Question

A Java Problem. In this problem you are going write a class to model a traffic light that can cycle through colors, red, green, yellow. To do this, you will have to maintain the state of the traffic light. Maintaining state is one of the design pattern discussed in this week's lesson. The state of the TrafficLight indicates which light is lit. It changes every time the TrafficLight cycles.

Specification

TrafficLight will have a constructor that takes the x and y coordinates of the upper left hand corner of the rectangular part of the traffic light as parameters. The TrafficLight is black rectangle at the x,y coordinates with a width of 20 and a height of 60. There are red, green, and yellow circles inside the rectangle to look like a traffic light. The upper left hand corner of the red circle will be at same x,y coordinates as the box. The circles will touch the sides of the box and each other

Define an instance variable to hold the state (which light is lit). Make it an int. And define public constants for red, green, and yellow, named RED, GREEN, YELLOW (These will be ints also)

The constructor takes the x,y coordinates of the upper left hand corner of the TrafficLight as parameters and also sets the state of the light to red (using the constant).

Provide methods

1. public void cycle() changes the state (the color) in the following manner

If the state was red green yellow now it is green yellow red

2. public String getLight()gets the color (the current state) of the light as a string "red", "green" or "yellow"

3. public void draw(Graphics2D g2) draws the traffic light and fills the circles with a different color when the light is on or off

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TrafficLightComponent.java

import java.awt.Graphics;
import java.awt.Graphics2D;
import javax.swing.JComponent;

public class TrafficLightComponent extends JComponent
{

   private static final long serialVersionUID = 1L;
   
   public void paintComponent(Graphics g)
   {  
      // Recover Graphics2D
      Graphics2D g2 = (Graphics2D) g;
      
      TrafficLight signal = new TrafficLight( 10, 20);
      signal.draw(g2);
      String colorWord = (signal.getLight());
      g2.drawString(colorWord, 10, 100);

      
      TrafficLight signal2 = new TrafficLight( 60, 20);
      signal2.cycle();
      signal2.draw(g2);
      colorWord = signal2.getLight();
      g2.drawString(colorWord, 60, 100);
      
      TrafficLight signal3 = new TrafficLight( 110, 20);
      signal3.cycle();
      signal3.cycle();
      signal3.draw(g2);
      colorWord = signal3.getLight();
      g2.drawString(colorWord, 110, 100);
      
      TrafficLight signal4 = new TrafficLight( 160, 20);
      signal4.cycle();
      signal4.cycle();
      signal4.cycle();
      signal4.draw(g2);
      colorWord = signal4.getLight();
      g2.drawString(colorWord, 160, 100);
    
   }

    
}

TrafficLightViewer.java

import javax.swing.*;
public class TrafficLightViewer
{
   public static void main(String[] args)
   {
      JFrame frame = new JFrame();

      frame.setSize(300, 400);
      frame.setTitle("Traffic Lights");
      frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

      TrafficLightComponent component = new TrafficLightComponent();
      frame.add(component);

      frame.setVisible(true);
   }
}

Answer 1

import java.awt.Color;
import java.awt.Graphics2D;

public class TrafficLight {

   private static final int RED = 0;
   private static final int GREEN = 1;
   private static final int YELLOW = 2;
   private static final int WIDTH = 20;
   private static final int HEIGHT = 60;

   // Instance varibles
   private int x;
   private int y;
   private int light;

   /**
   * Constructor
   *
   * @param x
   *            - x coordinate of the traffic light
   * @param y
   *            - y coordinate of the traffic light
   */
   public TrafficLight(int x, int y) {
       this.x = x;
       this.y = y;
   }

   /**
   * Returns the current state of the light as "red", "green" or "yellow"
   */
   public String getLight() {
       if (this.light == RED)
           return "red";
       else if (this.light == GREEN)
           return "green";
       else if (this.light == YELLOW)
           return "yellow";
       else
           return "";
   }

   /**
   * Changes the current state of the traffic light to the next state if
   * current is RED, next will be GREEN if current is GREEN, next will be
   * YELLOW if current is YELLOW, next will be RED
   */
   public void cycle() {
       if (this.light == RED)
           this.light = GREEN;
       else if (this.light == GREEN)
           this.light = YELLOW;
       else if (this.light == YELLOW)
           this.light = RED;
   }

   /**
   * Draws a traffic light at x, y of Color c
   *
   * @param x
   *            - x coordinate of the light
   * @param y
   *            - y coordinate of the light
   * @param w
   *            - width of the light
   * @param h
   *            - height of the light
   * @param c
   *            - color of the light
   */
   private void drawLight(int x, int y, int w, int h, Color c, Graphics2D g2) {
       g2.setColor(c);
       g2.fillOval(x, y, w, h);
   }

   /**
   * Draws the traffic light
   */
   public void draw(Graphics2D g2) {
       // Draw the traffic light box
       g2.drawRect(x, y, WIDTH, HEIGHT);

       // Draw the lights
       if (this.light == RED) {
           // Set red color
           drawLight(x, y, WIDTH, WIDTH, Color.RED, g2);

           // Set yellow color for off
           drawLight(x, y + WIDTH, WIDTH, WIDTH, new Color(255, 165, 0), g2);

           // Set green color for off
           drawLight(x, y + WIDTH + WIDTH, WIDTH, WIDTH, new Color(85, 107, 47), g2);

       } else if (this.light == GREEN) {
           // Set red color
           drawLight(x, y, WIDTH, WIDTH, new Color(128, 0, 0), g2);

           // Set yellow color for off
           drawLight(x, y + WIDTH, WIDTH, WIDTH, new Color(255, 165, 0), g2);

           // Set green color for off
           drawLight(x, y + WIDTH + WIDTH, WIDTH, WIDTH, Color.GREEN, g2);

       } else if (this.light == YELLOW) {
           // Set red color
           drawLight(x, y, WIDTH, WIDTH, new Color(128, 0, 0), g2);

           // Set yellow color for off
           drawLight(x, y + WIDTH, WIDTH, WIDTH, Color.YELLOW, g2);

           // Set green color for off
           drawLight(x, y + WIDTH + WIDTH, WIDTH, WIDTH, new Color(85, 107, 47), g2);
       }
      
       // Reset color
       g2.setColor(Color.BLACK);
   }
}

SAMPLE OUTPUT:

Traffic Lights red green yellow red