CS 161 Lab #2

Goals:

Directions:

1. Download the Face project and extract its contents, then start BlueJ and open the project. (You can use the BlueJ copy you installed on Alexandria last week, or the version that's already installed on the lab machines. The local copy should run more quickly.)
2. Create a new Face object by right-clicking on the Face class in the project window and selecting "new Face()". Right click on the resulting face object (the red rectangle on the workbench), invoke the draw method, and verify that it draws a colored face like the one below. Experiment with the setBlackAndWhite() and setColor() methods until you're sure you understand what they do to the picture.
   
3. The face is pretty nice, but some may question the choice of green for the nose. A scientific poll of Tacoma residents shows massive disagreement regarding preferred nose colors. To keep them all happy, let's change the constructor so that it takes a parameter. We'll pass the desired color to the constructor when we create a Face, and use the parameter to determine the nose's color. It'll take a couple of steps to pull this off: We need a field to remember the nose's color, we need to modify the existing constructor so that it takes a parameter and stores it in the field for future reference. Finally, we need to modify the draw method so that it uses this new color information when drawing the nose.
   • Go to the top of the Face class and add a new String field called noseColor. Take a look at the color field in the Circle class if you need some help — our field declaration will look just the same, except for the field's name.
   • Next, change the constructor's signature — edit the first line of the constructor so that it expects a parameter called color of type String. You can look at the changeColor method in the Circle class for inspiration if you like — it's an example of a method that expects a color to be passed as an argument. (They call their parameter newColor, but we'll just call ours color.) Do not add a changeColor method to your Face class though. The goal here is to modify the constructor so that it takes an argument specifying the color of the nose.
   • We don't create or draw the nose in the constructor — that doesn't happen until the draw method is invoked — but draw can't see the constructor's parameter. (Parameters, like locally-declared variables are only visible within a particular method.) That is, the user told the constructor what color they wanted the nose to be, but we need to get that information to the other methods in the class. We'll use an assignment statement to store the nose color in a field, and access the field in draw when restoring the nose's color. For now, just add this line to the constructor:

     noseColor = color;

     This will take the parameter's value and store it in our noseColor field.
   • Finally, add a statement to the draw method that will change the nose's color to noseColor.
   • When you've finished with the changes, make sure the Face class still compiles. Create and draw face objects with several different nose colors and verify that the nose comes out in the desired color.

4. It seems a shame that our face doesn't have a mouth. Spend a few minutes extending the code to add a mouth. You'll need to add a new field at the top of the class in which to store the mouth object (you can choose what kind of object to use), and some new lines in the draw method that create the mouth and put it where it should be. (Don't worry about extending the setBlackAndWhite or setColor methods to deal with the mouth for now.) Make sure your mouth-drawing code works before going to the next step.
5. Lots of people have gotten used to the mouthless face, and they may not appreciate the new addition. As a final act, let's make the mouth optional. We can do this by passing a second argument to the constructor — a boolean that specifies whether we want the mouth to be created or not.
   • Add a new field at the top of the class called drawMouth to hold the new boolean value, and write an assignment statement in the constructor that stores the parameter's value into the field.
   • Modify the constructor's signature again to add another parameter — in this case, a boolean named isMouth. When passing more than one parameter, the arguments must be separated by a comma. (See Triangle's changeSize method for an example of this.)
   • In draw, write an if statement that encloses the mouth-drawing statements. The basic format is as follows:

     if (drawMouth) {
        // Statements that draw the mouth
     }
     

• Experiment with statement ordering. What happens if you move all of the makeVisible calls to the end of the draw method? To the beginning of the method?
• There's a flaw in our nose-coloring plan: The nose is initially drawn in the color specified by the user, but if the face is converted to black and white and then back to color, it always gets redrawn in green. Modify setColor so that the nose comes out to be noseColor. (You can modify setBlackAndWhite to make a white nose while you're at it, too.)
• Extend the setBlackAndWhite method so that it makes the mouth white. This is trickier than it sounds, since there isn't always a mouth! You can use an if(mouth != null) statement inside the if(head != null) statement to control whether you try to set the mouth to white.
• Fix the setColor method so that sets the mouth back to its original color, but only if the mouth is being displayed.