design patterns

interesting topics during design pattern lectures

implmenetation by intentions

public void printReport (String CustomerID) { 
    if(!isValid(CustomerID)) throw new ArgumentException(); 
    Employee[] emps = getEmployees(CustomerID);
    if(needsSorting(emps)) 
        sortEmployees(emps); 
    printHeader(CustomerID);
    printFormattedEmployees(emps);
    printFooter(CustomerID);
}

one public method contains multiple private methods fulfilling one specifc logic at a time. it’s your logical sequences when you implement printReport in your head. by doing this you can achieve

• Method cohesion
• separation of concerns
  • sergeant method: calls other methods
  • private methods: implementing code
• clarity - clear code is better than comments
• easy in finding/forming certain patterns
• no extra work is required

Commonality-Variability Analysis, CVA

Assume you start a new project solving software problem in a certain domain. you heard bunch of requirments from your clients. how would you find a entities, create an abstraction with whom, find a suitable patterns among them.

at this time CVA can help you

requirements

• US Tax
• Canadian PST, GST
• Validation of addresses strcuture in different locations

from this requirments you can derive a following potential entities and abstractions.

examle of CVA:

Country
----
US
Canada

Tax
-----
Canadian Province
Canadian Fed
US

AddressValidation
------
US
Canada