Core Java Design Pattern : Structural Pattern : Bridge Design Pattern

• Bridge Design Pattern
• Examples

Decouple an abstraction from its implementation so that the two can vary independently.

Also Known As :Handle/Body

Use the Bridge pattern when

• you want to avoid a permanent binding between an abstraction and its implementation. This might be the case, for example, when the implementation must be selected or switched at run-time.
• both the abstractions and their implementations should be extensible by subclassing. In this case, the Bridge pattern lets you combine the different abstractions and implementations and extend them independently.
• changes in the implementation of an abstraction should have no impact on clients; that is, their code should not have to be recompiled.

The Bridge pattern decouples an abstraction from its implementation, so that the two can vary independently. A household switch controlling lights, ceiling fans, etc. is an example of the Bridge. The purpose of the switch is to turn a device on or off.

Switch.java

package com.javaskool;

// Interface with two methods -  on and off.

public interface Switch { 
  // Two positions of switch.
		public void switchOn();
		public void switchOff(); 
} 

//This switch can be implemented by various 
//devices in house, as Fan, Light Bulb etc. 
//Here is the sample code for that.

Fan.java

package com.javaskool;
//Implement the switch for Fan

public class Fan implements Switch { 
  // Two positions of switch.
	public void switchOn() {
	System.out.println("FAN Switched ON");
	} 
	public void switchOff() {
	System.out.println("FAN Switched OFF");
	}
}

Bulb.java

package com.javaskool;

//Implement the switch for Bulb

public class Bulb implements Switch { 
  // Two positions of switch.
	public void switchOn() {
	System.out.println("BULB Switched ON");
	} 
	public void switchOff() {
	System.out.println("BULB Switched OFF");
	}
} 

TestDrive.java

package com.javaskool;

public class TestDrive {

	public static void main(String[] args) {
		
		Switch phillips=new Fan();//bridge between switch and fan
		phillips.switchOn();
		phillips.switchOff();
		
		phillips=new Bulb();//bridge between switch and bulb
		phillips.switchOn();
		phillips.switchOff();
	}
}

Output

c:\>javac -d . *.java
c:\>java com.javaskool.TestDrive
FAN Switched ON
FAN Switched OFF
BULB Switched ON
BULB Switched OFF

UML Diagram for Fan-Switch Application having Implementation of Bridge Design Pattern

Download:

Bridge Design Pattern Code (6 KB)