early delivery". Mapping in a computerized version: Scenario: Observer design pattern which can use push or pull scenario, to inform those whom are registered for an event about its occurrence. Component: Post-Office = Message-Broker Post-Office-Box = Message-Storage-Validity Mailbox = Topic/Queue Postman !!! where's the postman ? Apache kafka act as a message broker which d...

Not all Ps sting

  If someone meant to say Ps and pronounce it Bees. would this confuse you :). Ps is for the P that is the start of Properties and Practice Each application should have some properties and follow certain practices. Properties: Below are 5 properties we should try to have in our application with a small description of how to include them Scalable, Scale => Increase workload (horizontally scaling) Statless, no state should be shared among different application instances,  Concurrency, concurrent processing = Threads. Loosely coupled, decompose the system into modules, each has minimal dependencies on each other "modularization", encapsulating code that changes together "High cohesion".  API first, Interfaces, implementation can be changed without affecting other application. favor distribution of work across different teams.  Backing Services, "DB, SMTP, FTP ..." , treating them as attached resources, meaning they can easily be changed. Manageable, changi...

String literal pool

I'm used to use String .format() when constructing a SQL statement, and a friend I knew likes to concatenate saying :"it's more readable to me". So String Objects are immutable, meaning that once they are created, they can't be altered. Concatenating 2 strings doesn't modify either Strings instead, it creates a new String "old ones are added to the string pool". String literals always have a reference to them in String Literal Pool, therefore not eligible for garbage collection. to concatenate use StringBuffer (Synchronized) or StringBuilder (not Synchronized) As both uses an internal array "so that new String Objects are not created". String literal Pool : String are stored in pool and before creating a new string  literals, compiler checks if such string already defined "used to optimize and save space". String literals : a sequence of characters between quotation marks.