In Bridge pattern i have read "decouples abstraction from implementation so that both can vary independently". what does it mean really ? and how does this phrase related to the Bridge pattern example given below? i understand this code but unable to relate this code with phrase. can anyone explain this.
Thanks.
/* Implementor interface*/
interface Gear
{
void handleGear();
}
/* Concrete Implementor - 1 */
class ManualGear implements Gear{
public void handleGear(){
System.out.println("Manual gear");
}
}
/* Concrete Implementor - 2 */
class AutoGear implements Gear{
public void handleGear(){
System.out.println("Auto gear");
}
}
/* Abstraction (abstract class) */
abstract class Vehicle {
Gear gear;
public Vehicle(Gear gear){
this.gear = gear;
}
abstract void addGear();
}
/* RefinedAbstraction - 1*/
class Car extends Vehicle{
public Car(Gear gear){
super(gear);
// initialize various other Car components to make the car
}
public void addGear(){
System.out.print("Car handles ");
gear.handleGear();
}
}
/* RefinedAbstraction - 2 */
class Truck extends Vehicle{
public Truck(Gear gear){
super(gear);
// initialize various other Truck components to make the car
}
public void addGear(){
System.out.print("Truck handles " );
gear.handleGear();
}
}
/* Client program */
public class BridgeDemo {
public static void main(String args[]){
Gear gear = new ManualGear();
Vehicle vehicle = new Car(gear);
vehicle.addGear();
gear = new AutoGear();
vehicle = new Car(gear);
vehicle.addGear();
gear = new ManualGear();
vehicle = new Truck(gear);
vehicle.addGear();
gear = new AutoGear();
vehicle = new Truck(gear);
vehicle.addGear();
}
}
output
Car handles Manual gear
Car handles Auto gear
Truck handles Manual gear
Truck handles Auto gear
