Bridge pattern

Bridge pattern

The bridge pattern is a design pattern used in software engineering which is meant to "decouple an abstraction from its implementation so that the two can vary independently".[1] The bridge uses encapsulation, aggregation, and can use inheritance to separate responsibilities into different classes.

When a class varies often, the features of object-oriented programming become very useful because changes to a program's code can be made easily with minimal prior knowledge about the program. The bridge pattern is useful when both the class as well as what it does vary often. The class itself can be thought of as the implementation and what the class can do as the abstraction. The bridge pattern can also be thought of as two layers of abstraction.

The bridge pattern is often confused with the adapter pattern. In fact, the bridge pattern is often implemented using the class adapter pattern, e.g. in the Java code below.

Variant: The implementation can be decoupled even more by deferring the presence of the implementation to the point where the abstraction is utilized.

Contents

Structure

Bridge UML class diagram.svg

Abstraction
defines the abstract interface
maintains the Implementor reference
RefinedAbstraction
extends the interface defined by Abstraction
Implementor
defines the interface for implementation classes
ConcreteImplementor
implements the Implementor interface


Bridge in LePUS3 (legend)

Example

The following Java (SE 6) program illustrates the 'shape' example given below and will output:

API1.circle at 1.000000:2.000000 radius 7.500000
API2.circle at 5.000000:7.000000 radius 27.500000
/** "Implementor" */
interface DrawingAPI {
    public void drawCircle(double x, double y, double radius);
}
 
/** "ConcreteImplementor"  1/2 */
class DrawingAPI1 implements DrawingAPI {
   public void drawCircle(double x, double y, double radius) {
        System.out.printf("API1.circle at %f:%f radius %f\n", x, y, radius);
   }
}
 
/** "ConcreteImplementor" 2/2 */
class DrawingAPI2 implements DrawingAPI {
   public void drawCircle(double x, double y, double radius) { 
        System.out.printf("API2.circle at %f:%f radius %f\n", x, y, radius);
   }
}
 
/** "Abstraction" */
interface Shape {
   public void draw();                             // low-level
   public void resizeByPercentage(double pct);     // high-level
}
 
/** "Refined Abstraction" */
class CircleShape implements Shape {
   private double x, y, radius;
   private DrawingAPI drawingAPI;
   public CircleShape(double x, double y, double radius, DrawingAPI drawingAPI) {
       this.x = x;  this.y = y;  this.radius = radius; 
       this.drawingAPI = drawingAPI;
   }
 
   // low-level i.e. Implementation specific
   public void draw() {
        drawingAPI.drawCircle(x, y, radius);
   }   
   // high-level i.e. Abstraction specific
   public void resizeByPercentage(double pct) {
        radius *= pct;
   }
}
 
/** "Client" */
class BridgePattern {
   public static void main(String[] args) {
       Shape[] shapes = new Shape[] {
           new CircleShape(1, 2, 3, new DrawingAPI1()),
           new CircleShape(5, 7, 11, new DrawingAPI2()),
       };
 
       for (Shape shape : shapes) {
           shape.resizeByPercentage(2.5);
           shape.draw();
       }
   }
}

See also

References

  1. ^ Gamma, E, Helm, R, Johnson, R, Vlissides, J: Design Patterns, page 151. Addison-Wesley, 1995

External links


Wikimedia Foundation. 2010.

Игры ⚽ Поможем написать реферат

Look at other dictionaries:

  • Bridge (disambiguation) — A bridge is a structure built so that a transportation route can cross above an obstacle.Bridge can also refer to:In entertainment*Bridge (card game disambiguation), multiple card games *Bridge (instrument), the device that anchors the strings to …   Wikipedia

  • Bridge (dentistry) — Intervention ICD 9 CM 23.42 23.43 MeSH …   Wikipedia

  • Pattern Recognition (novel) — infobox Book | name = Pattern Recognition image caption = Original 1st edition cover author = William Gibson cover artist = country = United States language = English series = genre = Science fiction novel publisher = G. P. Putnam s Sons release… …   Wikipedia

  • bridge — bridge1 bridgeable, adj. bridgeless, adj. bridgelike, adj. /brij/, n., v., bridged, bridging, adj. n. 1. a structure spanning and providing passage over a river, chasm, road, or the like. 2. a connecting, transitional, or intermediate route or… …   Universalium

  • Pattern 1914 Enfield — Rifle, .303 Pattern 1914 Pattern 1914 Enfield Type Service rifle Place of origin …   Wikipedia

  • Strategy pattern — [ LePUS3 ( [http://lepus.org.uk/ref/legend/legend.xml legend] ) ] In computer programming, the strategy pattern (also known as the policy pattern) is a particular software design pattern, whereby algorithms can be selected at runtime.In some… …   Wikipedia

  • Design Pattern — Patron de conception Pour les articles homonymes, voir Patron. Un patron de conception (design pattern en anglais) est un concept de génie logiciel destiné à résoudre les problèmes récurrents suivant le paradigme objet. En français on utilise… …   Wikipédia en Français

  • Design pattern — Patron de conception Pour les articles homonymes, voir Patron. Un patron de conception (design pattern en anglais) est un concept de génie logiciel destiné à résoudre les problèmes récurrents suivant le paradigme objet. En français on utilise… …   Wikipédia en Français

  • Structural pattern — In Software Engineering, Structural Design Patterns are Design Patterns that ease the design by identifying a simple way to realize relationships between entities.Examples of Structural Patterns include:* Adapter pattern: adapts one interface for …   Wikipedia

  • Glossary of contract bridge terms — These terms are used in Contract bridge[1][2] , or the earlier game Auction bridge, using duplicate or rubber scoring. Some of them are also used in Whist, Bid whist, and other trick taking games. This glossary supplements the Glossary of card… …   Wikipedia

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”