Description
In this assignment you will model 3 kinds of cloud: stratus, cumulus, and cirrus.
Stratus clouds Cumulus clouds
Cirrus clouds
Stratus and cumulus clouds can make rain; cirrus clouds cannot.
DUE DATE
This assignment is due on or before 11:59 PM on Tuesday September
12. Late work will not be accepted except in cases of documented
personal emergency.
GETTING STARTED
These instructions assume you’ve become familiar with Eclipse by doing Lab 1 /
Homework 1. If any steps here are confusing, see the illustrations in the Lab 1 /
HW1 instructions.
Create a directory called “HW2Workspace” wherever you choose. Start Eclipse. If it
prompts you to “Select a Workspace”, browse to HW2Workspace. Otherwise, it
might come up in the last workspace you were in; in this case select File -> Switch
Workspace and browse to HW2Workspace.
If you see the Welcome screen below, click the arrow circled in red.
Fig. 1
Use the menu item File -> New Java Project to create a new project. Caution: create a
new Java Project, not a new Project. A wizard will appear. Type “hw2project” for the
project name, and use defaults for all other settings. When you’re finished, the
Package Explorer will display your project.
Click on the tiny right-arrow next to the project name to expand the project. There
isn’t anything in the project yet, so the expansion won’t be dramatic.
Right-click on the “src” icon and select the New->Package menu item; fill in the
wizard form to create a package called “weather”.
Create a class called “Sky” in the weather package as follows: Right-click on the icon
next to “weather” in the Package Explorer and use the New -> Class menu item to
create a class called “Sky” in the weather package.
Create 4 other classes in the weather package: Cloud, StratusCloud, CumulusCloud,
and CirrusCloud. The class names, as well as the package name, must be spelled and
capitalized exactly as shown here, or the automatic tester software will give you
zero points. You already know the capitalization convention for class names. The
convention for package names, which you must always follow in 46B, is alllowercase.
The large panel in the center of Eclipse now lets you edit your source files. Note that
the first line of each source says “package weather;”. When a source file is in a
package, this package declaration line must be the first thing in the file.
Now you’re ready to write a polymorphic model. Fill in the bodies of all the classes
as described below. When everything is running, you will create one last class, called
Sky2, that will be a cleaner implementation of Sky.
Cloud.java
This class needs:
1) Private float instance variables: bottom and top.
2) A ctor that takes bottom and top as args and stores them in the instance
variables. NOTE: “ctor” is an abbreviation for “constructor”.
3) A public method getHeight() that returns a float, whose value is top minus
bottom.
4) A public String method rain() that returns “It is raining”
StratusCloud.java and CumulusCloud.java
For these classes:
1) Change the class declarations so that they are subclasses of Cloud.
2) Fix the ctors so that they pass bottom and top to the superclass ctor.
CirrusCloud.java
Subclasses of Cloud inherit a rain() method that is not appropriate for cirrus clouds.
Override rain() so that it returns “I cannot make rain”
Sky.java
This class holds lots of cloud instances of various types, and computes the average
cloud height. It needs:
1) A private ArrayList called clouds.
2) A ctor that creates the clouds array list with an initial capacity of 100. Look up
the javadoc API page for ArrayList to see what ArrayList ctor to call. If you don’t
know how to do this, ask on Piazza. DON’T ask Piazza for the answer, just ask
how to find the javadoc API page.
3) A public method called add(Cloud c) that takes a cloud and adds it to the array
list. The return type of this method should be boolean, and the method should
always return true. That’s a little weird but it will make more sense later.
4) A public float method called getMeanHeight(), which returns the average height
of all the clouds in the array list.
5) A main() method. Paste in the following:
public static void main(String[] args)
{
StratusCloud strat = new StratusCloud(100, 1000);
if (!strat.rain().startsWith(“It is raining”))
System.out.println(“Bad StratusCloud::rain”);
CumulusCloud cumu = new CumulusCloud(200, 2000);
if (!cumu.rain().startsWith(“It is raining”))
System.out.println(“Bad CumulusCloud::rain”);
CirrusCloud cirr = new CirrusCloud(300, 3000);
if (!cirr.rain().startsWith(“I cannot make”))
System.out.println(“Bad CirrusCloud::rain”);
Sky sky = new Sky();
sky.add(strat);
sky.add(cumu);
sky.add(cirr);
float mean = sky.getMeanHeight();
if (mean < 1799 || mean > 1801)
System.out.println(“Bad mean height: expected 1800, saw ” + mean);
System.out.println(“Everything (else) is ok”);
}
To test your work so far, run Sky as an application. Click the tiny “Run” button at the
top of Eclipse (a white triangle pointing right, inside a green circle). The only output
should be “Everything (else) is ok”.
Sky2.java
Lastly, implement Sky in a somewhat different way. When one class holds many
references to instances of another class, we say (for example) that Sky “aggregates”
clouds. Sky aggregates by owning an array list. Sky2 will aggregate by being (in a
sense) an array list. That is, Sky2 will extend ArrayList.
Create class Sky2 in the weather. The Sky2 ctor will need to explicitly call the correct
superclass ctor, so that the initial capacity is 100.
Copy getMeanHeight() from Sky. You need to change it so that it traverses the
correct list of clouds, which is the instance of Sky2 that is executing
getMeanHeight(). Huge hint: its name is “this”.
What about adding clouds to Sky2? You could just copy add() from Sky and then
make a simple change. But there is an even simpler way.
Paste in the main() method from the Sky class. Change the line “Sky sky = new
Sky()” to “Sky2 sky = new Sky2()” To test Sky2, run it as an application.
Testing your work
Import WeatherTester.java, which you downloaded along with this document. The
easiest way to do this is to just drag-and-drop it into the “weather” package in the
Package Explorer. Run WeatherTester as an app. For this assignment, nothing works
unless almost everything works, so there isn’t any partial credit. You’ll either get
100 points or 0 points. If you get 0 points the tester will tell you exactly what the
problem is, so you can fix your bug and get 100.
SUBMISSION
Export your work as a jar file called “CS46BHW2.jar”. Follow the same procedure
that you used in Lab 1. Check the contents of your jar; if you upload the wrong jar, or
a jar that doesn’t contain all the java sources, you’ll get zero points for this
homework.
When you’re satisfied, upload CS46BHW2.jar to Canvas.
