Bridge pattern - Structural Design Pattern

Bridge Pattern

Bridge Pattern

Ref:-

http://www.tutorialspoint.com/design_pattern/bridge_pattern.htm

http://www.codeproject.com/Articles/42762/Bridge-Design-Pattern

Its a structural design pattern.

Just like how printers work with computers. If we have a USB cable (bridge), then we can connect any printer to any computer to start printing. It really doesn't matter if it's a laser printer or a color printer, either Windows PC or Mac.

 This pattern decouples implementation class and abstract class by providing a bridge structure between them.

This pattern involves an interface which acts as a bridge  , which makes the functionality of concrete classes independent from interface implementer classes. Both types of classes can be altered structurally without affecting each other. 

Implementation

We've an interface DrawAPI interface which is acting as a bridge implementer and concrete classes RedCircle, GreenCircle implementing the DrawAPI interface. Shape is an abstract class and will use object of DrawAPI. BridgePatternDemo, our demo class will use Shape class to draw different colored circle.

#### bridge interface acting as bridge between Shape and colors

public interface DrawAPI {

   public void drawCircle(int radius, int x, int y);

}

public class RedCircle implements DrawAPI {

   @Override

   public void drawCircle(int radius, int x, int y) {

      System.out.println("Drawing Circle[ color: red, radius: "

         + radius +", x: " +x+", "+ y +"]");

   }

}

public class GreenCircle implements DrawAPI {

   @Override

   public void drawCircle(int radius, int x, int y) {

      System.out.println("Drawing Circle[ color: green, radius: "

         + radius +", x: " +x+", "+ y +"]");

   }

}

public abstract class Shape {

   protected DrawAPI drawAPI;

   protected Shape(DrawAPI drawAPI){

      this.drawAPI = drawAPI;

   }

   public abstract void draw();

}

public class Circle extends Shape {

   private int x, y, radius;

   public Circle(int x, int y, int radius, DrawAPI drawAPI) {

      super(drawAPI);

      this.x = x;  

      this.y = y;  

      this.radius = radius;

   }

   public void draw() {

      drawAPI.drawCircle(radius,x,y);

   }

}

public class BridgePatternDemo {

   public static void main(String[] args) {

      Shape redCircle = new Circle(100,100, 10, new RedCircle());

      Shape greenCircle = new Circle(100,100, 10, new GreenCircle());

      redCircle.draw();

      greenCircle.draw();

   }

}