August 19, 2003

Creation Factory – Builder

“Separate the construction of a complex object from its representation so that the same construction process can create different representations”

  • Used when an object can be created in a variety of ways, or involves lots of steps
  • The builder only has one job: fill in the object with data from some other location
  • It is familiar with the target object and the input source.
  • Can be a method or a class
  • Classes can leverage inheritance for common functions when working with the target object.

public class Builder {

virtual Portfolio Build();


Now data can be accessed from various sorces – DB, file, Web service etc. How can be builder class controoled – again you can use here Factory Pattern discussed:

public class BuilderFactory


BuilderFactory() {}

virtual Builder DBBuilder(IDBConnection db);

virtual Builder WebServiceBuilder(string URL);

virtual Builder ScraperBuilder(string URL);


And here is how Builder Factoy Implemented:

static void Main() {

BuilderFactory factory;

Builder builder;

switch( typeBuild ) {

case “DB”: builder = factory.DBBuilder(db);

case "WebService": builder = factory.WebServiceBuilder(url);


Portfolio portfolio = builder.Build();


From above example –

  1. The caller only will care about the base class.
  2. Some of the creation details should be hidden