Hands-On Design Patterns with Java

Programming the design pattern

The source code for the TrainStatus interface follows:

public interface TrainStatus {        public void activate();    public void deactivate();    public boolean isActivated();}

The source code for the NorthernTrain, EasternTrain, SouthernTrain, and WesternTrain classes is identical, so only the WesternTrain class is shown here:

public class WesternTrain implements TrainStatus {    private boolean activated;    public void activate() {        activated = true;        System.out.println("Train Status Update: Western Train Activated.");    }    public void deactivate() {        activated = false;        System.out.println("Train Status Update: Western Train Deactivated.");    }    public boolean isActivated() {        return activated;    }}

The NullObjectTrain class is slightly ...