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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" (Gamma et al. In Software engineering, a design pattern is a general reusable solution to a commonly occurring problem in Software design. Software engineering is the application of a systematic disciplined quantifiable approach to the development operation and maintenance of Software. In Computer science, abstraction is a mechanism and practice to reduce and factor out details so that one can focus on a few concepts at a time Implementation is the realization of an application or execution of a Plan, idea Model, Design, Specification, standard, Algorithm ). The bridge uses encapsulation, aggregation, and can use inheritance to separate responsibilities into different classes. In Computer science, object composition (not to be confused with function composition) is a way and practice to combine simple objects or In Object-oriented programming, inheritance is a way to form new classes (instances of which are called objects using classes that have already been defined In Object-oriented programming, a class is a Programming language construct that is used as a blueprint to create objects This blueprint includes attributes

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. Object-oriented programming (OOP is a Programming paradigm that uses " objects " and their interactions to design applications and computer programs Computer programs (also software programs, or just programs) are instructions for a Computer. In Computer science, source code (commonly just source or code) is any sequence of statements or declarations written in some Human-readable The bridge pattern is useful when not only the class itself varies often but also what the class does. The class itself can be thought of as the implementation and what the class can do as the abstraction.

Variant: The implementation can be decoupled even more by deferring the presence of the implementation to the point where the abstraction is utilized (as illustrated by the Visual Prolog example below).

Contents

Non-technical examples

Shape abstraction

When the abstraction and implementation are separated, they can vary independently. Consider the abstraction of shapes. There are many types of shapes, each with its own properties. And there are things that all shapes do. One thing all shapes can do is draw themselves. However, drawing graphics to a screen can sometimes be dependent on different graphics implementations or operating systems. Shapes have to be able to be drawn on many types of operating systems. Having the shape itself implement them all, or modifying the shape class to work with different architectures is not practical. The bridge helps by allowing the creation of new implementation classes that provide the drawing implementation. The abstraction class, shape, provides methods for getting the size or properties of a shape. The implementation class, drawing, provides an interface for drawing graphics. If a new shape needs to be created or there is a new graphics API to be drawn on, then it is very easy to add a new implementation class that implements the needed features. [1]

Car abstraction

Imagine two types of cars (the abstraction), a Jaguar and a Mercedes (both are Refinements of the Abstraction). The Abstraction defines that a Car has features such as tires and an engine. Refinements of the Abstraction declare what specific kind of tires and engine it has.
Finally, there are two types of road. The road is the Implementor (see image below). A highway and an interstate highway are the Implementation Details. Any car refinement needs to be able to drive on any type of road; this concept is what the Bridge Pattern is all about.

Structure

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

Code examples

Java

The following Java (SE 6) program illustrates the 'shape' example given above 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[2];
       shapes[0] = new CircleShape(1, 2, 3, new DrawingAPI1());
       shapes[1] = new CircleShape(5, 7, 11, new DrawingAPI2());
 
       for (Shape shape : shapes)
       {
           shape. resizeByPercentage(2. 5);
           shape. draw();
       }
   }
}

C#

The following C# program illustrates the "shape" example given above and will output:

API1. C# (pronounced C Sharp is a Multi-paradigm C# (pronounced C Sharp is a Multi-paradigm circle at 1:2 radius 7. 5
API2. circle at 5:7 radius 27. 5

using System;
 
 /** "Implementor" */
 interface IDrawingAPI {
    void DrawCircle(double x, double y, double radius);
 }
 
 /** "ConcreteImplementor" 1/2 */
 class DrawingAPI1 : IDrawingAPI {
    public void DrawCircle(double x, double y, double radius) 
    {
        System. Console. WriteLine("API1. circle at {0}:{1} radius {2}", x, y, radius); 
    }
 }
 
 /** "ConcreteImplementor" 2/2 */
 class DrawingAPI2 : IDrawingAPI 
 {
    public void DrawCircle(double x, double y, double radius) 
    { 
        System. Console. WriteLine("API2. circle at {0}:{1} radius {2}", x, y, radius); 
    }
 }
 
 /** "Abstraction" */
 interface IShape {
    void Draw();                             // low-level (i. e.  Implementation-specific)
    void ResizeByPercentage(double pct);     // high-level (i. e.  Abstraction-specific)
 }
 
 /** "Refined Abstraction" */
 class CircleShape : IShape {
    private double x, y, radius;
    private IDrawingAPI drawingAPI;
    public CircleShape(double x, double y, double radius, IDrawingAPI 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) {
        IShape[] shapes = new IShape[2];
        shapes[0] = new CircleShape(1, 2, 3, new DrawingAPI1());
        shapes[1] = new CircleShape(5, 7, 11, new DrawingAPI2());
 
        foreach (IShape shape in shapes) {
            shape. ResizeByPercentage(2. 5);
            shape. Draw();
        }
    }
 }

C# using generics

The following C# program illustrates the "shape" example given above and will output:

API1. C# (pronounced C Sharp is a Multi-paradigm C# (pronounced C Sharp is a Multi-paradigm circle at 1:2 radius 7. 5
API2. circle at 5:7 radius 27. 5

using System;
 
 /** "Implementor" */
 interface IDrawingAPI {
    void DrawCircle(double x, double y, double radius);
 }
 
 /** "ConcreteImplementor" 1/2 */
 struct DrawingAPI1 : IDrawingAPI {
    public void DrawCircle(double x, double y, double radius) 
    {
        System. Console. WriteLine("API1. circle at {0}:{1} radius {2}", x, y, radius); 
    }
 }
 
 /** "ConcreteImplementor" 2/2 */
 struct DrawingAPI2 : IDrawingAPI 
 {
    public void DrawCircle(double x, double y, double radius) 
    { 
        System. Console. WriteLine("API2. circle at {0}:{1} radius {2}", x, y, radius); 
    }
 }
 
 /** "Abstraction" */
 interface IShape {
    void Draw();                             // low-level (i. e.  Implementation-specific)
    void ResizeByPercentage(double pct);     // high-level (i. e.  Abstraction-specific)
 }
 
 /** "Refined Abstraction" */
 class CircleShape<T> : IShape
    where T : struct, IDrawingAPI
 {
    private double x, y, radius;
    private static IDrawingAPI drawingAPI = new T();
    public CircleShape(double x, double y, double radius) 
    {
        this. x = x;  this. y = y;  this. radius = radius;
    }
    // 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) {
        IShape[] shapes = new IShape[2];
        shapes[0] = new CircleShape<DrawingAPI1>(1, 2, 3);
        shapes[1] = new CircleShape<DrawingAPI2>(5, 7, 11);
 
        foreach (IShape shape in shapes) {
            shape. ResizeByPercentage(2. 5);
            shape. Draw();
        }
    }
 }


C++

The following C++ program illustrates the "shape" example given above and will output:

API1. circle at 1:2 7. 5
API2. circle at 5:7 27. 5

#include <iostream>
 
using namespace std;
 
/* Implementor*/
class DrawingAPI {
  public:
   virtual void drawCircle(double x, double y, double radius) = 0;
   virtual ~DrawingAPI(){};
};
 
/* Concrete ImplementorA*/
class DrawingAPI1 : public DrawingAPI {
  public:
   void drawCircle(double x, double y, double radius) {
      cout << "API1. circle at " << x << ":" << y << " " << radius << endl;
   }
};
 
/* Concrete ImplementorB*/
class DrawingAPI2 : public DrawingAPI {
public:
   void drawCircle(double x, double y, double radius) {
      cout << "API2. circle at " << x << ":" << y << " " <<  radius << endl;
   }
};
 
/* Abstraction*/
class Shape {
  public:
   virtual ~Shape() {};
   virtual void draw() = 0;
   virtual void resizeByPercentage(double pct) = 0;
};
 
/* Refined Abstraction*/
class CircleShape : public Shape {
  public:
   CircleShape(double x, double y,double radius, DrawingAPI *drawingAPI){
      m_x = x;
      m_y = y;
      m_radius = radius;
      m_drawingAPI = drawingAPI;
   }
   void draw() {
      m_drawingAPI->drawCircle(m_x,m_y,m_radius);
   }
   void resizeByPercentage(double pct) {
      m_radius *= pct;
   }
  private:
   double m_x,m_y,m_radius;
   DrawingAPI *m_drawingAPI;
};
 
int main(void) {
   DrawingAPI1 dap1;
   DrawingAPI2 dap2;
   CircleShape circle1(1,2,3,&dap1);
   CircleShape circle2(5,7,11,&dap2);
   circle1. resizeByPercentage(2. 5);
   circle2. resizeByPercentage(2. 5);
   circle1. draw();
   circle2. draw();
   return 0;
}

See also

External links

References

  1. ^ Shalloway; Trott. Design Patterns Explained: A New Perspective on Object-Oriented Design.  
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