lab 9 close #7

lab/lab9/Question1/BadCarException.java

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+/*
+ * BadCarException
+ */
+
+public class BadCarException extends Exception {
+	// generate serial version ID by class name
+	private static final long serialVersionUID = BadCarException.class.getName().hashCode();
+
+	public BadCarException() {
+		super();
+	}
+
+	public BadCarException(String message) {
+		super(message);
+	}
+}

lab/lab9/Question1/BadDoorException.java

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+/*
+ * BadDoorException
+ */
+
+public class BadDoorException extends Exception {
+	// generate serial version ID by class name
+	private static final long serialVersionUID = BadDoorException.class.getName().hashCode();
+
+	public BadDoorException() {
+		super();
+	}
+
+	public BadDoorException(String message) {
+		super(message);
+	}
+}

lab/lab9/Question1/Car.java

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+/*
+ * Author: CHEN Yongyuan (Walter) 1930006025 from OOP(1007)
+ * Date: 2022-04-21
+ * Description: This is the class of Door.
+ */
+
+public class Car {
+	private String name;
+	private Door[] doors;
+
+	/**
+	 * Constructor.
+	 *
+	 * @param name          The name of the car.
+	 * @param numberOfDoors The number of doors.
+	 * @throws BadCarException If the number of doors is less than 1.
+	 */
+	public Car(String name, int numberOfDoors) throws BadCarException {
+		if (numberOfDoors < 1) {
+			throw new BadCarException("A car must have at least one door!");
+		}
+
+		this.name = name;
+
+		// initialise the doors array
+		doors = new Door[numberOfDoors];
+		for (int i = 0; i < numberOfDoors; i++) {
+			doors[i] = new Door();
+		}
+	}
+
+	/**
+	 * Prints each door of the car.
+	 */
+	public void listDoors() {
+		for (Door door : doors) {
+			System.out.println(String.format("%s: door is %s", name, door.isOpen() ? "open" : "closed"));
+		}
+	}
+
+	/**
+	 * Count the numer of open doors.
+	 *
+	 * @return The number of open doors.
+	 */
+	public int countOpenDoors() {
+		int count = 0;
+		for (Door door : doors) {
+			if (door.isOpen()) {
+				count++;
+			}
+		}
+		return count;
+	}
+
+	/**
+	 * Open one door with number start from 1.
+	 *
+	 * @param doorNumber The number of the door to open start from 1.
+	 * @throws BadDoorException If try to open a non-existed door.
+	 */
+	public void openOneDoor(int doorNumber) throws BadDoorException {
+		doorNumber--;
+		if (doorNumber < 0 || doorNumber >= doors.length || doors[doorNumber] == null) {
+			throw new BadDoorException(String.format("Door %d does not exist!", doorNumber+1));
+		}
+
+		doors[doorNumber].open();
+	}
+
+	/**
+	 * Test.
+	 */
+	public static void testCar() {
+		try {
+			Car brokencar = new Car("Broken", 0);
+		} catch (BadCarException ex) {
+			System.out.println(ex.getMessage() == "A car must have at least one door!");
+		}
+		Car c = null;
+		try {
+			c = new Car("Biggy", 7);
+		} catch (BadCarException ex) {
+			System.out.println("BUG! This must never happen!");
+		}
+		c.listDoors();
+		System.out.println(c.countOpenDoors() == 0);
+		try {
+			c.openOneDoor(8);
+		} catch (BadDoorException ex) {
+			System.out.println(ex.getMessage().equals("Door 8 does not exist!"));
+		}
+		try {
+			c.openOneDoor(3);
+		} catch (BadDoorException ex) {
+			System.out.println("BUG! This must never happen!");
+		}
+		System.out.println(c.countOpenDoors() == 1);
+	}
+}

lab/lab9/Question1/Door.java

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+/*
+ * Author: CHEN Yongyuan (Walter) 1930006025 from OOP(1007)
+ * Date: 2022-04-21
+ * Description: This is the class of Door.
+ */
+
+public class Door {
+	/**
+	 * Indicator of whether the door is open or not. Default is closed
+	 */
+	private boolean isOpen;
+
+	/**
+	 * Constructor.
+	 */
+	public Door() {
+		isOpen = false;
+	}
+
+	/**
+	 * Get whether the door is open or not.
+	 *
+	 * @return true if the door is open, false otherwise
+	 */
+	public boolean isOpen() {
+		return isOpen;
+	}
+
+	/**
+	 * Open the door.
+	 */
+	public void open() {
+		isOpen = true;
+	}
+
+	/**
+	 * Close the door.
+	 */
+	public void close() {
+		isOpen = false;
+	}
+
+	/**
+	 * Test.
+	 */
+	public static void testDoor() {
+		Door d = new Door();
+		System.out.println(d.isOpen() == false);
+		d.close();
+		System.out.println(d.isOpen() == false);
+		d.open();
+		System.out.println(d.isOpen() == true);
+	}
+}

lab/lab9/Question1/Start.java

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+public class Start {
+	public static void main(String[] args) {
+		Door.testDoor();
+		Car.testCar();
+	}
+}

lab/lab9/Question2/BadCarException.java

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+/*
+ * BadCarException
+ */
+
+public class BadCarException extends Exception {
+	// generate serial version ID by class name
+	private static final long serialVersionUID = BadCarException.class.getName().hashCode();
+
+	public BadCarException() {
+		super();
+	}
+
+	public BadCarException(String message) {
+		super(message);
+	}
+}

lab/lab9/Question2/BadDoorException.java

@@ -0,0 +1,16 @@
+/*
+ * BadDoorException
+ */
+
+public class BadDoorException extends Exception {
+	// generate serial version ID by class name
+	private static final long serialVersionUID = BadDoorException.class.getName().hashCode();
+
+	public BadDoorException() {
+		super();
+	}
+
+	public BadDoorException(String message) {
+		super(message);
+	}
+}

lab/lab9/Question2/Car.java

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+/*
+ * Author: CHEN Yongyuan (Walter) 1930006025 from OOP(1007)
+ * Date: 2022-04-21
+ * Description: This is the class of Door.
+ */
+
+public class Car {
+	private String name;
+	private Door[] doors;
+
+	/**
+	 * Constructor.
+	 *
+	 * @param name          The name of the car.
+	 * @param numberOfDoors The number of doors.
+	 * @throws BadCarException If the number of doors is less than 1.
+	 */
+	public Car(String name, int numberOfDoors) throws BadCarException {
+		if (numberOfDoors < 1) {
+			throw new BadCarException("A car must have at least one door!");
+		}
+
+		this.name = name;
+
+		// initialise the doors array
+		doors = new Door[numberOfDoors];
+		for (int i = 0; i < numberOfDoors; i++) {
+			doors[i] = new Door();
+		}
+	}
+
+	/**
+	 * Prints each door of the car.
+	 */
+	public void listDoors() {
+		for (Door door : doors) {
+			System.out.println(String.format("%s: door is %s", name, door.isOpen() ? "open" : "closed"));
+		}
+	}
+
+	/**
+	 * Count the numer of open doors.
+	 *
+	 * @return The number of open doors.
+	 */
+	public int countOpenDoors() {
+		int count = 0;
+		for (Door door : doors) {
+			if (door.isOpen()) {
+				count++;
+			}
+		}
+		return count;
+	}
+
+	/**
+	 * Open one door with number start from 1.
+	 *
+	 * @param doorNumber The number of the door to open start from 1.
+	 * @throws BadDoorException If try to open a non-existed door.
+	 */
+	public void openOneDoor(int doorNumber) throws BadDoorException {
+		doorNumber--;
+		if (doorNumber < 0 || doorNumber >= doors.length || doors[doorNumber] == null) {
+			throw new BadDoorException(String.format("Door %d does not exist!", doorNumber + 1));
+		}
+
+		doors[doorNumber].open();
+	}
+
+	/**
+	 * Open all the closed doors and closes all the open doors.
+	 */
+	public void changeAllDoors() {
+		for (Door door : doors) {
+			if (door.isOpen()) {
+				door.close();
+			} else {
+				door.open();
+			}
+		}
+	}
+
+	/**
+	 * Test.
+	 */
+	public static void testCar() {
+		try {
+			Car brokencar = new Car("Broken", 0);
+		} catch (BadCarException ex) {
+			System.out.println(ex.getMessage() == "A car must have at least one door!");
+		}
+		Car c = null;
+		try {
+			c = new Car("Biggy", 7);
+		} catch (BadCarException ex) {
+			System.out.println("BUG! This must never happen!");
+		}
+		c.listDoors();
+		System.out.println(c.countOpenDoors() == 0);
+		c.changeAllDoors();
+		System.out.println(c.countOpenDoors() == 7);
+		c.listDoors();
+		c.changeAllDoors();
+		System.out.println(c.countOpenDoors() == 0);
+		try {
+			c.openOneDoor(8);
+		} catch (BadDoorException ex) {
+			System.out.println(ex.getMessage().equals("Door 8 does not exist!"));
+		}
+		try {
+			c.openOneDoor(3);
+		} catch (BadDoorException ex) {
+			System.out.println("BUG! This must never happen!");
+		}
+		System.out.println(c.countOpenDoors() == 1);
+		c.changeAllDoors();
+		System.out.println(c.countOpenDoors() == 6);
+		c.listDoors();
+		c.changeAllDoors();
+		System.out.println(c.countOpenDoors() == 1);
+		c.listDoors();
+	}
+}

lab/lab9/Question2/Door.java

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+/*
+ * Author: CHEN Yongyuan (Walter) 1930006025 from OOP(1007)
+ * Date: 2022-04-21
+ * Description: This is the class of Door.
+ */
+
+public class Door {
+	/**
+	 * Indicator of whether the door is open or not. Default is closed
+	 */
+	private boolean isOpen;
+
+	/**
+	 * Constructor.
+	 */
+	public Door() {
+		isOpen = false;
+	}
+
+	/**
+	 * Get whether the door is open or not.
+	 *
+	 * @return true if the door is open, false otherwise
+	 */
+	public boolean isOpen() {
+		return isOpen;
+	}
+
+	/**
+	 * Open the door.
+	 */
+	public void open() {
+		isOpen = true;
+	}
+
+	/**
+	 * Close the door.
+	 */
+	public void close() {
+		isOpen = false;
+	}
+
+	/**
+	 * Test.
+	 */
+	public static void testDoor() {
+		Door d = new Door();
+		System.out.println(d.isOpen() == false);
+		d.close();
+		System.out.println(d.isOpen() == false);
+		d.open();
+		System.out.println(d.isOpen() == true);
+	}
+}

lab/lab9/Question2/Start.java

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+public class Start {
+	public static void main(String[] args) {
+		Door.testDoor();
+		Car.testCar();
+	}
+}

lab/lab9/Question3/BadCarException.java

@@ -0,0 +1,16 @@
+/*
+ * BadCarException
+ */
+
+public class BadCarException extends Exception {
+	// generate serial version ID by class name
+	private static final long serialVersionUID = BadCarException.class.getName().hashCode();
+
+	public BadCarException() {
+		super();
+	}
+
+	public BadCarException(String message) {
+		super(message);
+	}
+}

lab/lab9/Question3/BadDoorException.java

@@ -0,0 +1,16 @@
+/*
+ * BadDoorException
+ */
+
+public class BadDoorException extends Exception {
+	// generate serial version ID by class name
+	private static final long serialVersionUID = BadDoorException.class.getName().hashCode();
+
+	public BadDoorException() {
+		super();
+	}
+
+	public BadDoorException(String message) {
+		super(message);
+	}
+}

lab/lab9/Question3/Car.java

@@ -0,0 +1,156 @@
+/*
+ * Author: CHEN Yongyuan (Walter) 1930006025 from OOP(1007)
+ * Date: 2022-04-21
+ * Description: This is the class of Door.
+ */
+
+public class Car {
+	private String name;
+	private Door[] doors;
+
+	/**
+	 * Constructor.
+	 *
+	 * @param name          The name of the car.
+	 * @param numberOfDoors The number of doors.
+	 * @throws BadCarException If the number of doors is less than 1.
+	 */
+	public Car(String name, int numberOfDoors) throws BadCarException {
+		if (numberOfDoors < 1) {
+			throw new BadCarException("A car must have at least one door!");
+		}
+
+		this.name = name;
+
+		// initialise the doors array
+		doors = new Door[numberOfDoors];
+		for (int i = 0; i < numberOfDoors; i++) {
+			doors[i] = new Door();
+		}
+	}
+
+	/**
+	 * Prints each door of the car.
+	 */
+	public void listDoors() {
+		for (Door door : doors) {
+			System.out.println(String.format("%s: door is %s", name, door.isOpen() ? "open" : "closed"));
+		}
+	}
+
+	/**
+	 * Count the numer of open doors.
+	 *
+	 * @return The number of open doors.
+	 */
+	public int countOpenDoors() {
+		int count = 0;
+		for (Door door : doors) {
+			if (door.isOpen()) {
+				count++;
+			}
+		}
+		return count;
+	}
+
+	/**
+	 * Open one door with number start from 1.
+	 *
+	 * @param doorNumber The number of the door to open start from 1.
+	 * @throws BadDoorException If try to open a non-existed door.
+	 */
+	public void openOneDoor(int doorNumber) throws BadDoorException {
+		doorNumber--;
+		if (doorNumber < 0 || doorNumber >= doors.length || doors[doorNumber] == null) {
+			throw new BadDoorException(String.format("Door %d does not exist!", doorNumber + 1));
+		}
+
+		doors[doorNumber].open();
+	}
+
+	/**
+	 * Open all the closed doors and closes all the open doors.
+	 */
+	public void changeAllDoors() {
+		for (Door door : doors) {
+			if (door.isOpen()) {
+				door.close();
+			} else {
+				door.open();
+			}
+		}
+	}
+
+	/**
+	 * Replaces the existing car door with a completely new door.
+	 *
+	 * @param doorNumber The number of the door to replace start from 1.
+	 * @throws BadDoorException if replace a non-existed door.
+	 */
+	public void replaceDoor(int doorNumber) throws BadDoorException {
+		doorNumber--;
+		if (doorNumber < 0 || doorNumber >= doors.length || doors[doorNumber] == null) {
+			throw new BadDoorException(String.format("Door %d does not exist!", doorNumber + 1));
+		}
+
+		// replace the door.
+		doors[doorNumber] = new Door();
+	}
+
+	/**
+	 * Test.
+	 */
+	public static void testCar() {
+		try {
+			Car brokencar = new Car("Broken", 0);
+		} catch (BadCarException ex) {
+			System.out.println(ex.getMessage() == "A car must have at least one door!");
+		}
+		Car c = null;
+		try {
+			c = new Car("Biggy", 7);
+		} catch (BadCarException ex) {
+			System.out.println("BUG! This must never happen!");
+		}
+		c.listDoors();
+		System.out.println(c.countOpenDoors() == 0);
+		c.changeAllDoors();
+		System.out.println(c.countOpenDoors() == 7);
+		c.listDoors();
+		c.changeAllDoors();
+		System.out.println(c.countOpenDoors() == 0);
+		try {
+			c.openOneDoor(8);
+		} catch (BadDoorException ex) {
+			System.out.println(ex.getMessage().equals("Door 8 does not exist!"));
+		}
+		try {
+			c.openOneDoor(3);
+		} catch (BadDoorException ex) {
+			System.out.println("BUG! This must never happen!");
+		}
+		System.out.println(c.countOpenDoors() == 1);
+
+		c.changeAllDoors();
+		System.out.println(c.countOpenDoors() == 6);
+		c.listDoors();
+		c.changeAllDoors();
+		System.out.println(c.countOpenDoors() == 1);
+		c.listDoors();
+		try {
+			c.replaceDoor(8);
+		} catch (BadDoorException ex) {
+
+			System.out.println(ex.getMessage().equals("Door 8 does not exist!"));
+		}
+
+		try {
+			c.replaceDoor(3);
+		} catch (BadDoorException ex) {
+			System.out.println("BUG! This must never happen!");
+		}
+		System.out.println(c.countOpenDoors() == 0);
+
+		c.listDoors();
+	}
+}

lab/lab9/Question3/Door.java

@@ -0,0 +1,54 @@
+/*
+ * Author: CHEN Yongyuan (Walter) 1930006025 from OOP(1007)
+ * Date: 2022-04-21
+ * Description: This is the class of Door.
+ */
+
+public class Door {
+	/**
+	 * Indicator of whether the door is open or not. Default is closed
+	 */
+	private boolean isOpen;
+
+	/**
+	 * Constructor.
+	 */
+	public Door() {
+		isOpen = false;
+	}
+
+	/**
+	 * Get whether the door is open or not.
+	 *
+	 * @return true if the door is open, false otherwise
+	 */
+	public boolean isOpen() {
+		return isOpen;
+	}
+
+	/**
+	 * Open the door.
+	 */
+	public void open() {
+		isOpen = true;
+	}
+
+	/**
+	 * Close the door.
+	 */
+	public void close() {
+		isOpen = false;
+	}
+
+	/**
+	 * Test.
+	 */
+	public static void testDoor() {
+		Door d = new Door();
+		System.out.println(d.isOpen() == false);
+		d.close();
+		System.out.println(d.isOpen() == false);
+		d.open();
+		System.out.println(d.isOpen() == true);
+	}
+}

lab/lab9/Question3/Start.java

@@ -0,0 +1,6 @@
+public class Start {
+	public static void main(String[] args) {
+		Door.testDoor();
+		Car.testCar();
+	}
+}

lab/lab9/Question4/BadCarException.java

@@ -0,0 +1,16 @@
+/*
+ * BadCarException
+ */
+
+public class BadCarException extends Exception {
+	// generate serial version ID by class name
+	private static final long serialVersionUID = BadCarException.class.getName().hashCode();
+
+	public BadCarException() {
+		super();
+	}
+
+	public BadCarException(String message) {
+		super(message);
+	}
+}

lab/lab9/Question4/BadDoorException.java

@@ -0,0 +1,16 @@
+/*
+ * BadDoorException
+ */
+
+public class BadDoorException extends Exception {
+	// generate serial version ID by class name
+	private static final long serialVersionUID = BadDoorException.class.getName().hashCode();
+
+	public BadDoorException() {
+		super();
+	}
+
+	public BadDoorException(String message) {
+		super(message);
+	}
+}

lab/lab9/Question4/Car.java

@@ -0,0 +1,170 @@
+/*
+ * Author: CHEN Yongyuan (Walter) 1930006025 from OOP(1007)
+ * Date: 2022-04-21
+ * Description: This is the class of Door.
+ */
+
+public class Car {
+	private String name;
+	private Door[] doors;
+
+	/**
+	 * Constructor.
+	 *
+	 * @param name          The name of the car.
+	 * @param numberOfDoors The number of doors.
+	 * @throws BadCarException If the number of doors is less than 1.
+	 */
+	public Car(String name, int numberOfDoors) throws BadCarException {
+		if (numberOfDoors < 1) {
+			throw new BadCarException("A car must have at least one door!");
+		}
+
+		this.name = name;
+
+		// initialise the doors array
+		doors = new Door[numberOfDoors];
+		for (int i = 0; i < numberOfDoors; i++) {
+			doors[i] = new Door();
+		}
+	}
+
+	/**
+	 * Prints each door of the car.
+	 */
+	public void listDoors() {
+		for (Door door : doors) {
+			System.out.println(String.format("%s: door is %s", name, door.isOpen() ? "open" : "closed"));
+		}
+	}
+
+	/**
+	 * Count the numer of open doors.
+	 *
+	 * @return The number of open doors.
+	 */
+	public int countOpenDoors() {
+		int count = 0;
+		for (Door door : doors) {
+			if (door.isOpen()) {
+				count++;
+			}
+		}
+		return count;
+	}
+
+	/**
+	 * Open one door with number start from 1.
+	 *
+	 * @param doorNumber The number of the door to open start from 1.
+	 * @throws BadDoorException If try to open a non-existed door.
+	 */
+	public void openOneDoor(int doorNumber) throws BadDoorException {
+		doorNumber--;
+		if (doorNumber < 0 || doorNumber >= doors.length || doors[doorNumber] == null) {
+			throw new BadDoorException(String.format("Door %d does not exist!", doorNumber + 1));
+		}
+
+		doors[doorNumber].open();
+	}
+
+	/**
+	 * Open all the closed doors and closes all the open doors.
+	 */
+	public void changeAllDoors() {
+		for (Door door : doors) {
+			if (door.isOpen()) {
+				door.close();
+			} else {
+				door.open();
+			}
+		}
+	}
+
+	/**
+	 * Replaces the existing car door with a completely new door.
+	 *
+	 * @param doorNumber The number of the door to replace start from 1.
+	 * @throws BadDoorException if replace a non-existed door.
+	 */
+	public void replaceDoor(int doorNumber) throws BadDoorException {
+		doorNumber--;
+		if (doorNumber < 0 || doorNumber >= doors.length || doors[doorNumber] == null) {
+			throw new BadDoorException(String.format("Door %d does not exist!", doorNumber + 1));
+		}
+
+		// replace the door.
+		doors[doorNumber] = new Door();
+	}
+
+	/**
+	 * Replace all doors.
+	 */
+	public void replaceAllDoors() {
+		for (int i = 0; i < doors.length; i++) {
+			doors[i] = new Door();
+		}
+	}
+
+	/**
+	 * Test.
+	 */
+	public static void testCar() {
+		try {
+			Car brokencar = new Car("Broken", 0);
+		} catch (BadCarException ex) {
+			System.out.println(ex.getMessage() == "A car must have at least one door!");
+		}
+		Car c = null;
+		try {
+			c = new Car("Biggy", 7);
+		} catch (BadCarException ex) {
+			System.out.println("BUG! This must never happen!");
+		}
+		c.listDoors();
+		System.out.println(c.countOpenDoors() == 0);
+		c.changeAllDoors();
+		System.out.println(c.countOpenDoors() == 7);
+		c.listDoors();
+		c.changeAllDoors();
+		System.out.println(c.countOpenDoors() == 0);
+		try {
+			c.openOneDoor(8);
+		} catch (BadDoorException ex) {
+			System.out.println(ex.getMessage().equals("Door 8 does not exist!"));
+		}
+		try {
+			c.openOneDoor(3);
+		} catch (BadDoorException ex) {
+			System.out.println("BUG! This must never happen!");
+		}
+		System.out.println(c.countOpenDoors() == 1);
+
+		c.changeAllDoors();
+		System.out.println(c.countOpenDoors() == 6);
+		c.listDoors();
+		c.changeAllDoors();
+		System.out.println(c.countOpenDoors() == 1);
+		c.listDoors();
+		try {
+			c.replaceDoor(8);
+		} catch (BadDoorException ex) {
+
+			System.out.println(ex.getMessage().equals("Door 8 does not exist!"));
+		}
+
+		try {
+			c.replaceDoor(3);
+		} catch (BadDoorException ex) {
+			System.out.println("BUG! This must never happen!");
+		}
+		System.out.println(c.countOpenDoors() == 0);
+		c.listDoors();
+		c.changeAllDoors();
+		System.out.println(c.countOpenDoors() == 7);
+		c.listDoors();
+		c.replaceAllDoors();
+		System.out.println(c.countOpenDoors() == 0);
+		c.listDoors();
+	}
+}

lab/lab9/Question4/Door.java

@@ -0,0 +1,54 @@
+/*
+ * Author: CHEN Yongyuan (Walter) 1930006025 from OOP(1007)
+ * Date: 2022-04-21
+ * Description: This is the class of Door.
+ */
+
+public class Door {
+	/**
+	 * Indicator of whether the door is open or not. Default is closed
+	 */
+	private boolean isOpen;
+
+	/**
+	 * Constructor.
+	 */
+	public Door() {
+		isOpen = false;
+	}
+
+	/**
+	 * Get whether the door is open or not.
+	 *
+	 * @return true if the door is open, false otherwise
+	 */
+	public boolean isOpen() {
+		return isOpen;
+	}
+
+	/**
+	 * Open the door.
+	 */
+	public void open() {
+		isOpen = true;
+	}
+
+	/**
+	 * Close the door.
+	 */
+	public void close() {
+		isOpen = false;
+	}
+
+	/**
+	 * Test.
+	 */
+	public static void testDoor() {
+		Door d = new Door();
+		System.out.println(d.isOpen() == false);
+		d.close();
+		System.out.println(d.isOpen() == false);
+		d.open();
+		System.out.println(d.isOpen() == true);
+	}
+}

lab/lab9/Question4/Start.java

@@ -0,0 +1,17 @@
+/**
+ * Answer to questions.
+ *
+ * - Q4: What happends if you try to use am enhanced for loop?
+ *
+ * - A: The original doors will not be replace. When you use for (Door door :
+ * doors), JVM will copy the value to door (or copy the address). If you set
+ * door = new Door(), the new door will be assigned to that copied object,
+ * istead of the object in array.
+ *
+ */
+public class Start {
+	public static void main(String[] args) {
+		Door.testDoor();
+		Car.testCar();
+	}
+}

lab/lab9/Question5/BadCarException.java

@@ -0,0 +1,16 @@
+/*
+ * BadCarException
+ */
+
+public class BadCarException extends Exception {
+	// generate serial version ID by class name
+	private static final long serialVersionUID = BadCarException.class.getName().hashCode();
+
+	public BadCarException() {
+		super();
+	}
+
+	public BadCarException(String message) {
+		super(message);
+	}
+}

lab/lab9/Question5/BadDoorException.java

@@ -0,0 +1,16 @@
+/*
+ * BadDoorException
+ */
+
+public class BadDoorException extends Exception {
+	// generate serial version ID by class name
+	private static final long serialVersionUID = BadDoorException.class.getName().hashCode();
+
+	public BadDoorException() {
+		super();
+	}
+
+	public BadDoorException(String message) {
+		super(message);
+	}
+}

lab/lab9/Question5/Car.java

@@ -0,0 +1,196 @@
+/*
+ * Author: CHEN Yongyuan (Walter) 1930006025 from OOP(1007)
+ * Date: 2022-04-21
+ * Description: This is the class of Door.
+ */
+
+public class Car {
+	private String name;
+	private Door[] doors;
+
+	/**
+	 * Constructor.
+	 *
+	 * @param name          The name of the car.
+	 * @param numberOfDoors The number of doors.
+	 * @throws BadCarException If the number of doors is less than 1.
+	 */
+	public Car(String name, int numberOfDoors) throws BadCarException {
+		if (numberOfDoors < 1) {
+			throw new BadCarException("A car must have at least one door!");
+		}
+
+		this.name = name;
+
+		// initialise the doors array
+		doors = new Door[numberOfDoors];
+		for (int i = 0; i < numberOfDoors; i++) {
+			doors[i] = new Door();
+		}
+	}
+
+	/**
+	 * Prints each door of the car.
+	 */
+	public void listDoors() {
+		for (Door door : doors) {
+			System.out.println(String.format("%s: door is %s", name, door.isOpen() ? "open" : "closed"));
+		}
+	}
+
+	/**
+	 * Count the numer of open doors.
+	 *
+	 * @return The number of open doors.
+	 */
+	public int countOpenDoors() {
+		int count = 0;
+		for (Door door : doors) {
+			if (door.isOpen()) {
+				count++;
+			}
+		}
+		return count;
+	}
+
+	/**
+	 * Open one door with number start from 1.
+	 *
+	 * @param doorNumber The number of the door to open start from 1.
+	 * @throws BadDoorException If try to open a non-existed door.
+	 */
+	public void openOneDoor(int doorNumber) throws BadDoorException {
+		doorNumber--;
+		if (doorNumber < 0 || doorNumber >= doors.length || doors[doorNumber] == null) {
+			throw new BadDoorException(String.format("Door %d does not exist!", doorNumber + 1));
+		}
+
+		doors[doorNumber].open();
+	}
+
+	/**
+	 * Open all the closed doors and closes all the open doors.
+	 */
+	public void changeAllDoors() {
+		for (Door door : doors) {
+			if (door.isOpen()) {
+				door.close();
+			} else {
+				door.open();
+			}
+		}
+	}
+
+	/**
+	 * Replaces the existing car door with a completely new door.
+	 *
+	 * @param doorNumber The number of the door to replace start from 1.
+	 * @throws BadDoorException if replace a non-existed door.
+	 */
+	public void replaceDoor(int doorNumber) throws BadDoorException {
+		doorNumber--;
+		if (doorNumber < 0 || doorNumber >= doors.length || doors[doorNumber] == null) {
+			throw new BadDoorException(String.format("Door %d does not exist!", doorNumber + 1));
+		}
+
+		// replace the door.
+		doors[doorNumber] = new Door();
+	}
+
+	/**
+	 * Replace all doors.
+	 */
+	public void replaceAllDoors() {
+		for (int i = 0; i < doors.length; i++) {
+			doors[i] = new Door();
+		}
+	}
+
+	/**
+	 * Replace existing doors start from the first door with the number of doors.
+	 *
+	 * @param numOfDoorsToReplace The number of doors to replace.
+	 */
+	public void replaceManyDoors(int numOfDoorsToReplace) {
+		for (int i = 0; i < numOfDoorsToReplace; i++) {
+			doors[i] = new Door();
+		}
+	}
+
+	/**
+	 * Test.
+	 */
+	public static void testCar() {
+		try {
+			Car brokencar = new Car("Broken", 0);
+		} catch (BadCarException ex) {
+			System.out.println(ex.getMessage() == "A car must have at least one door!");
+		}
+		Car c = null;
+		try {
+			c = new Car("Biggy", 7);
+		} catch (BadCarException ex) {
+			System.out.println("BUG! This must never happen!");
+		}
+		c.listDoors();
+		System.out.println(c.countOpenDoors() == 0);
+		c.changeAllDoors();
+		System.out.println(c.countOpenDoors() == 7);
+		c.listDoors();
+		c.changeAllDoors();
+		System.out.println(c.countOpenDoors() == 0);
+		try {
+			c.openOneDoor(8);
+		} catch (BadDoorException ex) {
+			System.out.println(ex.getMessage().equals("Door 8 does not exist!"));
+		}
+		try {
+			c.openOneDoor(3);
+		} catch (BadDoorException ex) {
+			System.out.println("BUG! This must never happen!");
+		}
+		System.out.println(c.countOpenDoors() == 1);
+
+		c.changeAllDoors();
+		System.out.println(c.countOpenDoors() == 6);
+		c.listDoors();
+		c.changeAllDoors();
+		System.out.println(c.countOpenDoors() == 1);
+		c.listDoors();
+		try {
+			c.replaceDoor(8);
+		} catch (BadDoorException ex) {
+
+			System.out.println(ex.getMessage().equals("Door 8 does not exist!"));
+		}
+
+		try {
+			c.replaceDoor(3);
+		} catch (BadDoorException ex) {
+			System.out.println("BUG! This must never happen!");
+		}
+		System.out.println(c.countOpenDoors() == 0);
+
+		c.listDoors();
+		c.changeAllDoors();
+		System.out.println(c.countOpenDoors() == 7);
+		c.listDoors();
+		c.replaceAllDoors();
+		System.out.println(c.countOpenDoors() == 0);
+		c.listDoors();
+		c.changeAllDoors();
+		System.out.println(c.countOpenDoors() == 7);
+		c.listDoors();
+		c.replaceManyDoors(4);
+		System.out.println(c.countOpenDoors() == 3);
+		c.listDoors();
+		try {
+			c.replaceManyDoors(20);
+		} catch (ArrayIndexOutOfBoundsException ex) {
+			System.out.println(ex.getMessage().equals("Index 7 out of bounds for length 7"));
+		}
+
+		System.out.println(c.countOpenDoors() == 0);
+		c.listDoors();
+	}
+}

lab/lab9/Question5/Door.java

@@ -0,0 +1,54 @@
+/*
+ * Author: CHEN Yongyuan (Walter) 1930006025 from OOP(1007)
+ * Date: 2022-04-21
+ * Description: This is the class of Door.
+ */
+
+public class Door {
+	/**
+	 * Indicator of whether the door is open or not. Default is closed
+	 */
+	private boolean isOpen;
+
+	/**
+	 * Constructor.
+	 */
+	public Door() {
+		isOpen = false;
+	}
+
+	/**
+	 * Get whether the door is open or not.
+	 *
+	 * @return true if the door is open, false otherwise
+	 */
+	public boolean isOpen() {
+		return isOpen;
+	}
+
+	/**
+	 * Open the door.
+	 */
+	public void open() {
+		isOpen = true;
+	}
+
+	/**
+	 * Close the door.
+	 */
+	public void close() {
+		isOpen = false;
+	}
+
+	/**
+	 * Test.
+	 */
+	public static void testDoor() {
+		Door d = new Door();
+		System.out.println(d.isOpen() == false);
+		d.close();
+		System.out.println(d.isOpen() == false);
+		d.open();
+		System.out.println(d.isOpen() == true);
+	}
+}

lab/lab9/Question5/Start.java

@@ -0,0 +1,21 @@
+/**
+ * Answer to questions.
+ *
+ * - Q4: What happends if you try to use am enhanced for loop?
+ *
+ * - A: The original doors will not be replace. When you use for (Door door :
+ * doors), JVM will copy the value to door (or copy the address). If you set
+ * door = new Door(), the new door will be assigned to that copied object,
+ * istead of the object in array.
+ *
+ * - Q5: What happends if you try to replace more doors than the car has?
+ *
+ * - A: It will throw ArrayIndexOutOfBoundsException.
+ *
+ */
+public class Start {
+	public static void main(String[] args) {
+		Door.testDoor();
+		Car.testCar();
+	}
+}

lab/lab9/Question6/BadCarException.java

@@ -0,0 +1,16 @@
+/*
+ * BadCarException
+ */
+
+public class BadCarException extends Exception {
+	// generate serial version ID by class name
+	private static final long serialVersionUID = BadCarException.class.getName().hashCode();
+
+	public BadCarException() {
+		super();
+	}
+
+	public BadCarException(String message) {
+		super(message);
+	}
+}

lab/lab9/Question6/BadDoorException.java

@@ -0,0 +1,16 @@
+/*
+ * BadDoorException
+ */
+
+public class BadDoorException extends Exception {
+	// generate serial version ID by class name
+	private static final long serialVersionUID = BadDoorException.class.getName().hashCode();
+
+	public BadDoorException() {
+		super();
+	}
+
+	public BadDoorException(String message) {
+		super(message);
+	}
+}

lab/lab9/Question6/Car.java

@@ -0,0 +1,220 @@
+/*
+ * Author: CHEN Yongyuan (Walter) 1930006025 from OOP(1007)
+ * Date: 2022-04-21
+ * Description: This is the class of Door.
+ */
+
+public class Car {
+	private String name;
+	private Door[] doors;
+
+	/**
+	 * Constructor.
+	 *
+	 * @param name          The name of the car.
+	 * @param numberOfDoors The number of doors.
+	 * @throws BadCarException If the number of doors is less than 1.
+	 */
+	public Car(String name, int numberOfDoors) throws BadCarException {
+		if (numberOfDoors < 1) {
+			throw new BadCarException("A car must have at least one door!");
+		}
+
+		this.name = name;
+
+		// initialise the doors array
+		doors = new Door[numberOfDoors];
+		for (int i = 0; i < numberOfDoors; i++) {
+			doors[i] = new Door();
+		}
+	}
+
+	/**
+	 * Prints each door of the car.
+	 */
+	public void listDoors() {
+		for (Door door : doors) {
+			System.out.println(String.format("%s: door is %s", name, door.isOpen() ? "open" : "closed"));
+		}
+	}
+
+	/**
+	 * Count the numer of open doors.
+	 *
+	 * @return The number of open doors.
+	 */
+	public int countOpenDoors() {
+		int count = 0;
+		for (Door door : doors) {
+			if (door.isOpen()) {
+				count++;
+			}
+		}
+		return count;
+	}
+
+	/**
+	 * Open one door with number start from 1.
+	 *
+	 * @param doorNumber The number of the door to open start from 1.
+	 * @throws BadDoorException If try to open a non-existed door.
+	 */
+	public void openOneDoor(int doorNumber) throws BadDoorException {
+		doorNumber--;
+		if (doorNumber < 0 || doorNumber >= doors.length || doors[doorNumber] == null) {
+			throw new BadDoorException(String.format("Door %d does not exist!", doorNumber + 1));
+		}
+
+		doors[doorNumber].open();
+	}
+
+	/**
+	 * Open all the closed doors and closes all the open doors.
+	 */
+	public void changeAllDoors() {
+		for (Door door : doors) {
+			if (door.isOpen()) {
+				door.close();
+			} else {
+				door.open();
+			}
+		}
+	}
+
+	/**
+	 * Replaces the existing car door with a completely new door.
+	 *
+	 * @param doorNumber The number of the door to replace start from 1.
+	 * @throws BadDoorException if replace a non-existed door.
+	 */
+	public void replaceDoor(int doorNumber) throws BadDoorException {
+		doorNumber--;
+		if (doorNumber < 0 || doorNumber >= doors.length || doors[doorNumber] == null) {
+			throw new BadDoorException(String.format("Door %d does not exist!", doorNumber + 1));
+		}
+
+		// replace the door.
+		doors[doorNumber] = new Door();
+	}
+
+	/**
+	 * Replace all doors.
+	 */
+	public void replaceAllDoors() {
+		for (int i = 0; i < doors.length; i++) {
+			doors[i] = new Door();
+		}
+	}
+
+	/**
+	 * Replace existing doors start from the first door with the number of doors.
+	 *
+	 * @param numOfDoorsToReplace The number of doors to replace.
+	 */
+	public void replaceManyDoors(int numOfDoorsToReplace) {
+		for (int i = 0; i < numOfDoorsToReplace; i++) {
+			doors[i] = new Door();
+		}
+	}
+
+	/**
+	 * Adds two new doors to the car.
+	 */
+	public void expandCar() {
+		Door[] newDoors = new Door[doors.length + 2];
+
+		// copy the old doors to the new array.
+		for (int i = 0; i < doors.length; i++) {
+			newDoors[i] = doors[i];
+		}
+
+		// initialise the new doors.
+		for (int i = doors.length; i < newDoors.length; i++) {
+			newDoors[i] = new Door();
+		}
+
+		doors = newDoors;
+	}
+
+	/**
+	 * Test.
+	 */
+	public static void testCar() {
+		try {
+			Car brokencar = new Car("Broken", 0);
+		} catch (BadCarException ex) {
+			System.out.println(ex.getMessage() == "A car must have at least one door!");
+		}
+		Car c = null;
+		try {
+			c = new Car("Biggy", 7);
+		} catch (BadCarException ex) {
+			System.out.println("BUG! This must never happen!");
+		}
+		c.listDoors();
+		System.out.println(c.countOpenDoors() == 0);
+		c.changeAllDoors();
+		System.out.println(c.countOpenDoors() == 7);
+		c.listDoors();
+		c.changeAllDoors();
+		System.out.println(c.countOpenDoors() == 0);
+		try {
+			c.openOneDoor(8);
+		} catch (BadDoorException ex) {
+			System.out.println(ex.getMessage().equals("Door 8 does not exist!"));
+		}
+		try {
+			c.openOneDoor(3);
+		} catch (BadDoorException ex) {
+			System.out.println("BUG! This must never happen!");
+		}
+		System.out.println(c.countOpenDoors() == 1);
+
+		c.changeAllDoors();
+		System.out.println(c.countOpenDoors() == 6);
+		c.listDoors();
+		c.changeAllDoors();
+		System.out.println(c.countOpenDoors() == 1);
+		c.listDoors();
+		try {
+			c.replaceDoor(8);
+		} catch (BadDoorException ex) {
+
+			System.out.println(ex.getMessage().equals("Door 8 does not exist!"));
+		}
+
+		try {
+			c.replaceDoor(3);
+		} catch (BadDoorException ex) {
+			System.out.println("BUG! This must never happen!");
+		}
+		System.out.println(c.countOpenDoors() == 0);
+
+		c.listDoors();
+		c.changeAllDoors();
+		System.out.println(c.countOpenDoors() == 7);
+		c.listDoors();
+		c.replaceAllDoors();
+		System.out.println(c.countOpenDoors() == 0);
+		c.listDoors();
+		c.changeAllDoors();
+		System.out.println(c.countOpenDoors() == 7);
+		c.listDoors();
+		c.replaceManyDoors(4);
+		System.out.println(c.countOpenDoors() == 3);
+		c.listDoors();
+		try {
+			c.replaceManyDoors(20);
+		} catch (ArrayIndexOutOfBoundsException ex) {
+			System.out.println(ex.getMessage().equals("Index 7 out of bounds for length 7"));
+		}
+
+		System.out.println(c.countOpenDoors() == 0);
+		c.listDoors();
+
+		c.expandCar();
+		c.changeAllDoors();
+		System.out.println(c.countOpenDoors() == 9);
+		c.listDoors();
+	}
+}

lab/lab9/Question6/Door.java

@@ -0,0 +1,54 @@
+/*
+ * Author: CHEN Yongyuan (Walter) 1930006025 from OOP(1007)
+ * Date: 2022-04-21
+ * Description: This is the class of Door.
+ */
+
+public class Door {
+	/**
+	 * Indicator of whether the door is open or not. Default is closed
+	 */
+	private boolean isOpen;
+
+	/**
+	 * Constructor.
+	 */
+	public Door() {
+		isOpen = false;
+	}
+
+	/**
+	 * Get whether the door is open or not.
+	 *
+	 * @return true if the door is open, false otherwise
+	 */
+	public boolean isOpen() {
+		return isOpen;
+	}
+
+	/**
+	 * Open the door.
+	 */
+	public void open() {
+		isOpen = true;
+	}
+
+	/**
+	 * Close the door.
+	 */
+	public void close() {
+		isOpen = false;
+	}
+
+	/**
+	 * Test.
+	 */
+	public static void testDoor() {
+		Door d = new Door();
+		System.out.println(d.isOpen() == false);
+		d.close();
+		System.out.println(d.isOpen() == false);
+		d.open();
+		System.out.println(d.isOpen() == true);
+	}
+}

lab/lab9/Question6/Start.java

@@ -0,0 +1,21 @@
+/**
+ * Answer to questions.
+ *
+ * - Q4: What happends if you try to use am enhanced for loop?
+ *
+ * - A: The original doors will not be replace. When you use for (Door door :
+ * doors), JVM will copy the value to door (or copy the address). If you set
+ * door = new Door(), the new door will be assigned to that copied object,
+ * istead of the object in array.
+ *
+ * - Q5: What happends if you try to replace more doors than the car has?
+ *
+ * - A: It will throw ArrayIndexOutOfBoundsException.
+ *
+ */
+public class Start {
+	public static void main(String[] args) {
+		Door.testDoor();
+		Car.testCar();
+	}
+}

lab/lab9/Question7/BadCarException.java

@@ -0,0 +1,16 @@
+/*
+ * BadCarException
+ */
+
+public class BadCarException extends Exception {
+	// generate serial version ID by class name
+	private static final long serialVersionUID = BadCarException.class.getName().hashCode();
+
+	public BadCarException() {
+		super();
+	}
+
+	public BadCarException(String message) {
+		super(message);
+	}
+}

lab/lab9/Question7/BadDoorException.java

@@ -0,0 +1,16 @@
+/*
+ * BadDoorException
+ */
+
+public class BadDoorException extends Exception {
+	// generate serial version ID by class name
+	private static final long serialVersionUID = BadDoorException.class.getName().hashCode();
+
+	public BadDoorException() {
+		super();
+	}
+
+	public BadDoorException(String message) {
+		super(message);
+	}
+}

lab/lab9/Question7/Car.java

@@ -0,0 +1,212 @@
+/*
+ * Author: CHEN Yongyuan (Walter) 1930006025 from OOP(1007)
+ * Date: 2022-04-21
+ * Description: This is the class of Door.
+ */
+
+import java.util.ArrayList;
+
+public class Car {
+	private String name;
+	private ArrayList doors;
+
+	/**
+	 * Constructor.
+	 *
+	 * @param name          The name of the car.
+	 * @param numberOfDoors The number of doors.
+	 * @throws BadCarException If the number of doors is less than 1.
+	 */
+	public Car(String name, int numberOfDoors) throws BadCarException {
+		if (numberOfDoors < 1) {
+			throw new BadCarException("A car must have at least one door!");
+		}
+
+		this.name = name;
+
+		// initialise the doors array
+		doors = new ArrayList();
+		for (int i = 0; i < numberOfDoors; i++) {
+			doors.add(new Door());
+		}
+	}
+
+	/**
+	 * Prints each door of the car.
+	 */
+	public void listDoors() {
+		for (int i = 0; i < doors.size(); i++) {
+			Door door = (Door) doors.get(i);
+			System.out.println(String.format("%s: door is %s", name, door.isOpen() ? "open" : "closed"));
+		}
+	}
+
+	/**
+	 * Count the numer of open doors.
+	 *
+	 * @return The number of open doors.
+	 */
+	public int countOpenDoors() {
+		int count = 0;
+		for (int i = 0; i < doors.size(); i++) {
+			Door door = (Door) doors.get(i);
+			if (door.isOpen()) {
+				count++;
+			}
+		}
+		return count;
+	}
+
+	/**
+	 * Open one door with number start from 1.
+	 *
+	 * @param doorNumber The number of the door to open start from 1.
+	 * @throws BadDoorException If try to open a non-existed door.
+	 */
+	public void openOneDoor(int doorNumber) throws BadDoorException {
+		doorNumber--;
+		if (doorNumber < 0 || doorNumber >= doors.size() || doors.get(doorNumber) == null) {
+			throw new BadDoorException(String.format("Door %d does not exist!", doorNumber + 1));
+		}
+
+		Door door = (Door) doors.get(doorNumber);
+		door.open();
+	}
+
+	/**
+	 * Open all the closed doors and closes all the open doors.
+	 */
+	public void changeAllDoors() {
+		for (int i = 0; i < doors.size(); i++) {
+			Door door = (Door) doors.get(i);
+			if (door.isOpen()) {
+				door.close();
+			} else {
+				door.open();
+			}
+		}
+	}
+
+	/**
+	 * Replaces the existing car door with a completely new door.
+	 *
+	 * @param doorNumber The number of the door to replace start from 1.
+	 * @throws BadDoorException if replace a non-existed door.
+	 */
+	public void replaceDoor(int doorNumber) throws BadDoorException {
+		doorNumber--;
+		if (doorNumber < 0 || doorNumber >= doors.size() || doors.get(doorNumber) == null) {
+			throw new BadDoorException(String.format("Door %d does not exist!", doorNumber + 1));
+		}
+
+		// replace the door.
+		doors.set(doorNumber, new Door());
+	}
+
+	/**
+	 * Replace all doors.
+	 */
+	public void replaceAllDoors() {
+		for (int i = 0; i < doors.size(); i++) {
+			doors.set(i, new Door());
+		}
+	}
+
+	/**
+	 * Replace existing doors start from the first door with the number of doors.
+	 *
+	 * @param numOfDoorsToReplace The number of doors to replace.
+	 */
+	public void replaceManyDoors(int numOfDoorsToReplace) {
+		for (int i = 0; i < numOfDoorsToReplace; i++) {
+			doors.set(i, new Door());
+		}
+	}
+
+	/**
+	 * Adds two new doors to the car.
+	 */
+	public void expandCar() {
+		doors.add(new Door());
+		doors.add(new Door());
+	}
+
+	/**
+	 * Test.
+	 */
+	public static void testCar() {
+
+		try {
+			Car brokencar = new Car("Broken", 0);
+		} catch (BadCarException ex) {
+			System.out.println(ex.getMessage() == "A car must have at least one door!");
+		}
+		Car c = null;
+		try {
+			c = new Car("Biggy", 7);
+		} catch (BadCarException ex) {
+			System.out.println("BUG! This must never happen!");
+		}
+		c.listDoors();
+		System.out.println(c.countOpenDoors() == 0);
+		c.changeAllDoors();
+		System.out.println(c.countOpenDoors() == 7);
+		c.listDoors();
+		c.changeAllDoors();
+		System.out.println(c.countOpenDoors() == 0);
+		try {
+			c.openOneDoor(8);
+		} catch (BadDoorException ex) {
+			System.out.println(ex.getMessage().equals("Door 8 does not exist!"));
+		}
+		try {
+			c.openOneDoor(3);
+		} catch (BadDoorException ex) {
+			System.out.println("BUG! This must never happen!");
+		}
+		System.out.println(c.countOpenDoors() == 1);
+
+		c.changeAllDoors();
+		System.out.println(c.countOpenDoors() == 6);
+		c.listDoors();
+		c.changeAllDoors();
+		System.out.println(c.countOpenDoors() == 1);
+		c.listDoors();
+		try {
+			c.replaceDoor(8);
+		} catch (BadDoorException ex) {
+
+			System.out.println(ex.getMessage().equals("Door 8 does not exist!"));
+		}
+		try {
+			c.replaceDoor(3);
+		} catch (BadDoorException ex) {
+			System.out.println("BUG! This must never happen!");
+		}
+		System.out.println(c.countOpenDoors() == 0);
+		c.listDoors();
+		c.changeAllDoors();
+		System.out.println(c.countOpenDoors() == 7);
+		c.listDoors();
+		c.replaceAllDoors();
+		System.out.println(c.countOpenDoors() == 0);
+		c.listDoors();
+		c.changeAllDoors();
+		System.out.println(c.countOpenDoors() == 7);
+		c.listDoors();
+		c.replaceManyDoors(4);
+		System.out.println(c.countOpenDoors() == 3);
+		c.listDoors();
+		try {
+			c.replaceManyDoors(20);
+		} catch (IndexOutOfBoundsException ex) {
+			System.out.println(ex.getMessage().equals("Index 7 out of bounds for length 7"));
+		}
+		System.out.println(c.countOpenDoors() == 0);
+		c.listDoors();
+		c.expandCar();
+		c.changeAllDoors();
+		System.out.println(c.countOpenDoors() == 9);
+		c.listDoors();
+	}
+}

lab/lab9/Question7/Door.java

@@ -0,0 +1,54 @@
+/*
+ * Author: CHEN Yongyuan (Walter) 1930006025 from OOP(1007)
+ * Date: 2022-04-21
+ * Description: This is the class of Door.
+ */
+
+public class Door {
+	/**
+	 * Indicator of whether the door is open or not. Default is closed
+	 */
+	private boolean isOpen;
+
+	/**
+	 * Constructor.
+	 */
+	public Door() {
+		isOpen = false;
+	}
+
+	/**
+	 * Get whether the door is open or not.
+	 *
+	 * @return true if the door is open, false otherwise
+	 */
+	public boolean isOpen() {
+		return isOpen;
+	}
+
+	/**
+	 * Open the door.
+	 */
+	public void open() {
+		isOpen = true;
+	}
+
+	/**
+	 * Close the door.
+	 */
+	public void close() {
+		isOpen = false;
+	}
+
+	/**
+	 * Test.
+	 */
+	public static void testDoor() {
+		Door d = new Door();
+		System.out.println(d.isOpen() == false);
+		d.close();
+		System.out.println(d.isOpen() == false);
+		d.open();
+		System.out.println(d.isOpen() == true);
+	}
+}

lab/lab9/Question7/Start.java

@@ -0,0 +1,21 @@
+/**
+ * Answer to questions.
+ *
+ * - Q4: What happends if you try to use am enhanced for loop?
+ *
+ * - A: The original doors will not be replace. When you use for (Door door :
+ * doors), JVM will copy the value to door (or copy the address). If you set
+ * door = new Door(), the new door will be assigned to that copied object,
+ * istead of the object in array.
+ *
+ * - Q5: What happends if you try to replace more doors than the car has?
+ *
+ * - A: It will throw ArrayIndexOutOfBoundsException.
+ *
+ */
+public class Start {
+	public static void main(String[] args) {
+		Door.testDoor();
+		Car.testCar();
+	}
+}