lab5

lab/lab5/Question1/Cat.java

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+/*
+ * Author: CHEN Yongyuan (Walter) 1930006025 from OOP(1007)
+ * Date: 2022-03-19
+ * Description: Cat class
+ */
+
+public class Cat {
+	/**
+	 * Cat's name
+	 */
+	private String name;
+
+	/**
+	 * Cat's weight
+	 */
+	private double weight;
+
+	/**
+	 * Constructor. Initialize the name and weight of the cat
+	 */
+	public Cat(String name, double weight) {
+		this.name = name;
+		this.weight = weight;
+	}
+
+	/**
+	 * Get the name of the cat
+	 *
+	 * @return name of the cat
+	 */
+	public String getName() {
+		return name;
+	}
+
+	/**
+	 * Get the weight of the cat
+	 *
+	 * @return weight of the cat
+	 */
+	public double getWeight() {
+		return weight;
+	}
+
+	/**
+	 * Feeding a cat adds 1.0 to its weight
+	 */
+	public void feed() {
+		weight += 1.0;
+	}
+
+	/**
+	 * Test
+	 */
+	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);
+	}
+}

lab/lab5/Question1/Start.java

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+public class Start {
+	public static void main(String[] args) {
+		Cat.testCat();
+	}
+}

lab/lab5/Question2/Cat.java

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+/*
+ * Author: CHEN Yongyuan (Walter) 1930006025 from OOP(1007)
+ * Date: 2022-03-19
+ * Description: Cat class
+ */
+
+public class Cat {
+	/**
+	 * Cat's name
+	 */
+	private String name;
+
+	/**
+	 * Cat's weight
+	 */
+	private double weight;
+
+	/**
+	 * Constructor. Initialize the name and weight of the cat
+	 */
+	public Cat(String name, double weight) {
+		this.name = name;
+		this.weight = weight;
+	}
+
+	/**
+	 * Get the name of the cat
+	 *
+	 * @return name of the cat
+	 */
+	public String getName() {
+		return name;
+	}
+
+	/**
+	 * Get the weight of the cat
+	 *
+	 * @return weight of the cat
+	 */
+	public double getWeight() {
+		return weight;
+	}
+
+	/**
+	 * Feeding a cat adds 1.0 to its weight
+	 */
+	public void feed() {
+		weight += 1.0;
+	}
+
+	/**
+	 * Test
+	 */
+	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);
+	}
+}

lab/lab5/Question2/Dog.java

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+/*
+ * Author: CHEN Yongyuan (Walter) 1930006025 from OOP(1007)
+ * Date: 2022-03-19
+ * Description: Dog class
+ */
+
+public class Dog {
+	/**
+	 * Dog's name
+	 */
+	private String name;
+
+	/**
+	 * Dog's weight
+	 */
+	private double weight;
+
+	/**
+	 * Constructor. Initialize the name and weight of the dog
+	 */
+	public Dog(String name, double weight) {
+		this.name = name;
+		this.weight = weight;
+	}
+
+	/**
+	 * Get the name of the dog
+	 *
+	 * @return name of the dog
+	 */
+	public String getName() {
+		return name;
+	}
+
+	/**
+	 * Get the weight of the dog
+	 *
+	 * @return weight of the dog
+	 */
+	public double getWeight() {
+		return weight;
+	}
+
+	/**
+	 * Feeding a dog adds 2.0 to its weight
+	 */
+	public void feed() {
+		weight += 2.0;
+	}
+
+	/**
+	 * Test
+	 */
+	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);
+	}
+}

lab/lab5/Question2/Start.java

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+public class Start {
+	public static void main(String[] args) {
+		Cat.testCat();
+		Dog.testDog();
+	}
+}

lab/lab5/Question3/Cat.java

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+/*
+ * Author: CHEN Yongyuan (Walter) 1930006025 from OOP(1007)
+ * Date: 2022-03-19
+ * Description: Cat class
+ */
+
+public class Cat {
+	/**
+	 * Cat's name
+	 */
+	private String name;
+
+	/**
+	 * Cat's weight
+	 */
+	private double weight;
+
+	/**
+	 * Constructor. Initialize the name and weight of the cat
+	 */
+	public Cat(String name, double weight) {
+		this.name = name;
+		this.weight = weight;
+	}
+
+	/**
+	 * Get the name of the cat
+	 *
+	 * @return name of the cat
+	 */
+	public String getName() {
+		return name;
+	}
+
+	/**
+	 * Get the weight of the cat
+	 *
+	 * @return weight of the cat
+	 */
+	public double getWeight() {
+		return weight;
+	}
+
+	/**
+	 * Feeding a cat adds 1.0 to its weight
+	 */
+	public void feed() {
+		weight += 1.0;
+	}
+
+	/**
+	 * Test
+	 */
+	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);
+	}
+}

lab/lab5/Question3/Dog.java

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+/*
+ * Author: CHEN Yongyuan (Walter) 1930006025 from OOP(1007)
+ * Date: 2022-03-19
+ * Description: Dog class
+ */
+
+public class Dog {
+	/**
+	 * Dog's name
+	 */
+	private String name;
+
+	/**
+	 * Dog's weight
+	 */
+	private double weight;
+
+	/**
+	 * Constructor. Initialize the name and weight of the dog
+	 */
+	public Dog(String name, double weight) {
+		this.name = name;
+		this.weight = weight;
+	}
+
+	/**
+	 * Get the name of the dog
+	 *
+	 * @return name of the dog
+	 */
+	public String getName() {
+		return name;
+	}
+
+	/**
+	 * Get the weight of the dog
+	 *
+	 * @return weight of the dog
+	 */
+	public double getWeight() {
+		return weight;
+	}
+
+	/**
+	 * Feeding a dog adds 2.0 to its weight
+	 */
+	public void feed() {
+		weight += 2.0;
+	}
+
+	/**
+	 * Test
+	 */
+	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);
+	}
+}

lab/lab5/Question3/Start.java

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+public class Start {
+	public static void main(String[] args) {
+		Cat.testCat();
+		Dog.testDog();
+		Student.testStudent();
+	}
+}

lab/lab5/Question3/Student.java

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+/*
+ * Author: CHEN Yongyuan (Walter) 1930006025 from OOP(1007)
+ * Date: 2022/03/19
+ * Description: Student class
+ */
+
+public class Student {
+	/**
+	 * Student's name
+	 */
+	private String name;
+
+	/**
+	 * Student's pet
+	 */
+	private Cat pet;
+
+	/**
+	 * Constructor
+	 */
+	public Student(String name, Cat pet) {
+		this.name = name;
+		this.pet = pet;
+	}
+
+	/**
+	 * Getter for name
+	 *
+	 * @return String
+	 */
+	public String getName() {
+		return name;
+	}
+
+	/**
+	 * Getter for pet
+	 *
+	 * @return Cat
+	 */
+	public Cat getPet() {
+		return pet;
+	}
+
+	/**
+	 * Test
+	 */
+	public static void testStudent() {
+		Cat cat = new Cat("Tom", 1.0);
+		Student student = new Student("Walter", cat);
+		System.out.println(student.getName() == "Walter");
+		System.out.println(student.getPet() == cat);
+		System.out.println(student.getPet().getName() == "Tom");
+		System.out.println(student.getPet().getWeight() == 1.0);
+	}
+
+}

lab/lab5/Question4/Animal.java

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+/*
+ * Author: CHEN Yongyuan (Walter) 1930006025 from OOP(1007)
+ * Date: 2022/03/19
+ * Description: This is the class of Animal.
+ */
+
+public class Animal {
+	/**
+	 * Animal's name
+	 */
+	private String name;
+
+	/**
+	 * Animal's weight
+	 */
+	private double weight;
+
+	/**
+	 * Constructor. Initialize the name and weight of the animal.
+	 */
+	public Animal(String name, double weight) {
+		this.name = name;
+		this.weight = weight;
+	}
+
+	/**
+	 * Get the name of the animal.
+	 * 
+	 * @return the name of the animal
+	 */
+	public String getName() {
+		return name;
+	}
+
+	/**
+	 * Get the weight of the animal.
+	 * 
+	 * @return the weight of the animal
+	 */
+	public double getWeight() {
+		return weight;
+	}
+
+	/**
+	 * Set the weight of the animal.
+	 * 
+	 * @param weight
+	 *            the weight of the animal
+	 */
+	public void setWeight(double weight) {
+		this.weight = weight;
+	}
+
+	/**
+	 * Test
+	 */
+	public static void testAnimal() {
+		Animal animal = new Animal("cat", 1.0);
+		System.out.println(animal.getName() == "cat");
+		System.out.println(animal.getWeight() == 1.0);
+		animal.setWeight(2.0);
+		System.out.println(animal.getName() == "cat");
+		System.out.println(animal.getWeight() == 2.0);
+	}
+}
+

lab/lab5/Question4/Cat.java

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+/*
+ * Author: CHEN Yongyuan (Walter) 1930006025 from OOP(1007)
+ * Date: 2022-03-19
+ * Description: Cat class
+ */
+
+public class Cat extends Animal {
+	/**
+	 * Constructor. Initialize the name and weight of the cat
+	 */
+	public Cat(String name, double weight) {
+		super(name, weight);
+	}
+
+	/**
+	 * Feeding a cat adds 1.0 to its weight
+	 */
+	public void feed() {
+		setWeight(getWeight() + 1.0);
+	}
+
+	/**
+	 * Test
+	 */
+	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);
+	}
+}

lab/lab5/Question4/Dog.java

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+/*
+ * Author: CHEN Yongyuan (Walter) 1930006025 from OOP(1007)
+ * Date: 2022-03-19
+ * Description: Dog class
+ */
+
+public class Dog extends Animal {
+	/**
+	 * Constructor. Initialize the name and weight of the dog
+	 */
+	public Dog(String name, double weight) {
+		super(name, weight);
+	}
+
+	/**
+	 * Feeding a dog adds 2.0 to its weight
+	 */
+	public void feed() {
+		setWeight(getWeight() + 2.0);
+	}
+
+	/**
+	 * Test
+	 */
+	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);
+	}
+}

lab/lab5/Question4/Start.java

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+/**
+ * Answer to question.
+ *
+ * # Question 4
+ *
+ * Q: 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?
+ *
+ * A: Yes, you can. The Student class has a method getPet() that returns the pet
+ * which is Animal type.
+ *
+ * Q: Can you now use a dog object as the pet of a student? Why or why not?
+ *
+ * A: Yes, you can. But only attributes and methods definded in the Animal class
+ * can be accessed. When you do so, the Dog object will be converted to an
+ * Animal object. Assign a child object to a parent object is called upcasting
+ * in Java. Upcasting is implicit.
+ *
+ */
+public class Start {
+	public static void main(String[] args) {
+		Cat.testCat();
+		Dog.testDog();
+		Student.testStudent();
+		Animal.testAnimal();
+	}
+}

lab/lab5/Question4/Student.java

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+/*
+ * Author: CHEN Yongyuan (Walter) 1930006025 from OOP(1007)
+ * Date: 2022/03/19
+ * Description: Student class
+ */
+
+public class Student {
+	/**
+	 * Student's name
+	 */
+	private String name;
+
+	/**
+	 * Student's pet
+	 */
+	private Animal pet;
+
+	/**
+	 * Constructor
+	 */
+	public Student(String name, Animal pet) {
+		this.name = name;
+		this.pet = pet;
+	}
+
+	/**
+	 * Getter for name
+	 *
+	 * @return String
+	 */
+	public String getName() {
+		return name;
+	}
+
+	/**
+	 * Getter for pet
+	 *
+	 * @return Animal
+	 */
+	public Animal getPet() {
+		return pet;
+	}
+
+	/**
+	 * Test
+	 */
+	public static void testStudent() {
+		Cat pet = new Cat("Tom", 1.0);
+		Student student = new Student("Walter", pet);
+		System.out.println(student.getName() == "Walter");
+		System.out.println(student.getPet() == pet);
+		System.out.println(student.getPet().getName() == "Tom");
+		System.out.println(student.getPet().getWeight() == 1.0);
+
+		Dog pet2 = new Dog("Jerry", 1.0);
+		Student student2 = new Student("Walter", pet2);
+		System.out.println(student2.getName() == "Walter");
+		System.out.println(student2.getPet() == pet2);
+		System.out.println(student2.getPet().getName() == "Jerry");
+		System.out.println(student2.getPet().getWeight() == 1.0);
+
+		Animal pet3 = new Animal("Unknown animal", 4.0);
+		Student student3 = new Student("Walter", pet3);
+		System.out.println(student3.getName() == "Walter");
+		System.out.println(student3.getPet() == pet3);
+		System.out.println(student3.getPet().getName() == "Unknown animal");
+		System.out.println(student3.getPet().getWeight() == 4.0);
+	}
+}

lab/lab5/Question5/Animal.java

@@ -0,0 +1,66 @@
+/*
+ * Author: CHEN Yongyuan (Walter) 1930006025 from OOP(1007)
+ * Date: 2022/03/19
+ * Description: This is the class of Animal.
+ */
+
+public class Animal {
+	/**
+	 * Animal's name
+	 */
+	private String name;
+
+	/**
+	 * Animal's weight
+	 */
+	private double weight;
+
+	/**
+	 * Constructor. Initialize the name and weight of the animal.
+	 */
+	public Animal(String name, double weight) {
+		this.name = name;
+		this.weight = weight;
+	}
+
+	/**
+	 * Get the name of the animal.
+	 * 
+	 * @return the name of the animal
+	 */
+	public String getName() {
+		return name;
+	}
+
+	/**
+	 * Get the weight of the animal.
+	 * 
+	 * @return the weight of the animal
+	 */
+	public double getWeight() {
+		return weight;
+	}
+
+	/**
+	 * Set the weight of the animal.
+	 * 
+	 * @param weight
+	 *            the weight of the animal
+	 */
+	public void setWeight(double weight) {
+		this.weight = weight;
+	}
+
+	/**
+	 * Test
+	 */
+	public static void testAnimal() {
+		Animal animal = new Animal("cat", 1.0);
+		System.out.println(animal.getName() == "cat");
+		System.out.println(animal.getWeight() == 1.0);
+		animal.setWeight(2.0);
+		System.out.println(animal.getName() == "cat");
+		System.out.println(animal.getWeight() == 2.0);
+	}
+}
+

lab/lab5/Question5/Bird.java

@@ -0,0 +1,43 @@
+/*
+ * Author: CHEN Yongyuan (Walter) 1930006025 from OOP(1007)
+ * Date: 2022-03-19
+ * Description: This is the class of Bird.
+ */
+
+public class Bird extends Animal {
+	/**
+	 * Altitude of the bird.
+	 */
+	private double altitude;
+
+	/**
+	 * Constructor of Bird.
+	 * 
+	 * @param name     name of the bird
+	 * @param weight   weight of the bird
+	 * @param altitude altitude of the bird
+	 */
+	public Bird(String name, double weight, double altitude) {
+		super(name, weight);
+		this.altitude = altitude;
+	}
+
+	/**
+	 * Get the altitude of the bird.
+	 * 
+	 * @return altitude of the bird
+	 */
+	public double getAltitude() {
+		return altitude;
+	}
+
+	/**
+	 * Test
+	 */
+	public static void testBird() {
+		Bird bird = new Bird("Bird", 1.0, 10.0);
+		System.out.println(bird.getName() == "Bird");
+		System.out.println(bird.getWeight() == 1.0);
+		System.out.println(bird.getAltitude() == 10.0);
+	}
+}

lab/lab5/Question5/Cat.java

@@ -0,0 +1,35 @@
+/*
+ * Author: CHEN Yongyuan (Walter) 1930006025 from OOP(1007)
+ * Date: 2022-03-19
+ * Description: Cat class
+ */
+
+public class Cat extends Animal {
+	/**
+	 * Constructor. Initialize the name and weight of the cat
+	 */
+	public Cat(String name, double weight) {
+		super(name, weight);
+	}
+
+	/**
+	 * Feeding a cat adds 1.0 to its weight
+	 */
+	public void feed() {
+		setWeight(getWeight() + 1.0);
+	}
+
+	/**
+	 * Test
+	 */
+	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);
+	}
+}

lab/lab5/Question5/Dog.java

@@ -0,0 +1,34 @@
+/*
+ * Author: CHEN Yongyuan (Walter) 1930006025 from OOP(1007)
+ * Date: 2022-03-19
+ * Description: Dog class
+ */
+
+public class Dog extends Animal {
+	/**
+	 * Constructor. Initialize the name and weight of the dog
+	 */
+	public Dog(String name, double weight) {
+		super(name, weight);
+	}
+
+	/**
+	 * Feeding a dog adds 2.0 to its weight
+	 */
+	public void feed() {
+		setWeight(getWeight() + 2.0);
+	}
+
+	/**
+	 * Test
+	 */
+	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);
+	}
+}

lab/lab5/Question5/Start.java

@@ -0,0 +1,43 @@
+/**
+ * Answer to question.
+ *
+ * # Question 4
+ *
+ * Q: 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?
+ *
+ * A: Yes, you can. The Student class has a method getPet() that returns the pet
+ * which is Animal type.
+ *
+ * Q: Can you now use a dog object as the pet of a student? Why or why not?
+ *
+ * A: Yes, you can. But only attributes and methods definded in the Animal class
+ * can be accessed. When you do so, the Dog object will be converted to an
+ * Animal object. Assign a child object to a parent object is called upcasting
+ * in Java. Upcasting is implicit.
+ *
+ * # Question 5
+ *
+ * Q: Where are the name and weight of the bird stored? How?
+ *
+ * A: The Bird class has a private instance variable name and weight which are
+ * inherited from the Animal class.
+ *
+ * Q: Suppose a student has a bird as a pet. Can the student get the altitude of
+ * his pet?
+ *
+ * A: No. The student's pet is an Animal object. The Bird object is a subclass
+ * of Animal. getAltitude is only avaliable in Animal object. When we assign a
+ * Bird to an Animal variable, upcasting happend and only attributes and methods
+ * in the super class can be accessed.
+ *
+ */
+public class Start {
+	public static void main(String[] args) {
+		Cat.testCat();
+		Dog.testDog();
+		Student.testStudent();
+		Animal.testAnimal();
+		Bird.testBird();
+	}
+}

lab/lab5/Question5/Student.java

@@ -0,0 +1,76 @@
+/*
+ * Author: CHEN Yongyuan (Walter) 1930006025 from OOP(1007)
+ * Date: 2022/03/19
+ * Description: Student class
+ */
+
+public class Student {
+	/**
+	 * Student's name
+	 */
+	private String name;
+
+	/**
+	 * Student's pet
+	 */
+	private Animal pet;
+
+	/**
+	 * Constructor
+	 */
+	public Student(String name, Animal pet) {
+		this.name = name;
+		this.pet = pet;
+	}
+
+	/**
+	 * Getter for name
+	 *
+	 * @return String
+	 */
+	public String getName() {
+		return name;
+	}
+
+	/**
+	 * Getter for pet
+	 *
+	 * @return Animal
+	 */
+	public Animal getPet() {
+		return pet;
+	}
+
+	/**
+	 * Test
+	 */
+	public static void testStudent() {
+		Cat pet = new Cat("Tom", 1.0);
+		Student student = new Student("Walter", pet);
+		System.out.println(student.getName() == "Walter");
+		System.out.println(student.getPet() == pet);
+		System.out.println(student.getPet().getName() == "Tom");
+		System.out.println(student.getPet().getWeight() == 1.0);
+
+		Dog pet2 = new Dog("Jerry", 1.0);
+		Student student2 = new Student("Walter", pet2);
+		System.out.println(student2.getName() == "Walter");
+		System.out.println(student2.getPet() == pet2);
+		System.out.println(student2.getPet().getName() == "Jerry");
+		System.out.println(student2.getPet().getWeight() == 1.0);
+
+		Animal pet3 = new Animal("Unknown animal", 4.0);
+		Student student3 = new Student("Walter", pet3);
+		System.out.println(student3.getName() == "Walter");
+		System.out.println(student3.getPet() == pet3);
+		System.out.println(student3.getPet().getName() == "Unknown animal");
+		System.out.println(student3.getPet().getWeight() == 4.0);
+
+		Bird pet4 = new Bird("bird", 1.0, 39.0);
+		Student student4 = new Student("Walter", pet4);
+		System.out.println(student4.getName() == "Walter");
+		System.out.println(student4.getPet() == pet4);
+		System.out.println(student4.getPet().getName() == "bird");
+		System.out.println(student4.getPet().getWeight() == 1.0);
+	}
+}

lab/lab5/Question6/Animal.java

@@ -0,0 +1,66 @@
+/*
+ * Author: CHEN Yongyuan (Walter) 1930006025 from OOP(1007)
+ * Date: 2022/03/19
+ * Description: This is the class of Animal.
+ */
+
+public class Animal {
+	/**
+	 * Animal's name
+	 */
+	private String name;
+
+	/**
+	 * Animal's weight
+	 */
+	private double weight;
+
+	/**
+	 * Constructor. Initialize the name and weight of the animal.
+	 */
+	public Animal(String name, double weight) {
+		this.name = name;
+		this.weight = weight;
+	}
+
+	/**
+	 * Get the name of the animal.
+	 * 
+	 * @return the name of the animal
+	 */
+	public String getName() {
+		return name;
+	}
+
+	/**
+	 * Get the weight of the animal.
+	 * 
+	 * @return the weight of the animal
+	 */
+	public double getWeight() {
+		return weight;
+	}
+
+	/**
+	 * Set the weight of the animal.
+	 * 
+	 * @param weight
+	 *            the weight of the animal
+	 */
+	public void setWeight(double weight) {
+		this.weight = weight;
+	}
+
+	/**
+	 * Test
+	 */
+	public static void testAnimal() {
+		Animal animal = new Animal("cat", 1.0);
+		System.out.println(animal.getName() == "cat");
+		System.out.println(animal.getWeight() == 1.0);
+		animal.setWeight(2.0);
+		System.out.println(animal.getName() == "cat");
+		System.out.println(animal.getWeight() == 2.0);
+	}
+}
+

lab/lab5/Question6/Bird.java

@@ -0,0 +1,43 @@
+/*
+ * Author: CHEN Yongyuan (Walter) 1930006025 from OOP(1007)
+ * Date: 2022-03-19
+ * Description: This is the class of Bird.
+ */
+
+public class Bird extends Animal {
+	/**
+	 * Altitude of the bird.
+	 */
+	private double altitude;
+
+	/**
+	 * Constructor of Bird.
+	 * 
+	 * @param name     name of the bird
+	 * @param weight   weight of the bird
+	 * @param altitude altitude of the bird
+	 */
+	public Bird(String name, double weight, double altitude) {
+		super(name, weight);
+		this.altitude = altitude;
+	}
+
+	/**
+	 * Get the altitude of the bird.
+	 * 
+	 * @return altitude of the bird
+	 */
+	public double getAltitude() {
+		return altitude;
+	}
+
+	/**
+	 * Test
+	 */
+	public static void testBird() {
+		Bird bird = new Bird("Bird", 1.0, 10.0);
+		System.out.println(bird.getName() == "Bird");
+		System.out.println(bird.getWeight() == 1.0);
+		System.out.println(bird.getAltitude() == 10.0);
+	}
+}

lab/lab5/Question6/Cat.java

@@ -0,0 +1,35 @@
+/*
+ * Author: CHEN Yongyuan (Walter) 1930006025 from OOP(1007)
+ * Date: 2022-03-19
+ * Description: Cat class
+ */
+
+public class Cat extends Animal {
+	/**
+	 * Constructor. Initialize the name and weight of the cat
+	 */
+	public Cat(String name, double weight) {
+		super(name, weight);
+	}
+
+	/**
+	 * Feeding a cat adds 1.0 to its weight
+	 */
+	public void feed() {
+		setWeight(getWeight() + 1.0);
+	}
+
+	/**
+	 * Test
+	 */
+	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);
+	}
+}

lab/lab5/Question6/Chicken.java

@@ -0,0 +1,28 @@
+/*
+ * Author: CHEN Yongyuan (Walter) 1930006025 from OOP(1007)
+ * Date: 2022-03-19
+ * Description: This is the Chicken class.
+ */
+
+public class Chicken extends Bird {
+	/**
+	 * Constructor of Chicken class. A chicken always has a weight of 5.0 and an
+	 * altitude of 0.0. Chicken spend all their time on the ground.
+	 *
+	 * @param name
+	 */
+	public Chicken(String name) {
+		super(name, 5.0, 0.0);
+	}
+
+	/**
+	 * Test.
+	 */
+	public static void testChicken() {
+		Chicken chk1 = new Chicken("chicken1");
+
+		System.out.println(chk1.getName() == "chicken1");
+		System.out.println(chk1.getWeight() == 5.0);
+		System.out.println(chk1.getAltitude() == 0.0);
+	}
+}

lab/lab5/Question6/Dog.java

@@ -0,0 +1,34 @@
+/*
+ * Author: CHEN Yongyuan (Walter) 1930006025 from OOP(1007)
+ * Date: 2022-03-19
+ * Description: Dog class
+ */
+
+public class Dog extends Animal {
+	/**
+	 * Constructor. Initialize the name and weight of the dog
+	 */
+	public Dog(String name, double weight) {
+		super(name, weight);
+	}
+
+	/**
+	 * Feeding a dog adds 2.0 to its weight
+	 */
+	public void feed() {
+		setWeight(getWeight() + 2.0);
+	}
+
+	/**
+	 * Test
+	 */
+	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);
+	}
+}

lab/lab5/Question6/Start.java

@@ -0,0 +1,44 @@
+/**
+ * Answer to question.
+ *
+ * # Question 4
+ *
+ * Q: 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?
+ *
+ * A: Yes, you can. The Student class has a method getPet() that returns the pet
+ * which is Animal type.
+ *
+ * Q: Can you now use a dog object as the pet of a student? Why or why not?
+ *
+ * A: Yes, you can. But only attributes and methods definded in the Animal class
+ * can be accessed. When you do so, the Dog object will be converted to an
+ * Animal object. Assign a child object to a parent object is called upcasting
+ * in Java. Upcasting is implicit.
+ *
+ * # Question 5
+ *
+ * Q: Where are the name and weight of the bird stored? How?
+ *
+ * A: The Bird class has a private instance variable name and weight which are
+ * inherited from the Animal class.
+ *
+ * Q: Suppose a student has a bird as a pet. Can the student get the altitude of
+ * his pet?
+ *
+ * A: No. The student's pet is an Animal object. The Bird object is a subclass
+ * of Animal. getAltitude is only avaliable in Animal object. When we assign a
+ * Bird to an Animal variable, upcasting happend and only attributes and methods
+ * in the super class can be accessed.
+ *
+ */
+public class Start {
+	public static void main(String[] args) {
+		Cat.testCat();
+		Dog.testDog();
+		Student.testStudent();
+		Animal.testAnimal();
+		Bird.testBird();
+		Chicken.testChicken();
+	}
+}

lab/lab5/Question6/Student.java

@@ -0,0 +1,83 @@
+/*
+ * Author: CHEN Yongyuan (Walter) 1930006025 from OOP(1007)
+ * Date: 2022/03/19
+ * Description: Student class
+ */
+
+public class Student {
+	/**
+	 * Student's name
+	 */
+	private String name;
+
+	/**
+	 * Student's pet
+	 */
+	private Animal pet;
+
+	/**
+	 * Constructor
+	 */
+	public Student(String name, Animal pet) {
+		this.name = name;
+		this.pet = pet;
+	}
+
+	/**
+	 * Getter for name
+	 *
+	 * @return String
+	 */
+	public String getName() {
+		return name;
+	}
+
+	/**
+	 * Getter for pet
+	 *
+	 * @return Animal
+	 */
+	public Animal getPet() {
+		return pet;
+	}
+
+	/**
+	 * Test
+	 */
+	public static void testStudent() {
+		Cat pet = new Cat("Tom", 1.0);
+		Student student = new Student("Walter", pet);
+		System.out.println(student.getName() == "Walter");
+		System.out.println(student.getPet() == pet);
+		System.out.println(student.getPet().getName() == "Tom");
+		System.out.println(student.getPet().getWeight() == 1.0);
+
+		Dog pet2 = new Dog("Jerry", 1.0);
+		Student student2 = new Student("Walter", pet2);
+		System.out.println(student2.getName() == "Walter");
+		System.out.println(student2.getPet() == pet2);
+		System.out.println(student2.getPet().getName() == "Jerry");
+		System.out.println(student2.getPet().getWeight() == 1.0);
+
+		Animal pet3 = new Animal("Unknown animal", 4.0);
+		Student student3 = new Student("Walter", pet3);
+		System.out.println(student3.getName() == "Walter");
+		System.out.println(student3.getPet() == pet3);
+		System.out.println(student3.getPet().getName() == "Unknown animal");
+		System.out.println(student3.getPet().getWeight() == 4.0);
+
+		Bird pet4 = new Bird("bird", 1.0, 39.0);
+		Student student4 = new Student("Walter", pet4);
+		System.out.println(student4.getName() == "Walter");
+		System.out.println(student4.getPet() == pet4);
+		System.out.println(student4.getPet().getName() == "bird");
+		System.out.println(student4.getPet().getWeight() == 1.0);
+
+		Chicken pet5 = new Chicken("chicken");
+		Student student5 = new Student("Walter", pet5);
+		System.out.println(student5.getName() == "Walter");
+		System.out.println(student5.getPet() == pet5);
+		System.out.println(student5.getPet().getName() == "chicken");
+		System.out.println(student5.getPet().getWeight() == 5.0);
+	}
+}

lab/lab5/Question7/Animal.java

@@ -0,0 +1,52 @@
+/*
+ * Author: CHEN Yongyuan (Walter) 1930006025 from OOP(1007)
+ * Date: 2022/03/19
+ * Description: This is the class of Animal.
+ */
+
+public class Animal extends LivingThing {
+	/**
+	 * Animal's weight
+	 */
+	private double weight;
+
+	/**
+	 * Constructor. Initialize the name and weight of the animal.
+	 */
+	public Animal(String name, double weight) {
+		super(name);
+		this.weight = weight;
+	}
+
+	/**
+	 * Get the weight of the animal.
+	 * 
+	 * @return the weight of the animal
+	 */
+	public double getWeight() {
+		return weight;
+	}
+
+	/**
+	 * Set the weight of the animal.
+	 * 
+	 * @param weight
+	 *            the weight of the animal
+	 */
+	public void setWeight(double weight) {
+		this.weight = weight;
+	}
+
+	/**
+	 * Test
+	 */
+	public static void testAnimal() {
+		Animal animal = new Animal("cat", 1.0);
+		System.out.println(animal.getName() == "cat");
+		System.out.println(animal.getWeight() == 1.0);
+		animal.setWeight(2.0);
+		System.out.println(animal.getName() == "cat");
+		System.out.println(animal.getWeight() == 2.0);
+	}
+}
+

lab/lab5/Question7/Bird.java

@@ -0,0 +1,43 @@
+/*
+ * Author: CHEN Yongyuan (Walter) 1930006025 from OOP(1007)
+ * Date: 2022-03-19
+ * Description: This is the class of Bird.
+ */
+
+public class Bird extends Animal {
+	/**
+	 * Altitude of the bird.
+	 */
+	private double altitude;
+
+	/**
+	 * Constructor of Bird.
+	 * 
+	 * @param name     name of the bird
+	 * @param weight   weight of the bird
+	 * @param altitude altitude of the bird
+	 */
+	public Bird(String name, double weight, double altitude) {
+		super(name, weight);
+		this.altitude = altitude;
+	}
+
+	/**
+	 * Get the altitude of the bird.
+	 * 
+	 * @return altitude of the bird
+	 */
+	public double getAltitude() {
+		return altitude;
+	}
+
+	/**
+	 * Test
+	 */
+	public static void testBird() {
+		Bird bird = new Bird("Bird", 1.0, 10.0);
+		System.out.println(bird.getName() == "Bird");
+		System.out.println(bird.getWeight() == 1.0);
+		System.out.println(bird.getAltitude() == 10.0);
+	}
+}

lab/lab5/Question7/Cat.java

@@ -0,0 +1,35 @@
+/*
+ * Author: CHEN Yongyuan (Walter) 1930006025 from OOP(1007)
+ * Date: 2022-03-19
+ * Description: Cat class
+ */
+
+public class Cat extends Animal {
+	/**
+	 * Constructor. Initialize the name and weight of the cat
+	 */
+	public Cat(String name, double weight) {
+		super(name, weight);
+	}
+
+	/**
+	 * Feeding a cat adds 1.0 to its weight
+	 */
+	public void feed() {
+		setWeight(getWeight() + 1.0);
+	}
+
+	/**
+	 * Test
+	 */
+	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);
+	}
+}

lab/lab5/Question7/Chicken.java

@@ -0,0 +1,28 @@
+/*
+ * Author: CHEN Yongyuan (Walter) 1930006025 from OOP(1007)
+ * Date: 2022-03-19
+ * Description: This is the Chicken class.
+ */
+
+public class Chicken extends Bird {
+	/**
+	 * Constructor of Chicken class. A chicken always has a weight of 5.0 and an
+	 * altitude of 0.0. Chicken spend all their time on the ground.
+	 *
+	 * @param name
+	 */
+	public Chicken(String name) {
+		super(name, 5.0, 0.0);
+	}
+
+	/**
+	 * Test.
+	 */
+	public static void testChicken() {
+		Chicken chk1 = new Chicken("chicken1");
+
+		System.out.println(chk1.getName() == "chicken1");
+		System.out.println(chk1.getWeight() == 5.0);
+		System.out.println(chk1.getAltitude() == 0.0);
+	}
+}

lab/lab5/Question7/Dog.java

@@ -0,0 +1,34 @@
+/*
+ * Author: CHEN Yongyuan (Walter) 1930006025 from OOP(1007)
+ * Date: 2022-03-19
+ * Description: Dog class
+ */
+
+public class Dog extends Animal {
+	/**
+	 * Constructor. Initialize the name and weight of the dog
+	 */
+	public Dog(String name, double weight) {
+		super(name, weight);
+	}
+
+	/**
+	 * Feeding a dog adds 2.0 to its weight
+	 */
+	public void feed() {
+		setWeight(getWeight() + 2.0);
+	}
+
+	/**
+	 * Test
+	 */
+	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);
+	}
+}

lab/lab5/Question7/LivingThing.java

@@ -0,0 +1,38 @@
+/*
+ * AutoRobot: CHEN Yongyuan (Walter) 1930006025 from OOP(1007)
+ * Date: 2022-03-19
+ * Description: This is the class of LivingThing.
+ */
+
+public class LivingThing {
+	/**
+	 * Name of the LivingThing.
+	 */
+	private String name;
+
+	/**
+	 * Constructor of LivingThing.
+	 * 
+	 * @param name Name of the LivingThing.
+	 */
+	public LivingThing(String name) {
+		this.name = name;
+	}
+
+	/**
+	 * Get the name of the LivingThing.
+	 * 
+	 * @return The name of the LivingThing.
+	 */
+	public String getName() {
+		return name;
+	}
+
+	/**
+	 * Test.
+	 */
+	public static void testLiving() {
+		LivingThing living = new LivingThing("LivingThing");
+		System.out.println(living.getName() == "LivingThing");
+	}
+}

lab/lab5/Question7/Start.java

@@ -0,0 +1,45 @@
+/**
+ * Answer to question.
+ *
+ * # Question 4
+ *
+ * Q: 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?
+ *
+ * A: Yes, you can. The Student class has a method getPet() that returns the pet
+ * which is Animal type.
+ *
+ * Q: Can you now use a dog object as the pet of a student? Why or why not?
+ *
+ * A: Yes, you can. But only attributes and methods definded in the Animal class
+ * can be accessed. When you do so, the Dog object will be converted to an
+ * Animal object. Assign a child object to a parent object is called upcasting
+ * in Java. Upcasting is implicit.
+ *
+ * # Question 5
+ *
+ * Q: Where are the name and weight of the bird stored? How?
+ *
+ * A: The Bird class has a private instance variable name and weight which are
+ * inherited from the Animal class.
+ *
+ * Q: Suppose a student has a bird as a pet. Can the student get the altitude of
+ * his pet?
+ *
+ * A: No. The student's pet is an Animal object. The Bird object is a subclass
+ * of Animal. getAltitude is only avaliable in Animal object. When we assign a
+ * Bird to an Animal variable, upcasting happend and only attributes and methods
+ * in the super class can be accessed.
+ *
+ */
+public class Start {
+	public static void main(String[] args) {
+		Cat.testCat();
+		Dog.testDog();
+		Student.testStudent();
+		Animal.testAnimal();
+		Bird.testBird();
+		Chicken.testChicken();
+		LivingThing.testLiving();
+	}
+}

lab/lab5/Question7/Student.java

@@ -0,0 +1,69 @@
+/*
+ * Author: CHEN Yongyuan (Walter) 1930006025 from OOP(1007)
+ * Date: 2022/03/19
+ * Description: Student class
+ */
+
+public class Student extends LivingThing {
+	/**
+	 * Student's pet
+	 */
+	private Animal pet;
+
+	/**
+	 * Constructor
+	 */
+	public Student(String name, Animal pet) {
+		super(name);
+		this.pet = pet;
+	}
+
+	/**
+	 * Getter for pet
+	 *
+	 * @return Animal
+	 */
+	public Animal getPet() {
+		return pet;
+	}
+
+	/**
+	 * Test
+	 */
+	public static void testStudent() {
+		Cat pet = new Cat("Tom", 1.0);
+		Student student = new Student("Walter", pet);
+		System.out.println(student.getName() == "Walter");
+		System.out.println(student.getPet() == pet);
+		System.out.println(student.getPet().getName() == "Tom");
+		System.out.println(student.getPet().getWeight() == 1.0);
+
+		Dog pet2 = new Dog("Jerry", 1.0);
+		Student student2 = new Student("Walter", pet2);
+		System.out.println(student2.getName() == "Walter");
+		System.out.println(student2.getPet() == pet2);
+		System.out.println(student2.getPet().getName() == "Jerry");
+		System.out.println(student2.getPet().getWeight() == 1.0);
+
+		Animal pet3 = new Animal("Unknown animal", 4.0);
+		Student student3 = new Student("Walter", pet3);
+		System.out.println(student3.getName() == "Walter");
+		System.out.println(student3.getPet() == pet3);
+		System.out.println(student3.getPet().getName() == "Unknown animal");
+		System.out.println(student3.getPet().getWeight() == 4.0);
+
+		Bird pet4 = new Bird("bird", 1.0, 39.0);
+		Student student4 = new Student("Walter", pet4);
+		System.out.println(student4.getName() == "Walter");
+		System.out.println(student4.getPet() == pet4);
+		System.out.println(student4.getPet().getName() == "bird");
+		System.out.println(student4.getPet().getWeight() == 1.0);
+
+		Chicken pet5 = new Chicken("chicken");
+		Student student5 = new Student("Walter", pet5);
+		System.out.println(student5.getName() == "Walter");
+		System.out.println(student5.getPet() == pet5);
+		System.out.println(student5.getPet().getName() == "chicken");
+		System.out.println(student5.getPet().getWeight() == 5.0);
+	}
+}