// Introduced in Chapter 3/** A colored light bulb. */public class ColoredLight extends Light {  /** Color of the ColoredLight. */  private char color;  /** Set the color randomly to one of 'R', 'G', or 'B'. */  public ColoredLight() {    super();    int x = (int)(Math.random() * 3);    switch (x) {      case 0:        color = 'R';        break;      case 1:        color = 'G';        break;      default:        color = 'B';    }  }    /** Return the color of this ColoredLight. */  public char getColor() {    return color;  }    public String toString() {    if (isOn()) {      return "" + color;    } else {      return ".";    }  }}