FontysICT-sem1

Training Traffic Light (with an enum)

We are going to program traffic lights (again). If you have already done the TrafficLight Challenge from a previous chapter, especially if you copied the example code (with the errors in it) you will have noticed that using a String for the state (color) of a TrafficLight quickly leads to errors! For example, Orange, Orange and orange all accepted by the compiler but the values are different: this can cause all kinds of bugs: For example, take 2 TrafficLights, say trafficLight1 and trafficLight2. If the color of trafficLight1 has value Orange and the color of trafficLight2 has value Orange then an equation like

if (trafficLight1.color == trafficLight2.color) {
  ...
}

return false while the programmer expects true: A typo that can have major consequences for the behavior of the software. To avoid these bugs, we are going to use an Enum with them this time: By using an Enum, the compiler can help detect and detect and prevent them! For the color (state) of the TrafficLight, we will create an Enum:

public enum TrafficlightColors {
   Red,
   Orange,
   Green
}

Analysis

• The code is in English.
• I want to have the ability to create multiple objects of type TrafficLight, but I want to program it only once.
• A TrafficLight can have the colors (states) Green, Orange, Red: use English names for these states.
• For safety, when creating a TrafficLight, the state is always set to Red.
• From Red, the state can only become Green, then Orange, then Red again.

Design

• A class TrafficLight.
• This class has a private Field color of type TrafficlightColors.
• Initial value of color: TrafficlightColors.Red.
• The class gets a method NextState() that gives the TrafficLight the next value of color.
• We also want to be able to ask a TrafficLight what the current color is: public TrafficlightColors GetCurrentColor()

Realization

• Create the items listed in the design.
• The method NextState returns the color after changing the color: public TrafficlightColors NextState() {...}

A Console app has a main-method (public static void Main(string [] args)) in which you can put code like:

TrafficLight trafficLight = new TrafficLight();
// color has to be TrafficlightColors.Red.
Console.WriteLine(trafficLight.GetCurrentcolor());
trafficLight.NextState();
// color has to be TrafficlightColors.Green.
Console.WriteLine(trafficLight.GetCurrentColor());
trafficLight.NextState();
// color has to be TrafficlightColors.Orange.
Console.WriteLine(trafficLight.GetCurentColor());
trafficLight.NextState();
// and TrafficlightColors.Red again!
Console.WriteLine(trafficLight.GetCurentColor());

Is this code sloppily put together? Look carefully for errors! Correct them if necessary and test the program. Can you think of any improvements to the program?

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