The Builder patternThe Builder pattern

Shuanghui LuoShuanghui Luo

Type & intentType & intent

• One of the Creational PatternOne of the Creational Pattern

• Intent:Intent: Separates the construction of a Separates the construction of a

complex object from its complex object from its representation so that the same representation so that the same construction process can create construction process can create different representations.different representations.

ApplicabilityApplicability

• The Builder pattern assembles a number of The Builder pattern assembles a number of objects in various ways depending on the data. objects in various ways depending on the data.

• Use the Builder pattern whenUse the Builder pattern when

the algorithm for creating a complex object the algorithm for creating a complex object should be independent on the parts that make should be independent on the parts that make up the object and how they're assembled. up the object and how they're assembled.

the construction process must allow different the construction process must allow different representations for the object that's representations for the object that's constructed.constructed.

Structure (UML Model)Structure (UML Model)

the complex object the complex object

under construction. under construction.

construct an object construct an object

using the Builderusing the Builder

interface interface

constructs constructs

and assembles parts of the and assembles parts of the

product by implementing the Builderproduct by implementing the Builder

interface interface

specifies an abstractspecifies an abstract

interface for creating parts interface for creating parts

of a Product objectof a Product object

• Builder: Builder: specifies an abstract interface for specifies an abstract interface for creating parts of a Product object. creating parts of a Product object.

• ConcreteBuilder: ConcreteBuilder: constructs and assembles parts of the product by constructs and assembles parts of the product by

implementing the Builder interface. implementing the Builder interface. Defines and keeps track of the representation it Defines and keeps track of the representation it

creates.creates. Provides an interface for retrieving the product.Provides an interface for retrieving the product.

• Director: Director: constructs an object using the Builder constructs an object using the Builder interface. interface.

• Product: Product: represents the complex object under represents the complex object under construction. construction.

ParticipantsParticipants

ConsequencesConsequences• Abstracts the construction implementation details Abstracts the construction implementation details

of a class type. It lof a class type. It lets you vary the internal ets you vary the internal representation of the product that it builds. representation of the product that it builds.

• Encapsulates the way in which objects are Encapsulates the way in which objects are constructed improving the modularity of a system.constructed improving the modularity of a system.

• Finer control over the creation process, by letting a Finer control over the creation process, by letting a builder class have multiple methods that are called builder class have multiple methods that are called in a sequence to create an object.in a sequence to create an object.

• Each specific Builder is independent of any others.Each specific Builder is independent of any others.

Example (1)Example (1)

• A fathers-sons chooserA fathers-sons chooser

We have a list of fathers in a JlistWe have a list of fathers in a Jlist

We want to create a visual chooser for We want to create a visual chooser for sons of the selected father:sons of the selected father:

A JPanel with a JList, if sons>3A JPanel with a JList, if sons>3

A JPanel with JCheckBoxes, if sons<=3A JPanel with JCheckBoxes, if sons<=3

Example (2)Example (2)

Example (3)Example (3)public class MainJPanel extends JPanel implements

javax.swing.event.ListSelectionListener{

…public void valueChanged(javax.swing.event.ListSelectionEvent e){

…this.getSonsPanel().add(this.getCDirector().getChoiceUI(v));this.getSonsPanel().validate();this.getSonsPanel().repaint();

}

…

}

Get one of the GUIsGet one of the GUIs

Example (4)Example (4)public class ChoiceDirector public class ChoiceDirector {{

……public javax.swing.JPanel getChoiceUI(java.util.Vector choices)public javax.swing.JPanel getChoiceUI(java.util.Vector choices){{

ChoiceAbstractBuilder p;ChoiceAbstractBuilder p;

if (choices.size() <= 3)if (choices.size() <= 3){{

p= new CheckBoxChoiceConcreteBuilder(choices);p= new CheckBoxChoiceConcreteBuilder(choices);}}elseelse{{

p= new ListChoiceConcreteBuilder(choices);p= new ListChoiceConcreteBuilder(choices);}}

return p.getGUI();return p.getGUI();}}……

}}

The abstract builderThe abstract builder

Concrete buildersConcrete builders

Builds GUIBuilds GUI

ReferencesReferences• http://hillside.net/patternshttp://hillside.net/patterns

• http://www.cs.wustl.edu/~schmidt/patterns.htmlhttp://www.cs.wustl.edu/~schmidt/patterns.html

• http://www.ciol.com/content/technology/sw_desg_patt/toc.asphttp://www.ciol.com/content/technology/sw_desg_patt/toc.asp

• http://www.research.umbc.edu/~tarr/cs491/fall00/cs491.htmlhttp://www.research.umbc.edu/~tarr/cs491/fall00/cs491.html

• http://www.fh-konstanz.de/studium/ze/cim/projekte/osefa/http://www.fh-konstanz.de/studium/ze/cim/projekte/osefa/patterns/builder/intent.htmpatterns/builder/intent.htm

• http://www.cs.washington.edu/homes/bdudash/http://www.cs.washington.edu/homes/bdudash/designpatterns/builder.htmldesignpatterns/builder.html