To work out what it means to implement an interface, see one advantage of having interfaces in practice, and try out working with Lists.

In this lab, you’ll be creating a simulation of a garden. Specifically you’ll:

  • Instantiate some plants and put the plants in a List
  • Simulate several days, including some watering of the plants
  • Display the plants


This is a lab assignment that you’ll be handing in on Moodle. You should complete it on Wednesday Jan 13th, but it isn’t due until Friday Jan 15th at 5:00pm Central.

You’ll do this lab on repl.it. Open Garden Lab.

You’re welcome to work on this lab with input from one or more members of your collaborative learning group. You should write all of your own code, but you’re welcome to share your screen/use multiplayer mode with members of your collaborative learning group to look at one another’s code, make suggestions, and compare ideas. Take a look at the Collaboration Policies document on Moodle if you have any questions about what’s permitted.

You’re strongly encouraged to reach out to your group about questions that arise as you’re programming or ideas that come up about design, data structures, Java coding, or anything else.

You’re also (as always) welcome to post questions on Moodle to the whole class. Since this is a lab, you can be more liberal in your posting of code, but please do limit the amount of code you’re posting in order to enable people to help most effectively, and if you’re not sure what part of the code you need help with, come to office hours, lab assistant hours, or post the code privately so only the course staff and I can see it.

You might also check out the common Java Errors and Fixes document, linked on Moodle. You and your classmates will collaboratively add to this document, and if you’re stuck, you might find a helpful suggestion there.

Exercise 0

Using the Add File button on repl.it, add a Collaborations.txt file and describe any interactions you have with your collaborative learning group on this lab. Also note any outside sources such as websites that you referenced.

Exercise 1

a. The files on repl.it include a Plant interface. Read through the interface; you can also take a look at the Javadoc for the interface here.

b. Decide on a kind of Plant you want to implement. Carrot is already taken, so choose something else! Make a file where you’ll implement your Plant:

public class YourPlant implements Plant {
    //stuff goes here

c. Copy over the entire body of the interface including all the method names and the comments.

d. Add the bodies of the methods but have them just do nothing but just returning null or 0 depending on what type they return:

public String getName() {
    return null;

e. Make sure everything compiles:

javac *.java

Exercise 2

a. Fill in all the methods of your Plant class, feel free to get creative with the status of your plant depending on its water!

b. Create an instance of your plant in the main of your plant’s file.

c. Compile and run your plant’s file to make sure everything works and correct any errors.

Exercise 3

Time to make your Garden! a. In the main of Garden.java create a List of Plants (an ArrayList or LinkedList will be fine). You will need to import some libraries to be able to use these data structures.

b. Create at least one Carrot and put it in your list. The Carrot class file is in the starter code though you may not be able to see it. If you want to see that it’s there, type ls in the terminal prompt and you’ll see all the .class files.

c. Create at least one of your own plant type and put it in your list.

d. Create a for loop that simulates several days time elapsing, during which you should probably water your plants as well (remember you should be compiling and running your code every time you add something)

e. Display the plants in the garden at the end of main.

Exercise 4

In a comment in the main of Garden, reflect on the benefit of having an interface for Plant when creating your garden simulation.


Download your files as a zip, and upload that zip to Moodle under the appropriate assignment.

This activity is not a homework assignment. That means that you’re evaluated on whether you attempted all parts of it, but your work will not be graded for correctness as long as a clear effort has been made. If you aren’t able to complete some parts, great ways to indicate clear effort are to reach out for help before the deadline (note ways you did so in your Collaborations.txt file) and to use comments in the code to indicate things you tried but what went wrong/where you got stuck.


Remember to submit your code for the above requirements first before working on extensions!

Once you get the basic simulation working, there are a number of extensions you can try if you have extra time. Pick one(s) that seem interesting to you or that you’re not quite sure how to do yet:

  • Use object oriented style to complete the full garden simulation (putting more than only two plants in a list, simulating several days and watering of the plants on at least some days, and then displaying all plants). Jot down some notes on paper about how to design Garden. You should have your list of Plants be an instance variable and have methods like addPlant(Plant) and waterAllPlants. Once you’ve written out what you want to include on paper, implement it!
  • Add a method in Garden that takes the name of a plant and waters only plants with that name: water(String plantName).
  • Choose a random amount by which to vary the amount of water (e.g., maybe your sprinkler hits some plants more than others, or maybe the rainfall is lighter/heavier than forecasted). Check out Random or Math.random().
  • Vary the behavior of the Plant you implemented with an additional variable, such as age of the plant.
  • Play with inheritance - e.g., you could have a Tomato abstract class and CherryTomato, HeirloomTomato, etc that extend that class.
  • Read the plants to add from a file. E.g., if you had Tomato and Carrot classes, your file could have lines saying either tomato or carrot. For each line, you add a new plant to the garden of the appropriate type.