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Create a new Eclipse workspace named "Lab6_1234567890" on the desktop of your computer (replace
1234567890 with your student ID number). For each question below, create a new project in that workspace. Call
each project by its question number: "Question1", "Question2", etc. If you do not remember how to create a
workspace or projects, read the "Introduction to Eclipse" document which is on iSpace. Answer all the questions below.
At the end of the lab, create a ZIP archive of the whole workspace folder. The resulting ZIP file must be called
"Lab6_1234567890.zip" (replace 1234567890 with your student ID number). Upload the ZIP file on iSpace.
Question 1
Create a class a class Cat with the following UML diagram:
+-----------------------------------+
| Cat |
+-----------------------------------+
| - name: String |
| - weight: double |
+-----------------------------------+
| + Cat(String name, double weight) |
| + getName(): String |
| + getWeight(): double |
| + feed(): void |
| + testCat(): void |
+-----------------------------------+
Feeding a cat adds 1.0 to its weight.
The testCat method is static and is used for testing the Cat class. Here is the code for this testCat method:
public static void testCat() {
Cat c = new Cat("Meow", 2.0);
System.out.println(c.getName() == "Meow");
System.out.println(c.getWeight() == 2.0);
c.feed();
// The name is still the same but the weight increased by 1.0:
System.out.println(c.getName() == "Meow");
System.out.println(c.getWeight() == 3.0);
}
And here is the Start class to test the Cat class:
public class Start {
public static void main(String[] args) {
Cat.testCat();
}
}
Question 2
Add to your program a class Dog with the following UML diagram:
+-----------------------------------+
| Dog |
+-----------------------------------+
| - name: String |
| - weight: double |
+-----------------------------------+
| + Dog(String name, double weight) |
| + getName(): String |
| + getWeight(): double |
| + feed(): void |
| + testDog(): void |
+-----------------------------------+
Feeding a dog adds 2.0 to its weight.
The testDog method is static and is used for testing the Dog class. Here is the code for this testDog method:
public static void testDog() {
Dog d = new Dog("Woof", 2.0);
System.out.println(d.getName() == "Woof");
System.out.println(d.getWeight() == 2.0);
d.feed();
// The name is still the same but the weight increased by 2.0:
System.out.println(d.getName() == "Woof");
System.out.println(d.getWeight() == 4.0);
}
Do not forget to modify the main method of the Start class to test the new Dog class too!
Question 3
Add a Student class so that a student has a cat as a pet:
+---------------------------------+
| Student |
+---------------------------------+
| - name: String |
| - pet: Cat |
+---------------------------------+
| + Student(String name, Cat pet) |
| + getName(): String |
| + getPet(): Cat |
| + testStudent(): void |
+---------------------------------+
Do not forget to write the testStudent method of the Student class to test the getName and getPet methods,
and to modify the main method of the Start class to test the new Student class too!
Question 4
If you look at the code of the Cat and Dog classes above, you will see that they are almost the same. The only
differences are that:
the names of the classes are different;
the names of the constructors are different (since the names of the classes are different);
the feed methods add a different amount of weight;
the testCat and testDog methods are different (since the names of the classes are different).
Everything else (the name and weight instance variables, the getName and getWeight methods) is the same. This
means that there is a lot of code duplication between the two classes Cat and Dog. Therefore it is a good idea to create
a new class Animal that will contain only one copy of that code, and have the Cat and Dog classes then inherit the
code from the Animal class.
Add a class Animal to the program above, with has the following UML diagram:
+--------------------------------------+
| Animal |
+--------------------------------------+
| - name: String |
| - weight: double |
+--------------------------------------+
| + Animal(String name, double weight) |
| + getName(): String |
| + getWeight(): double |
| + setWeight(double weight): void |
| + testAnimal(): void |
+--------------------------------------+
The Dog and Cat classes should then be derived classes from the Animal base class (in other words, the Dog and Cat
classes should inherit from the Animal class).
Which instance variables, constructors, and methods from the Dog and Cat classes can be moved to the Animal class?
Which instance variables, constructors, and methods of the Dog and Cat classes must stay in these classes? How
should they be modified?
After adding the Animal class, modify the Student class so that the student has an animal as a pet, not a cat.
Do not forget to:
change the main method of the Start class to run the unit tests of the new Animal class;
add new tests to the Student class to test that you can now use an Animal object as the pet of a student;
Now that the Student class uses an animal as pet, can you still use a cat object as the pet of a student? Why or why
not?
Can you now use a dog object as the pet of a student? Why or why not?
Question 5
Add a Bird class to your program. A bird is an animal, therefore your Bird class must be a class derived from the
Animal class. The UML diagram of the Bird class is as follows:
+-----------------------------------------------------+
| Bird |
+-----------------------------------------------------+
| - altitude: double |
+-----------------------------------------------------+
| + Bird(String name, double weight, double altitude) |
| + getAltitude(): double |
| + testBird(): void |
+-----------------------------------------------------+
The altitude instance variable represents the altitude at which the bird is flying. Cats and dogs do not fly so they do
not have an altitude.
The constructor for the Bird class takes three arguments: the name of the bird, the weight of the bird, and the altitude
at which the bird is flying. The altitude argument of the constructor is stored into the altitude instance variable of
the Bird class. Where are the name and weight of the bird stored? How?
Do not forget to:
change the main method of the Start class to run the unit tests of the new Bird class;
add new tests to the Student class to test that you can now use a Bird object as the pet of a student;
Suppose a student has a bird as a pet. Can the student get the altitude of his pet?
Question 6
Add a Chicken class to your program. A chicken is a bird, therefore your Chicken class must be a class derived from
the Bird class. The UML diagram of the Chicken class is as follows:
+-------------------------+
| Chicken |
+-------------------------+
+-------------------------+
| + Chicken(String name) |
| + testChicken(): void |
+-------------------------+
A chicken always has a weight of 5.0 and an altitude of 0.0 (chickens spend all their time on the ground).
Do not forget to:
change the main method of the Start class to run the unit tests of the new Chicken class;
add new tests to the Student class to test that you can now use a Chicken object as the pet of a student;
Question 7
Both the Student class and the Animal class have a name instance variable and a getName method, which leads to
code duplication between these two classes. To solve this problem, add a new LivingThing class to your program,
which becomes the superclass for the Student and Animal classes, and which contains only one copy of the code for
the name instance variable and the getName method. The LivingThing class has the following UML diagram:
+----------------------------+
| LivingThing |
+----------------------------+
| - name: String |
+----------------------------+
| + LivingThing(String name) |
| + getName(): String |
| + testLivingThing(): void |
+----------------------------+
Change the Student class and Animal class so that both classes are now derived from the LivingThing class.
Then remove the name instance variables and the getName methods from the Animal and Student classes. The
other classes do not change.
Check that all your tests still work.
Do not forget to change the main method of the Start class to run the unit tests of the new LivingThing class.
LivingThing is now the top-most class. It has two derived classes: Animal and Student. Animal has three
derived classes: Cat, Dog, and Bird. Bird has one derived class: Chicken. Student, Cat, Dog, and Chicken do
not have derived classes.
Create a new Eclipse workspace named "Lab6_1234567890" on the desktop of your computer (replace
1234567890 with your student ID number). For each question below, create a new project in that workspace. Call
each project by its question number: "Question1", "Question2", etc. If you do not remember how to create a
workspace or projects, read the "Introduction to Eclipse" document which is on iSpace. Answer all the questions below.
At the end of the lab, create a ZIP archive of the whole workspace folder. The resulting ZIP file must be called
"Lab6_1234567890.zip" (replace 1234567890 with your student ID number). Upload the ZIP file on iSpace.
Question 1
Create a class a class Cat with the following UML diagram:
+-----------------------------------+
| Cat |
+-----------------------------------+
| - name: String |
| - weight: double |
+-----------------------------------+
| + Cat(String name, double weight) |
| + getName(): String |
| + getWeight(): double |
| + feed(): void |
| + testCat(): void |
+-----------------------------------+
Feeding a cat adds 1.0 to its weight.
The testCat method is static and is used for testing the Cat class. Here is the code for this testCat method:
public static void testCat() {
Cat c = new Cat("Meow", 2.0);
System.out.println(c.getName() == "Meow");
System.out.println(c.getWeight() == 2.0);
c.feed();
// The name is still the same but the weight increased by 1.0:
System.out.println(c.getName() == "Meow");
System.out.println(c.getWeight() == 3.0);
}
And here is the Start class to test the Cat class:
public class Start {
public static void main(String[] args) {
Cat.testCat();
}
}
Question 2
Add to your program a class Dog with the following UML diagram:
+-----------------------------------+
| Dog |
+-----------------------------------+
| - name: String |
| - weight: double |
+-----------------------------------+
| + Dog(String name, double weight) |
| + getName(): String |
| + getWeight(): double |
| + feed(): void |
| + testDog(): void |
+-----------------------------------+
Feeding a dog adds 2.0 to its weight.
The testDog method is static and is used for testing the Dog class. Here is the code for this testDog method:
public static void testDog() {
Dog d = new Dog("Woof", 2.0);
System.out.println(d.getName() == "Woof");
System.out.println(d.getWeight() == 2.0);
d.feed();
// The name is still the same but the weight increased by 2.0:
System.out.println(d.getName() == "Woof");
System.out.println(d.getWeight() == 4.0);
}
Do not forget to modify the main method of the Start class to test the new Dog class too!
Question 3
Add a Student class so that a student has a cat as a pet:
+---------------------------------+
| Student |
+---------------------------------+
| - name: String |
| - pet: Cat |
+---------------------------------+
| + Student(String name, Cat pet) |
| + getName(): String |
| + getPet(): Cat |
| + testStudent(): void |
+---------------------------------+
Do not forget to write the testStudent method of the Student class to test the getName and getPet methods,
and to modify the main method of the Start class to test the new Student class too!
Question 4
If you look at the code of the Cat and Dog classes above, you will see that they are almost the same. The only
differences are that:
the names of the classes are different;
the names of the constructors are different (since the names of the classes are different);
the feed methods add a different amount of weight;
the testCat and testDog methods are different (since the names of the classes are different).
Everything else (the name and weight instance variables, the getName and getWeight methods) is the same. This
means that there is a lot of code duplication between the two classes Cat and Dog. Therefore it is a good idea to create
a new class Animal that will contain only one copy of that code, and have the Cat and Dog classes then inherit the
code from the Animal class.
Add a class Animal to the program above, with has the following UML diagram:
+--------------------------------------+
| Animal |
+--------------------------------------+
| - name: String |
| - weight: double |
+--------------------------------------+
| + Animal(String name, double weight) |
| + getName(): String |
| + getWeight(): double |
| + setWeight(double weight): void |
| + testAnimal(): void |
+--------------------------------------+
The Dog and Cat classes should then be derived classes from the Animal base class (in other words, the Dog and Cat
classes should inherit from the Animal class).
Which instance variables, constructors, and methods from the Dog and Cat classes can be moved to the Animal class?
Which instance variables, constructors, and methods of the Dog and Cat classes must stay in these classes? How
should they be modified?
After adding the Animal class, modify the Student class so that the student has an animal as a pet, not a cat.
Do not forget to:
change the main method of the Start class to run the unit tests of the new Animal class;
add new tests to the Student class to test that you can now use an Animal object as the pet of a student;
Now that the Student class uses an animal as pet, can you still use a cat object as the pet of a student? Why or why
not?
Can you now use a dog object as the pet of a student? Why or why not?
Question 5
Add a Bird class to your program. A bird is an animal, therefore your Bird class must be a class derived from the
Animal class. The UML diagram of the Bird class is as follows:
+-----------------------------------------------------+
| Bird |
+-----------------------------------------------------+
| - altitude: double |
+-----------------------------------------------------+
| + Bird(String name, double weight, double altitude) |
| + getAltitude(): double |
| + testBird(): void |
+-----------------------------------------------------+
The altitude instance variable represents the altitude at which the bird is flying. Cats and dogs do not fly so they do
not have an altitude.
The constructor for the Bird class takes three arguments: the name of the bird, the weight of the bird, and the altitude
at which the bird is flying. The altitude argument of the constructor is stored into the altitude instance variable of
the Bird class. Where are the name and weight of the bird stored? How?
Do not forget to:
change the main method of the Start class to run the unit tests of the new Bird class;
add new tests to the Student class to test that you can now use a Bird object as the pet of a student;
Suppose a student has a bird as a pet. Can the student get the altitude of his pet?
Question 6
Add a Chicken class to your program. A chicken is a bird, therefore your Chicken class must be a class derived from
the Bird class. The UML diagram of the Chicken class is as follows:
+-------------------------+
| Chicken |
+-------------------------+
+-------------------------+
| + Chicken(String name) |
| + testChicken(): void |
+-------------------------+
A chicken always has a weight of 5.0 and an altitude of 0.0 (chickens spend all their time on the ground).
Do not forget to:
change the main method of the Start class to run the unit tests of the new Chicken class;
add new tests to the Student class to test that you can now use a Chicken object as the pet of a student;
Question 7
Both the Student class and the Animal class have a name instance variable and a getName method, which leads to
code duplication between these two classes. To solve this problem, add a new LivingThing class to your program,
which becomes the superclass for the Student and Animal classes, and which contains only one copy of the code for
the name instance variable and the getName method. The LivingThing class has the following UML diagram:
+----------------------------+
| LivingThing |
+----------------------------+
| - name: String |
+----------------------------+
| + LivingThing(String name) |
| + getName(): String |
| + testLivingThing(): void |
+----------------------------+
Change the Student class and Animal class so that both classes are now derived from the LivingThing class.
Then remove the name instance variables and the getName methods from the Animal and Student classes. The
other classes do not change.
Check that all your tests still work.
Do not forget to change the main method of the Start class to run the unit tests of the new LivingThing class.
LivingThing is now the top-most class. It has two derived classes: Animal and Student. Animal has three
derived classes: Cat, Dog, and Bird. Bird has one derived class: Chicken. Student, Cat, Dog, and Chicken do
not have derived classes.