The Builder pattern

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The Builder pattern

• Shuanghui Luo

2
Type intent

• One of the Creational Pattern
• Intent
• Separates the construction of a complex object
  from its representation so that the same
  construction process can create different
  representations.

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Applicability

• The Builder pattern assembles a number of objects
  in various ways depending on the data.
• Use the Builder pattern when
• the algorithm for creating a complex object
  should be independent on the parts that make up
  the object and how they're assembled.
• the construction process must allow different
  representations for the object that's
  constructed.

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Structure (UML Model)
5
Participants

• Builder specifies an abstract interface for
  creating parts of a Product object.
• ConcreteBuilder
• constructs and assembles parts of the product by
  implementing the Builder interface.
• Defines and keeps track of the representation it
  creates.
• Provides an interface for retrieving the product.
• Director constructs an object using the Builder
  interface.
• Product represents the complex object under
  construction.

6
Consequences

• Abstracts the construction implementation details
  of a class type. It lets you vary the internal
  representation of the product that it builds.
• Encapsulates the way in which objects are
  constructed improving the modularity of a system.
• Finer control over the creation process, by
  letting a builder class have multiple methods
  that are called in a sequence to create an
  object.
• Each specific Builder is independent of any
  others.

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Example (1)

• A fathers-sons chooser
• We have a list of fathers in a Jlist
• We want to create a visual chooser for sons of
  the selected father
• A JPanel with a JList, if sonsgt3
• A JPanel with JCheckBoxes, if sonslt3

8
Example (2)
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Example (3)

• public class MainJPanel extends JPanel implements
  javax.swing.event.ListSelectionListener
• public void valueChanged(javax.swing.event.ListSe
  lectionEvent e)
• this.getSonsPanel().add(this.getCDirector().getC
  hoiceUI(v))
• this.getSonsPanel().validate()
• this.getSonsPanel().repaint()

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Example (4)

• public class ChoiceDirector
• public javax.swing.JPanel getChoiceUI(java.util.V
  ector choices)
• ChoiceAbstractBuilder p
• if (choices.size() lt 3)
• p new CheckBoxChoiceConcreteBuilder(choices)
• else
• p new ListChoiceConcreteBuilder(choices)
• return p.getGUI()

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References

• http//hillside.net/patterns
• http//www.cs.wustl.edu/schmidt/patterns.html
• http//www.ciol.com/content/technology/sw_desg_pat
  t/toc.asp
• http//www.research.umbc.edu/tarr/cs491/fall00/cs
  491.html
• http//www.fh-konstanz.de/studium/ze/cim/projekte/
  osefa/patterns/builder/intent.htm
• http//www.cs.washington.edu/homes/bdudash/designp
  atterns/builder.html