CPSC 170 Lab 2
Array Lists, Inheritance, and Mouse Listeners

As usual, create a lab2 subdirectory for today's lab, open this document in Firefox, and start Eclipse.


The file Card.java conatains a basic representation of a playing card. The file PileOfCards.java contains the stub code for a class that manages collection of cards. This is very similar to last week's CDCollection. The major difference is that you will be implementing pileofCards using an ArrayList instead of an array. This means that you don't have to worry (too much) about managing the way the collection is stored (are you ever going to go "outOfBounds"?). Instead you are just going to use the predefined interface of the arraylist to help manage the data for you.
  1. The code has been commented in Javadoc style. Generate the javadoc for the PileOfCards code to generate the html description of the class. Study the HTML file and make not of the following:

  2. Implement the pileOfCards class according to the specifications in its JavaDoc.

  3. If you have thought about it correctly, you should be confident that pileOfCards is free of logic and run-time errors. If you are not confident, take a few moments to think about where you may have gone wrong and convince yourself that it is correct. Make any changes that you feel are necessary.

  4. If you skipped over step 3, because there was nothing to type, you'll regret it in the long run - I'm serious - stop and think about your code for a second.

  5. When you are confident that your code is correct, write a text-based driver program to verifies that your pileOfCards code works correctly. (Make sure that your this program will convince me! P.S. there is nothing "random" about this program). The output of your program should include statements or what condition is being checked, the anticipated outcome of this statement and the actual outcome of this statement. Observe: It is not acceptable for the PileOfCards class to generate any run-time errors - all "bad" conditions should be gracefully dealt with.

  6. Write a graphical driver program that interacts with a pile of cards. The file CardGame.java contains a simple stub for a JFrame that contains a CardPanel (which is-a JPanel). You will need to update the CardPanel class with the following changes:


When one class is derived from another, we know that the child class can refer to the parent class using a special identifier ________________________;

In essence we are saying, "do what the parent does.... plus a little more".

We often see this used with constructors - the initial configuration is the same as the parent, but we also are concerned about initializing data that is unique to the child class. Since this is such a common occurrence, the constructor for a child class implicitly invokes the parent's constructor if there is not an explicit call to the constructor.. To see this in action, download ClassA.java, ClassB.java and ABInherit.java After looking at the code, compile and execute ABInherit.java - Does it do what you expected?

Inheritance with methods

File Dog.java contains a declaration for a Dog class. Save this file to your directory and study it -- notice what instance variables and methods are provided.

File DogTest.java contains a simple driver program that creates a dog and makes it speak. Study DogTest.java, save it to your directory, and then run it to confirm what it does.

The file Yorkshire.java contain declarations for a class that extend Dog. Save and study this files as well. Modify DogTest.java to add statements to add and print a Yorkshire (also make it speak).

The file Labrador.java also extends the Dog class. However, note that the Labrador constructor takes two parameters: the name and color of the labrador, both strings. Notice that this class contains an error:

Implicit super constructor Dog() is undefined
What's going on? Hint: Think about what happened in the previous activity regarding constructors and subclasses. Fix the problem and then modify DogTest.java to create and make the Dog, Labrador, and Yorkshire all speak.

Add code to DogTest.java to print the average breed weight for both your Labrador and your Yorkshire. Use the avgBreedWeight() method for both. Look at the error that you get. Figure out what is wrong and fix the problem by adding the needed code to the Yorkshire class.

Print DogTest.java, Dog.java, Labrador.java, and Yorkshire.java to turn in.

Mouse Events

Programs can also respond to mouse events -- moving and clicking the mouse -- that are not tied to any particular GUI component. Java divides these into two categories: mouse events and mouse motion events. A MouseListener (a class that implements the MouseListener interface) must provide bodies for methods corresponding to each of the mouse events. A MouseMotionListener (implementing the MouseMotionListener interface) must provide bodies for methods corresponding to each of the mouse motion events. These events are described in section 7.9 of the text.

  1. File MousePlay.java contains a program that displays a message saying when the mouse button is pressed and released. It uses MousePlayPanel.java to define the JPanel that is actually displayed. Save these files to your directory, open them in Eclipse, and run MousePlay to see how it works. Note that MousePlayPanel has an inner class MousePlayListener that implements MouseListener by giving bodies for the five MouseListener methods. Even though nothing is done when the mouse is clicked or when it enters or exits, those methods still appear with empty bodies -- this is required for the MouseListener interface to be implemented.

    Modify MousePlayPanel so that it also prints appropriate messages when the mouse is clicked, when it enters the panel, and when it exits. Play with the resulting program until you understand how the mouse events are generated.

  2. Files Dots.java and DotsPanel.java contain revised versions of the code in listings 7.18 and 7.19 in the text. Dots draws a dot every time the uses presses the mouse button; only the current dot is shown in the revised version. Save these files to your directory and run Dots to see how it works. Then modify DotsPanel as follows:
    1. Make the dots that appear alternately red and green. To do this, you will need to make the following changes:
      • Add an instance variable to hold the dot color.
      • Add an instance variable to count the number of dots that have been drawn.
      • When the mouse is pressed, in addition to setting the draw point you need to update the counter and change the dot color to green if the counter is odd, to red if it is even. Then call repaint.
    2. Modify your code so that the dot is drawn where the mouse is released, not where it is pressed.

    Print DotsPanel.java to turn in.

    HAND IN: