ADAPTER. Topics. Presented By: Mallampati Bhava Chaitanya

Transcription

1 ADAPTER Presented By: Mallampati Bhava Chaitanya Topics Intent Motivation Applicability Structure Participants & Collaborations Consequences Sample Code Known Uses Related Patterns

2 Intent Convert the interface of a class into another interface clients expect. Adapter lets classes work together that couldn t work otherwise because of incompatible interfaces. Motivation Problem: Toolkit class that s designed for reuse isn t reusable only because its interface doesn t match the domain specific interface an application requires. Solution: Better Solution: We can make toolkit to adopt domain specific interfaces to make Adapter that application work!@#

3 Example: Drawing Editor Applicability: When to use adapter? You want to use an existing class and its interface doesn t match the one you need You want to create a reusable class that cooperates with unrelated or unforeseen classes, that is, classes that don t necessarily have compatible interfaces. You need to use several existing subclasses, but its impractical to adapt their interface by subclassing every one. An object adapter can adapt the interface of its parent class.

4 Structure Class Adapter Object Adapter Participants & Collaborations Participants: Target (Shape) Defines the domain-specific interface that client uses. Client (DrawingEditor) Colloborates with objects conforming to the Target Interface Adaptee (TextView) Defines an existing interface that needs adapting Adapter (TextShape) Adapts the interface of Adaptee to the Target Interface Collaborations: Clients call operations on an Adapter instance. In turn, the adapter calls Adaptee operations that carry out the request.

5 Consequences Class Adapter Adapts Adaptee to Target by committing to a concrete Adaptee class. As a consequence a class adapter wont work when we want to adapt a class and all its sub classes Lets adapter override some of Adaptee s behaviour, since Adapter is a subclass of Adaptee Introduces only one object, and no additional pointer indirection is needed to get to the adaptee Consequences Object Adapter Lets single Adapter work with many Adaptees - that is, the Adaptee itself and all of its subclasses(if any). The Adapter can also add functionality to all its Adaptees at once. Makes it harder to override Adaptee behavior. It will require subclassing Adaptee and making Adapter refer to the subclass rather than the Adaptee itself.

6 Sample Code // Interface Shape package dpj.structural.adapter; import dpj.structural._common.point; import dpj.structural._common.manipulator; // interface Shape public interface Shape public abstract void BoundingBox (Point bottomleft, Point topright); // public abstract Manipulator CreateManipulator (); // interface Shape ============================================================= // Class TextView package dpj.structural.adapter; import dpj.structural._common.point; public class TextView public TextView () public void GetOrigin (Integer x, Integer y) public void GetExtent (Integer width, Integer height) public boolean isempty () return false; // class TextView Class Adapter (uses multiple inheritance to adapt interfaces) // Class TextShape package dpj.structural.adapter.classadapter; import dpj.structural._common.point; import dpj.structural._common.manipulator; import dpj.structural.adapter.shape; import dpj.structural.adapter.textview; public class TextShape extends TextView implements Shape public TextShape () public void BoundingBox (Point bottomleft, Point topright) Integer bottom = null, left = null, width = null, height = null; GetOrigin (bottom, left); GetExtent (width, height); bottomleft = new Point (bottom.intvalue (), left.intvalue ()); topright = new Point (bottom.intvalue () + height.intvalue (), left.intvalue () + width.intvalue ()); // BoundingBox public Manipulator CreateManipulator () return new TextManipulator (this); public boolean isempty () return super.isempty (); // class TextShape // Class TextManipulator package dpj.structural.adapter.classadapter; import dpj.structural._common.manipulator; public class TextManipulator extends Manipulator public TextManipulator (TextShape shape) // class TextManipulator

7 Object Adapter (uses object composition to combine classes with different Interfaces) // Class TextShape package dpj.structural.adapter.objectadapter; import dpj.structural._common.point; import dpj.structural.adapter.shape; import dpj.structural.adapter.textview; import dpj.structural._common.manipulator; public class TextShape implements Shape public TextShape (TextView vu) textvu = vu; vu = new TextView (); public void BoundingBox (Point bottomleft, Point topright) Integer bottom = null, left = null, width = null, height = null; textvu.getorigin (bottom, left); textvu.getextent (width, height); bottomleft = new Point (bottom.intvalue (), left.intvalue ()); topright = new Point (bottom.intvalue () + height.intvalue (), left.intvalue () + width.intvalue ()); // BoundingBox public Manipulator CreateManipulator () return new TextManipulator (this); public boolean isempty () return textvu.isempty (); private TextView textvu; // class TextShape Known Uses ET++ Draw InterViewer2.6 GraphicBlock adapts the interface of the Graphic class to that of Interactor. The GraphicBlock lets a Graphic instance be displayed, scrolled,and zoomed within an Interactor structur.

8 Related Patterns Bridge It is meant to separate an interface from its implementation so that they can be varied easily and independently Where as an Adapter is meant to change the interface of an existing object. Decorator Enhances another onject without changing its interface Proxy Defines a representative or surrogate for another object and does not change its interface. References Design Paterns by Erich Gamma, Richard Helm, Rolph Johnson, John Vlissides Adapter - /adapter/ Overview of Design Patterns - es1_2ed.html#adapter

9 Thank You