a4 close #6

assignment4/Question1/Course.java

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+/*
+ * Author: CHEN Yongyuan (Walter) 1930006025 from OOP(1007)
+ * Date: 2022-04-18
+ * Description: This is the Course class.
+ */
+
+public abstract class Course {
+	/**
+	 * The code of the course.
+	 */
+	private String code;
+
+	/**
+	 * The title of the course.
+	 */
+	private String title;
+
+	/**
+	 * The pre-requisite of the course.
+	 *
+	 * A course always has only one pre-requisite course and the pre-requisite
+	 * course cannot be null.
+	 *
+	 * @see Course
+	 */
+	private Course preRequisite;
+
+	/**
+	 * Constructor.
+	 *
+	 * @param code         The code of the course.
+	 * @param title        The title of the course.
+	 * @param preRequisite The pre-requisite of the course. If the pre-requisite
+	 *                     course is null, the constructor will print a message of
+	 *                     "pre-requisite course cannot be null!" and return
+	 *                     directly.
+	 */
+	public Course(String code, String title, Course preRequisite) {
+		if (preRequisite == null) {
+			System.out.println("pre-requisite course cannot be null!");
+			return;
+		}
+
+		this.code = code;
+		this.title = title;
+		this.preRequisite = preRequisite;
+	}
+
+	/**
+	 * Get the code of the course.
+	 *
+	 * @return The code of the course.
+	 */
+	public String getCode() {
+		return code;
+	}
+
+	/**
+	 * Get the title of the course.
+	 *
+	 * @return The title of the course.
+	 */
+	public String getTitle() {
+		return title;
+	}
+
+	/**
+	 * Get the pre-requisite of the course.
+	 *
+	 * @return The pre-requisite of the course.
+	 */
+	public Course getPreRequisite() {
+		return preRequisite;
+	}
+
+	/**
+	 * Indicate whether a course is required or not.
+	 *
+	 * One course could either be a required course or a elective course. Some
+	 * courses are required, while the others are not required.
+	 *
+	 * @return True if the course is required, false if the course is not required.
+	 */
+	public abstract boolean isRequired();
+
+	/**
+	 * Test.
+	 */
+	public static void testCourse() {
+		Course mr = new Course("CS101", "Intro to Java", null) {
+			@Override
+			public boolean isRequired() {
+				return true;
+			}
+		};
+		System.out.println(mr.getCode() == null);
+		System.out.println(mr.getTitle() == null);
+		System.out.println(mr.getPreRequisite() == null);
+		System.out.println(mr.isRequired() == true);
+
+		Course me = new Course("CS102", "Intro to Python", mr) {
+			@Override
+			public boolean isRequired() {
+				return false;
+			}
+		};
+		System.out.println(me.getCode() == "CS102");
+		System.out.println(me.getTitle() == "Intro to Python");
+		System.out.println(me.getPreRequisite() == mr);
+		System.out.println(me.isRequired() == false);
+
+	}
+}

assignment4/Question1/Start.java

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+/**
+ * Answer to the questions.
+ *
+ * - Q: What kinds of tests can you write inside the testCourse method?
+ *
+ * - A: You can inherit the Couse class to annonymous class and override the
+ * isRequired() method.
+ */
+
+public class Start {
+	public static void main(String[] args) {
+		Course.testCourse();
+	}
+}

assignment4/Question2/Course.java

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+/*
+ * Author: CHEN Yongyuan (Walter) 1930006025 from OOP(1007)
+ * Date: 2022-04-18
+ * Description: This is the Course class.
+ */
+
+public abstract class Course {
+	/**
+	 * The code of the course.
+	 */
+	private String code;
+
+	/**
+	 * The title of the course.
+	 */
+	private String title;
+
+	/**
+	 * The pre-requisite of the course.
+	 *
+	 * A course always has only one pre-requisite course and the pre-requisite
+	 * course cannot be null.
+	 *
+	 * @see Course
+	 */
+	private Course preRequisite;
+
+	/**
+	 * Constructor.
+	 *
+	 * @param code         The code of the course.
+	 * @param title        The title of the course.
+	 * @param preRequisite The pre-requisite of the course. If the pre-requisite
+	 *                     course is null, the constructor will print a message of
+	 *                     "pre-requisite course cannot be null!" and return
+	 *                     directly.
+	 */
+	public Course(String code, String title, Course preRequisite) {
+		if (preRequisite == null) {
+			System.out.println("pre-requisite course cannot be null!");
+			return;
+		}
+
+		this.code = code;
+		this.title = title;
+		this.preRequisite = preRequisite;
+	}
+
+	/**
+	 * Get the code of the course.
+	 *
+	 * @return The code of the course.
+	 */
+	public String getCode() {
+		return code;
+	}
+
+	/**
+	 * Get the title of the course.
+	 *
+	 * @return The title of the course.
+	 */
+	public String getTitle() {
+		return title;
+	}
+
+	/**
+	 * Get the pre-requisite of the course.
+	 *
+	 * @return The pre-requisite of the course.
+	 */
+	public Course getPreRequisite() {
+		return preRequisite;
+	}
+
+	/**
+	 * Indicate whether a course is required or not.
+	 *
+	 * One course could either be a required course or a elective course. Some
+	 * courses are required, while the others are not required.
+	 *
+	 * @return True if the course is required, false if the course is not required.
+	 */
+	public abstract boolean isRequired();
+
+	/**
+	 * Test.
+	 */
+	public static void testCourse() {
+		Course mr = new Course("CS101", "Intro to Java", null) {
+			@Override
+			public boolean isRequired() {
+				return true;
+			}
+		};
+		System.out.println(mr.getCode() == null);
+		System.out.println(mr.getTitle() == null);
+		System.out.println(mr.getPreRequisite() == null);
+		System.out.println(mr.isRequired() == true);
+
+		Course me = new Course("CS102", "Intro to Python", mr) {
+			@Override
+			public boolean isRequired() {
+				return false;
+			}
+		};
+		System.out.println(me.getCode() == "CS102");
+		System.out.println(me.getTitle() == "Intro to Python");
+		System.out.println(me.getPreRequisite() == mr);
+		System.out.println(me.isRequired() == false);
+
+	}
+}

assignment4/Question2/MajorRequired.java

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+/*
+ * Author: CHEN Yongyuan (Walter) 1930006025 from OOP(1007)
+ * Date: 2022-04-18
+ * Description: This is the MajorRequired class which is used to store the major and required courses.
+ */
+
+public class MajorRequired extends Course {
+	/**
+	 * Constructor.
+	 *
+	 * @param code         The code of the course.
+	 * @param title        The title of the course.
+	 * @param preRequisite The pre-requisite of the course. Type of MajorRequired
+	 *                     and cannot be null.
+	 */
+	public MajorRequired(String code, String title, MajorRequired preRequisite) {
+		super(code, title, preRequisite);
+	}
+
+	/**
+	 * MajorRequired course is required for all students.
+	 *
+	 * @return true
+	 */
+	@Override
+	public boolean isRequired() {
+		return true;
+	}
+
+	/**
+	 * Test.
+	 */
+	public static void testMajorRequired() {
+		MajorRequired mr1 = new MajorRequired("COMP3013", "Database Management System", null);
+		System.out.println(mr1.getCode() == null);
+		System.out.println(mr1.getTitle() == null);
+		System.out.println(mr1.getPreRequisite() == null);
+		System.out.println(mr1.isRequired() == true);
+
+		MajorRequired mr2 = new MajorRequired("COMP3013", "Database Management System", mr1);
+		System.out.println(mr2.getCode() == "COMP3013");
+		System.out.println(mr2.getTitle() == "Database Management System");
+		System.out.println(mr2.getPreRequisite() == mr1);
+		System.out.println(mr2.isRequired() == false);
+	}
+}

assignment4/Question2/Start.java

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+/**
+ * Answer to the questions.
+ *
+ * - Q: What kinds of tests can you write inside the testCourse method?
+ *
+ * - A: You can inherit the Couse class to annonymous class and override the
+ * isRequired() method.
+ *
+ * - Q: What kinds of tests can you write inside the testMajorRequired method?
+ *
+ * - A: You can first create a MajorRequired object with null preRequisite and
+ * do the test as normal.
+ */
+
+public class Start {
+	public static void main(String[] args) {
+		Course.testCourse();
+		MajorRequired.testMajorRequired();
+	}
+}

assignment4/Question3/Course.java

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+/*
+ * Author: CHEN Yongyuan (Walter) 1930006025 from OOP(1007)
+ * Date: 2022-04-18
+ * Description: This is the Course class.
+ */
+
+public abstract class Course {
+	/**
+	 * The code of the course.
+	 */
+	private String code;
+
+	/**
+	 * The title of the course.
+	 */
+	private String title;
+
+	/**
+	 * The pre-requisite of the course.
+	 *
+	 * A course always has only one pre-requisite course and the pre-requisite
+	 * course cannot be null.
+	 *
+	 * @see Course
+	 */
+	private Course preRequisite;
+
+	/**
+	 * Constructor.
+	 *
+	 * @param code         The code of the course.
+	 * @param title        The title of the course.
+	 * @param preRequisite The pre-requisite of the course. If the pre-requisite
+	 *                     course is null, the constructor will print a message of
+	 *                     "pre-requisite course cannot be null!" and return
+	 *                     directly.
+	 */
+	public Course(String code, String title, Course preRequisite) {
+		if (preRequisite == null) {
+			System.out.println("pre-requisite course cannot be null!");
+			return;
+		}
+
+		this.code = code;
+		this.title = title;
+		this.preRequisite = preRequisite;
+	}
+
+	/**
+	 * Get the code of the course.
+	 *
+	 * @return The code of the course.
+	 */
+	public String getCode() {
+		return code;
+	}
+
+	/**
+	 * Get the title of the course.
+	 *
+	 * @return The title of the course.
+	 */
+	public String getTitle() {
+		return title;
+	}
+
+	/**
+	 * Get the pre-requisite of the course.
+	 *
+	 * @return The pre-requisite of the course.
+	 */
+	public Course getPreRequisite() {
+		return preRequisite;
+	}
+
+	/**
+	 * Indicate whether a course is required or not.
+	 *
+	 * One course could either be a required course or a elective course. Some
+	 * courses are required, while the others are not required.
+	 *
+	 * @return True if the course is required, false if the course is not required.
+	 */
+	public abstract boolean isRequired();
+
+	/**
+	 * Test.
+	 */
+	public static void testCourse() {
+		Course mr = new Course("CS101", "Intro to Java", null) {
+			@Override
+			public boolean isRequired() {
+				return true;
+			}
+		};
+		System.out.println(mr.getCode() == null);
+		System.out.println(mr.getTitle() == null);
+		System.out.println(mr.getPreRequisite() == null);
+		System.out.println(mr.isRequired() == true);
+
+		Course me = new Course("CS102", "Intro to Python", mr) {
+			@Override
+			public boolean isRequired() {
+				return false;
+			}
+		};
+		System.out.println(me.getCode() == "CS102");
+		System.out.println(me.getTitle() == "Intro to Python");
+		System.out.println(me.getPreRequisite() == mr);
+		System.out.println(me.isRequired() == false);
+
+	}
+}

assignment4/Question3/MajorElective.java

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+/*
+ * Author: CHEN Yongyuan (Walter) 1930006025 from OOP(1007)
+ * Date: 2022-04-18
+ * Description: This is the MajorElective class which is elective for students.
+ */
+
+public class MajorElective extends Course {
+	/**
+	 * Constructor.
+	 *
+	 * @param code         The code of the course.
+	 * @param title        The title of the course.
+	 * @param preRequisite The pre-requisite of the course. Type of MajorElective
+	 *                     and cannot be null.
+	 */
+	public MajorElective(String code, String title, MajorElective preRequisite) {
+		super(code, title, preRequisite);
+	}
+
+	/**
+	 * MajorRequired course is elective for all students.
+	 *
+	 * @return false
+	 */
+	public boolean isRequired() {
+		return false;
+	}
+
+	/**
+	 * Test.
+	 */
+	public static void testMajorElective() {
+		MajorElective pre = new MajorElective("CSC108", "Intro to Programming", null);
+		System.out.println(pre.getCode() == null);
+		System.out.println(pre.getTitle() == null);
+		System.out.println(pre.getPreRequisite() == null);
+		System.out.println(pre.isRequired() == false);
+
+		MajorElective pre2 = new MajorElective("CSC108", "Intro to Programming", pre);
+		System.out.println(pre2.getCode() == "CSC108");
+		System.out.println(pre2.getTitle() == "Intro to Programming");
+		System.out.println(pre2.getPreRequisite() == pre);
+		System.out.println(pre2.isRequired() == false);
+	}
+}

assignment4/Question3/MajorRequired.java

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+/*
+ * Author: CHEN Yongyuan (Walter) 1930006025 from OOP(1007)
+ * Date: 2022-04-18
+ * Description: This is the MajorRequired class which is used to store the major and required courses.
+ */
+
+public class MajorRequired extends Course {
+	/**
+	 * Constructor.
+	 *
+	 * @param code         The code of the course.
+	 * @param title        The title of the course.
+	 * @param preRequisite The pre-requisite of the course. Type of MajorRequired
+	 *                     and cannot be null.
+	 */
+	public MajorRequired(String code, String title, MajorRequired preRequisite) {
+		super(code, title, preRequisite);
+	}
+
+	/**
+	 * MajorRequired course is required for all students.
+	 *
+	 * @return true
+	 */
+	@Override
+	public boolean isRequired() {
+		return true;
+	}
+
+	/**
+	 * Test.
+	 */
+	public static void testMajorRequired() {
+		MajorRequired mr1 = new MajorRequired("COMP3013", "Database Management System", null);
+		System.out.println(mr1.getCode() == null);
+		System.out.println(mr1.getTitle() == null);
+		System.out.println(mr1.getPreRequisite() == null);
+		System.out.println(mr1.isRequired() == true);
+
+		MajorRequired mr2 = new MajorRequired("COMP3013", "Database Management System", mr1);
+		System.out.println(mr2.getCode() == "COMP3013");
+		System.out.println(mr2.getTitle() == "Database Management System");
+		System.out.println(mr2.getPreRequisite() == mr1);
+		System.out.println(mr2.isRequired() == true);
+	}
+}

assignment4/Question3/Start.java

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+/**
+ * Answer to the questions.
+ *
+ * - Q: What kinds of tests can you write inside the testCourse method?
+ *
+ * - A: You can inherit the Couse class to annonymous class and override the
+ * isRequired() method.
+ *
+ * - Q: What kinds of tests can you write inside the testMajorRequired method?
+ *
+ * - A: You can first create a MajorRequired object with null preRequisite and
+ * do the test as normal.
+ *
+ * - Q: What kinds of tests can you write inside the testMajorElective method?
+ *
+ * - A: You can first create a MajorElective object with null preRequisite and
+ * do the test as normal.
+ */
+
+public class Start {
+	public static void main(String[] args) {
+		Course.testCourse();
+		MajorRequired.testMajorRequired();
+		MajorElective.testMajorElective();
+	}
+}

assignment4/Question4/Base.java

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+/*
+ * Author: CHEN Yongyuan (Walter) 1930006025 from OOP(1007)
+ * Date: 2022-04-18
+ * Description: This is the Base Class.
+ */
+
+public class Base {
+	private String code;
+	private String title;
+
+	/**
+	 * Constructor
+	 * 
+	 * @param code  The code of the course
+	 * @param title The title of the course
+	 */
+	public Base(String code, String title) {
+		this.code = code;
+		this.title = title;
+	}
+
+	/**
+	 * Getter of code
+	 *
+	 * @return The code of the course
+	 */
+	public String getCode() {
+		return code;
+	}
+
+	/**
+	 * Getter of title
+	 *
+	 * @return The title of the course
+	 */
+	public String getTitle() {
+		return title;
+	}
+
+	/**
+	 * Get the pre-requisite course. It will return itself.
+	 *
+	 * @return this
+	 */
+	public Base getPreRequisite() {
+		return this;
+	}
+
+	/**
+	 * Test.
+	 */
+	public static void testBase() {
+		Base base = new Base("COMP3013", "Database Management System");
+		System.out.println(base.getCode() == "COMP3013");
+		System.out.println(base.getTitle() == "Database Management System");
+		System.out.println(base.getPreRequisite() == base);
+	}
+}

assignment4/Question4/Course.java

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+/*
+ * Author: CHEN Yongyuan (Walter) 1930006025 from OOP(1007)
+ * Date: 2022-04-18
+ * Description: This is the Course class.
+ */
+
+public abstract class Course {
+	/**
+	 * The code of the course.
+	 */
+	private String code;
+
+	/**
+	 * The title of the course.
+	 */
+	private String title;
+
+	/**
+	 * The pre-requisite of the course.
+	 *
+	 * A course always has only one pre-requisite course and the pre-requisite
+	 * course cannot be null.
+	 *
+	 * @see Course
+	 */
+	private Course preRequisite;
+
+	/**
+	 * Constructor.
+	 *
+	 * @param code         The code of the course.
+	 * @param title        The title of the course.
+	 * @param preRequisite The pre-requisite of the course. If the pre-requisite
+	 *                     course is null, the constructor will print a message of
+	 *                     "pre-requisite course cannot be null!" and return
+	 *                     directly.
+	 */
+	public Course(String code, String title, Course preRequisite) {
+		if (preRequisite == null) {
+			System.out.println("pre-requisite course cannot be null!");
+			return;
+		}
+
+		this.code = code;
+		this.title = title;
+		this.preRequisite = preRequisite;
+	}
+
+	/**
+	 * Get the code of the course.
+	 *
+	 * @return The code of the course.
+	 */
+	public String getCode() {
+		return code;
+	}
+
+	/**
+	 * Get the title of the course.
+	 *
+	 * @return The title of the course.
+	 */
+	public String getTitle() {
+		return title;
+	}
+
+	/**
+	 * Get the pre-requisite of the course.
+	 *
+	 * @return The pre-requisite of the course.
+	 */
+	public Course getPreRequisite() {
+		return preRequisite;
+	}
+
+	/**
+	 * Indicate whether a course is required or not.
+	 *
+	 * One course could either be a required course or a elective course. Some
+	 * courses are required, while the others are not required.
+	 *
+	 * @return True if the course is required, false if the course is not required.
+	 */
+	public abstract boolean isRequired();
+
+	/**
+	 * Test.
+	 */
+	public static void testCourse() {
+		Course mr = new Course("CS101", "Intro to Java", null) {
+			@Override
+			public boolean isRequired() {
+				return true;
+			}
+		};
+		System.out.println(mr.getCode() == null);
+		System.out.println(mr.getTitle() == null);
+		System.out.println(mr.getPreRequisite() == null);
+		System.out.println(mr.isRequired() == true);
+
+		Course me = new Course("CS102", "Intro to Python", mr) {
+			@Override
+			public boolean isRequired() {
+				return false;
+			}
+		};
+		System.out.println(me.getCode() == "CS102");
+		System.out.println(me.getTitle() == "Intro to Python");
+		System.out.println(me.getPreRequisite() == mr);
+		System.out.println(me.isRequired() == false);
+
+	}
+}

assignment4/Question4/MajorElective.java

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+/*
+ * Author: CHEN Yongyuan (Walter) 1930006025 from OOP(1007)
+ * Date: 2022-04-18
+ * Description: This is the MajorElective class which is elective for students.
+ */
+
+public class MajorElective extends Course {
+	/**
+	 * Constructor.
+	 *
+	 * @param code         The code of the course.
+	 * @param title        The title of the course.
+	 * @param preRequisite The pre-requisite of the course. Type of MajorElective
+	 *                     and cannot be null.
+	 */
+	public MajorElective(String code, String title, MajorElective preRequisite) {
+		super(code, title, preRequisite);
+	}
+
+	/**
+	 * MajorRequired course is elective for all students.
+	 *
+	 * @return false
+	 */
+	public boolean isRequired() {
+		return false;
+	}
+
+	/**
+	 * Test.
+	 */
+	public static void testMajorElective() {
+		MajorElective pre = new MajorElective("CSC108", "Intro to Programming", null);
+		System.out.println(pre.getCode() == null);
+		System.out.println(pre.getTitle() == null);
+		System.out.println(pre.getPreRequisite() == null);
+		System.out.println(pre.isRequired() == false);
+
+		MajorElective pre2 = new MajorElective("CSC108", "Intro to Programming", pre);
+		System.out.println(pre2.getCode() == "CSC108");
+		System.out.println(pre2.getTitle() == "Intro to Programming");
+		System.out.println(pre2.getPreRequisite() == pre);
+		System.out.println(pre2.isRequired() == false);
+	}
+}

assignment4/Question4/MajorRequired.java

@@ -0,0 +1,46 @@
+/*
+ * Author: CHEN Yongyuan (Walter) 1930006025 from OOP(1007)
+ * Date: 2022-04-18
+ * Description: This is the MajorRequired class which is used to store the major and required courses.
+ */
+
+public class MajorRequired extends Course {
+	/**
+	 * Constructor.
+	 *
+	 * @param code         The code of the course.
+	 * @param title        The title of the course.
+	 * @param preRequisite The pre-requisite of the course. Type of MajorRequired
+	 *                     and cannot be null.
+	 */
+	public MajorRequired(String code, String title, MajorRequired preRequisite) {
+		super(code, title, preRequisite);
+	}
+
+	/**
+	 * MajorRequired course is required for all students.
+	 *
+	 * @return true
+	 */
+	@Override
+	public boolean isRequired() {
+		return true;
+	}
+
+	/**
+	 * Test.
+	 */
+	public static void testMajorRequired() {
+		MajorRequired mr1 = new MajorRequired("COMP3013", "Database Management System", null);
+		System.out.println(mr1.getCode() == null);
+		System.out.println(mr1.getTitle() == null);
+		System.out.println(mr1.getPreRequisite() == null);
+		System.out.println(mr1.isRequired() == true);
+
+		MajorRequired mr2 = new MajorRequired("COMP3013", "Database Management System", mr1);
+		System.out.println(mr2.getCode() == "COMP3013");
+		System.out.println(mr2.getTitle() == "Database Management System");
+		System.out.println(mr2.getPreRequisite() == mr1);
+		System.out.println(mr2.isRequired() == true);
+	}
+}

assignment4/Question4/Start.java

@@ -0,0 +1,27 @@
+/**
+ * Answer to the questions.
+ *
+ * - Q: What kinds of tests can you write inside the testCourse method?
+ *
+ * - A: You can inherit the Couse class to annonymous class and override the
+ * isRequired() method.
+ *
+ * - Q: What kinds of tests can you write inside the testMajorRequired method?
+ *
+ * - A: You can first create a MajorRequired object with null preRequisite and
+ * do the test as normal.
+ *
+ * - Q: What kinds of tests can you write inside the testMajorElective method?
+ *
+ * - A: You can first create a MajorElective object with null preRequisite and
+ * do the test as normal.
+ */
+
+public class Start {
+	public static void main(String[] args) {
+		Course.testCourse();
+		MajorRequired.testMajorRequired();
+		MajorElective.testMajorElective();
+		Base.testBase();
+	}
+}

assignment4/Question5/Base.java

@@ -0,0 +1,58 @@
+/*
+ * Author: CHEN Yongyuan (Walter) 1930006025 from OOP(1007)
+ * Date: 2022-04-18
+ * Description: This is the Base Class.
+ */
+
+public class Base implements Learnable {
+	private String code;
+	private String title;
+
+	/**
+	 * Constructor
+	 * 
+	 * @param code  The code of the course
+	 * @param title The title of the course
+	 */
+	public Base(String code, String title) {
+		this.code = code;
+		this.title = title;
+	}
+
+	/**
+	 * Getter of code
+	 *
+	 * @return The code of the course
+	 */
+	public String getCode() {
+		return code;
+	}
+
+	/**
+	 * Getter of title
+	 *
+	 * @return The title of the course
+	 */
+	public String getTitle() {
+		return title;
+	}
+
+	/**
+	 * Get the pre-requisite course. It will return itself.
+	 *
+	 * @return this
+	 */
+	public Learnable getPreRequisite() {
+		return this;
+	}
+
+	/**
+	 * Test.
+	 */
+	public static void testBase() {
+		Base base = new Base("COMP3013", "Database Management System");
+		System.out.println(base.getCode() == "COMP3013");
+		System.out.println(base.getTitle() == "Database Management System");
+		System.out.println(base.getPreRequisite() == base);
+	}
+}

assignment4/Question5/Course.java

@@ -0,0 +1,113 @@
+/*
+ * Author: CHEN Yongyuan (Walter) 1930006025 from OOP(1007)
+ * Date: 2022-04-18
+ * Description: This is the Course class.
+ */
+
+public abstract class Course implements Learnable {
+	/**
+	 * The code of the course.
+	 */
+	private String code;
+
+	/**
+	 * The title of the course.
+	 */
+	private String title;
+
+	/**
+	 * The pre-requisite of the course.
+	 *
+	 * A course always has only one pre-requisite course and the pre-requisite
+	 * course cannot be null.
+	 *
+	 * @see Course
+	 */
+	private Learnable preRequisite;
+
+	/**
+	 * Constructor.
+	 *
+	 * @param code         The code of the course.
+	 * @param title        The title of the course.
+	 * @param preRequisite The pre-requisite of the course. If the pre-requisite
+	 *                     course is null, the constructor will print a message of
+	 *                     "pre-requisite course cannot be null!" and return
+	 *                     directly.
+	 */
+	public Course(String code, String title, Learnable preRequisite) {
+		if (preRequisite == null) {
+			System.out.println("pre-requisite course cannot be null!");
+			return;
+		}
+
+		this.code = code;
+		this.title = title;
+		this.preRequisite = preRequisite;
+	}
+
+	/**
+	 * Get the code of the course.
+	 *
+	 * @return The code of the course.
+	 */
+	public String getCode() {
+		return code;
+	}
+
+	/**
+	 * Get the title of the course.
+	 *
+	 * @return The title of the course.
+	 */
+	public String getTitle() {
+		return title;
+	}
+
+	/**
+	 * Get the pre-requisite of the course.
+	 *
+	 * @return The pre-requisite of the course.
+	 */
+	public Learnable getPreRequisite() {
+		return preRequisite;
+	}
+
+	/**
+	 * Indicate whether a course is required or not.
+	 *
+	 * One course could either be a required course or a elective course. Some
+	 * courses are required, while the others are not required.
+	 *
+	 * @return True if the course is required, false if the course is not required.
+	 */
+	public abstract boolean isRequired();
+
+	/**
+	 * Test.
+	 */
+	public static void testCourse() {
+		Course mr = new Course("CS101", "Intro to Java", null) {
+			@Override
+			public boolean isRequired() {
+				return true;
+			}
+		};
+		System.out.println(mr.getCode() == null);
+		System.out.println(mr.getTitle() == null);
+		System.out.println(mr.getPreRequisite() == null);
+		System.out.println(mr.isRequired() == true);
+
+		Course me = new Course("CS102", "Intro to Python", mr) {
+			@Override
+			public boolean isRequired() {
+				return false;
+			}
+		};
+		System.out.println(me.getCode() == "CS102");
+		System.out.println(me.getTitle() == "Intro to Python");
+		System.out.println(me.getPreRequisite() == mr);
+		System.out.println(me.isRequired() == false);
+
+	}
+}

assignment4/Question5/Learnable.java

@@ -0,0 +1,13 @@
+/*
+ * Author: CHEN Yongyuan (Walter) 1930006025 from OOP(1007)
+ * Date: 2022-04-18
+ * Description: This is the Learnable interface.
+ */
+
+public interface Learnable {
+	public String getCode();
+
+	public String getTitle();
+
+	public Learnable getPreRequisite();
+}

assignment4/Question5/MajorElective.java

@@ -0,0 +1,56 @@
+/*
+ * Author: CHEN Yongyuan (Walter) 1930006025 from OOP(1007)
+ * Date: 2022-04-18
+ * Description: This is the MajorElective class which is elective for students.
+ */
+
+public class MajorElective extends Course {
+	/**
+	 * Constructor.
+	 *
+	 * @param code         The code of the course.
+	 * @param title        The title of the course.
+	 * @param preRequisite The pre-requisite of the course. Type of MajorElective
+	 *                     and cannot be null.
+	 */
+	public MajorElective(String code, String title, Learnable preRequisite) {
+		super(code, title, preRequisite);
+	}
+
+	/**
+	 * MajorRequired course is elective for all students.
+	 *
+	 * @return false
+	 */
+	public boolean isRequired() {
+		return false;
+	}
+
+	/**
+	 * Test.
+	 */
+	public static void testMajorElective() {
+		MajorElective pre = new MajorElective("CSC108", "Intro to Programming", null);
+		System.out.println(pre.getCode() == null);
+		System.out.println(pre.getTitle() == null);
+		System.out.println(pre.getPreRequisite() == null);
+		System.out.println(pre.isRequired() == false);
+
+		MajorElective pre2 = new MajorElective("CSC108", "Intro to Programming", pre);
+		System.out.println(pre2.getCode() == "CSC108");
+		System.out.println(pre2.getTitle() == "Intro to Programming");
+		System.out.println(pre2.getPreRequisite() == pre);
+		System.out.println(pre2.isRequired() == false);
+
+		Base base = new Base("COMP4023", "Software Engineering");
+		System.out.println(base.getCode() == "COMP4023");
+		System.out.println(base.getTitle() == "Software Engineering");
+		System.out.println(base.getPreRequisite() == base);
+
+		MajorElective me = new MajorElective("CSC123", "Big Data", base);
+		System.out.println(me.getCode() == "CSC123");
+		System.out.println(me.getTitle() == "Big Data");
+		System.out.println(me.getPreRequisite() == base);
+		System.out.println(me.isRequired() == false);
+	}
+}

assignment4/Question5/MajorRequired.java

@@ -0,0 +1,57 @@
+/*
+ * Author: CHEN Yongyuan (Walter) 1930006025 from OOP(1007)
+ * Date: 2022-04-18
+ * Description: This is the MajorRequired class which is used to store the major and required courses.
+ */
+
+public class MajorRequired extends Course {
+	/**
+	 * Constructor.
+	 *
+	 * @param code         The code of the course.
+	 * @param title        The title of the course.
+	 * @param preRequisite The pre-requisite of the course. Type of MajorRequired
+	 *                     and cannot be null.
+	 */
+	public MajorRequired(String code, String title, Learnable preRequisite) {
+		super(code, title, preRequisite);
+	}
+
+	/**
+	 * MajorRequired course is required for all students.
+	 *
+	 * @return true
+	 */
+	@Override
+	public boolean isRequired() {
+		return true;
+	}
+
+	/**
+	 * Test.
+	 */
+	public static void testMajorRequired() {
+		MajorRequired mr1 = new MajorRequired("COMP3013", "Database Management System", null);
+		System.out.println(mr1.getCode() == null);
+		System.out.println(mr1.getTitle() == null);
+		System.out.println(mr1.getPreRequisite() == null);
+		System.out.println(mr1.isRequired() == true);
+
+		MajorRequired mr2 = new MajorRequired("COMP3013", "Database Management System", mr1);
+		System.out.println(mr2.getCode() == "COMP3013");
+		System.out.println(mr2.getTitle() == "Database Management System");
+		System.out.println(mr2.getPreRequisite() == mr1);
+		System.out.println(mr2.isRequired() == true);
+
+		Base base = new Base("COMP4023", "Software Engineering");
+		System.out.println(base.getCode() == "COMP4023");
+		System.out.println(base.getTitle() == "Software Engineering");
+		System.out.println(base.getPreRequisite() == base);
+
+		MajorRequired mr3 = new MajorRequired("COMP4101", "Quality Assurance", base);
+		System.out.println(mr3.getCode() == "COMP4101");
+		System.out.println(mr3.getTitle() == "Quality Assurance");
+		System.out.println(mr3.getPreRequisite() == base);
+		System.out.println(mr3.isRequired() == true);
+	}
+}

assignment4/Question5/Start.java

@@ -0,0 +1,27 @@
+/**
+ * Answer to the questions.
+ *
+ * - Q: What kinds of tests can you write inside the testCourse method?
+ *
+ * - A: You can inherit the Couse class to annonymous class and override the
+ * isRequired() method.
+ *
+ * - Q: What kinds of tests can you write inside the testMajorRequired method?
+ *
+ * - A: You can first create a MajorRequired object with null preRequisite and
+ * do the test as normal.
+ *
+ * - Q: What kinds of tests can you write inside the testMajorElective method?
+ *
+ * - A: You can first create a MajorElective object with null preRequisite and
+ * do the test as normal.
+ */
+
+public class Start {
+	public static void main(String[] args) {
+		Course.testCourse();
+		MajorRequired.testMajorRequired();
+		MajorElective.testMajorElective();
+		Base.testBase();
+	}
+}

assignment4/Question6/Base.java

@@ -0,0 +1,58 @@
+/*
+ * Author: CHEN Yongyuan (Walter) 1930006025 from OOP(1007)
+ * Date: 2022-04-18
+ * Description: This is the Base Class.
+ */
+
+public class Base implements Learnable {
+	private String code;
+	private String title;
+
+	/**
+	 * Constructor
+	 * 
+	 * @param code  The code of the course
+	 * @param title The title of the course
+	 */
+	public Base(String code, String title) {
+		this.code = code;
+		this.title = title;
+	}
+
+	/**
+	 * Getter of code
+	 *
+	 * @return The code of the course
+	 */
+	public String getCode() {
+		return code;
+	}
+
+	/**
+	 * Getter of title
+	 *
+	 * @return The title of the course
+	 */
+	public String getTitle() {
+		return title;
+	}
+
+	/**
+	 * Get the pre-requisite course. It will return itself.
+	 *
+	 * @return this
+	 */
+	public Learnable getPreRequisite() {
+		return this;
+	}
+
+	/**
+	 * Test.
+	 */
+	public static void testBase() {
+		Base base = new Base("COMP3013", "Database Management System");
+		System.out.println(base.getCode() == "COMP3013");
+		System.out.println(base.getTitle() == "Database Management System");
+		System.out.println(base.getPreRequisite() == base);
+	}
+}

assignment4/Question6/Course.java

@@ -0,0 +1,113 @@
+/*
+ * Author: CHEN Yongyuan (Walter) 1930006025 from OOP(1007)
+ * Date: 2022-04-18
+ * Description: This is the Course class.
+ */
+
+public abstract class Course implements Learnable {
+	/**
+	 * The code of the course.
+	 */
+	private String code;
+
+	/**
+	 * The title of the course.
+	 */
+	private String title;
+
+	/**
+	 * The pre-requisite of the course.
+	 *
+	 * A course always has only one pre-requisite course and the pre-requisite
+	 * course cannot be null.
+	 *
+	 * @see Course
+	 */
+	private Learnable preRequisite;
+
+	/**
+	 * Constructor.
+	 *
+	 * @param code         The code of the course.
+	 * @param title        The title of the course.
+	 * @param preRequisite The pre-requisite of the course. If the pre-requisite
+	 *                     course is null, the constructor will print a message of
+	 *                     "pre-requisite course cannot be null!" and return
+	 *                     directly.
+	 */
+	public Course(String code, String title, Learnable preRequisite) {
+		if (preRequisite == null) {
+			System.out.println("pre-requisite course cannot be null!");
+			return;
+		}
+
+		this.code = code;
+		this.title = title;
+		this.preRequisite = preRequisite;
+	}
+
+	/**
+	 * Get the code of the course.
+	 *
+	 * @return The code of the course.
+	 */
+	public String getCode() {
+		return code;
+	}
+
+	/**
+	 * Get the title of the course.
+	 *
+	 * @return The title of the course.
+	 */
+	public String getTitle() {
+		return title;
+	}
+
+	/**
+	 * Get the pre-requisite of the course.
+	 *
+	 * @return The pre-requisite of the course.
+	 */
+	public Learnable getPreRequisite() {
+		return preRequisite;
+	}
+
+	/**
+	 * Indicate whether a course is required or not.
+	 *
+	 * One course could either be a required course or a elective course. Some
+	 * courses are required, while the others are not required.
+	 *
+	 * @return True if the course is required, false if the course is not required.
+	 */
+	public abstract boolean isRequired();
+
+	/**
+	 * Test.
+	 */
+	public static void testCourse() {
+		Course mr = new Course("CS101", "Intro to Java", null) {
+			@Override
+			public boolean isRequired() {
+				return true;
+			}
+		};
+		System.out.println(mr.getCode() == null);
+		System.out.println(mr.getTitle() == null);
+		System.out.println(mr.getPreRequisite() == null);
+		System.out.println(mr.isRequired() == true);
+
+		Course me = new Course("CS102", "Intro to Python", mr) {
+			@Override
+			public boolean isRequired() {
+				return false;
+			}
+		};
+		System.out.println(me.getCode() == "CS102");
+		System.out.println(me.getTitle() == "Intro to Python");
+		System.out.println(me.getPreRequisite() == mr);
+		System.out.println(me.isRequired() == false);
+
+	}
+}

assignment4/Question6/Learnable.java

@@ -0,0 +1,13 @@
+/*
+ * Author: CHEN Yongyuan (Walter) 1930006025 from OOP(1007)
+ * Date: 2022-04-18
+ * Description: This is the Learnable interface.
+ */
+
+public interface Learnable {
+	public String getCode();
+
+	public String getTitle();
+
+	public Learnable getPreRequisite();
+}

assignment4/Question6/MajorElective.java

@@ -0,0 +1,56 @@
+/*
+ * Author: CHEN Yongyuan (Walter) 1930006025 from OOP(1007)
+ * Date: 2022-04-18
+ * Description: This is the MajorElective class which is elective for students.
+ */
+
+public class MajorElective extends Course {
+	/**
+	 * Constructor.
+	 *
+	 * @param code         The code of the course.
+	 * @param title        The title of the course.
+	 * @param preRequisite The pre-requisite of the course. Type of MajorElective
+	 *                     and cannot be null.
+	 */
+	public MajorElective(String code, String title, Learnable preRequisite) {
+		super(code, title, preRequisite);
+	}
+
+	/**
+	 * MajorRequired course is elective for all students.
+	 *
+	 * @return false
+	 */
+	public boolean isRequired() {
+		return false;
+	}
+
+	/**
+	 * Test.
+	 */
+	public static void testMajorElective() {
+		MajorElective pre = new MajorElective("CSC108", "Intro to Programming", null);
+		System.out.println(pre.getCode() == null);
+		System.out.println(pre.getTitle() == null);
+		System.out.println(pre.getPreRequisite() == null);
+		System.out.println(pre.isRequired() == false);
+
+		MajorElective pre2 = new MajorElective("CSC108", "Intro to Programming", pre);
+		System.out.println(pre2.getCode() == "CSC108");
+		System.out.println(pre2.getTitle() == "Intro to Programming");
+		System.out.println(pre2.getPreRequisite() == pre);
+		System.out.println(pre2.isRequired() == false);
+
+		Base base = new Base("COMP4023", "Software Engineering");
+		System.out.println(base.getCode() == "COMP4023");
+		System.out.println(base.getTitle() == "Software Engineering");
+		System.out.println(base.getPreRequisite() == base);
+
+		MajorElective me = new MajorElective("CSC123", "Big Data", base);
+		System.out.println(me.getCode() == "CSC123");
+		System.out.println(me.getTitle() == "Big Data");
+		System.out.println(me.getPreRequisite() == base);
+		System.out.println(me.isRequired() == false);
+	}
+}

assignment4/Question6/MajorRequired.java

@@ -0,0 +1,57 @@
+/*
+ * Author: CHEN Yongyuan (Walter) 1930006025 from OOP(1007)
+ * Date: 2022-04-18
+ * Description: This is the MajorRequired class which is used to store the major and required courses.
+ */
+
+public class MajorRequired extends Course {
+	/**
+	 * Constructor.
+	 *
+	 * @param code         The code of the course.
+	 * @param title        The title of the course.
+	 * @param preRequisite The pre-requisite of the course. Type of MajorRequired
+	 *                     and cannot be null.
+	 */
+	public MajorRequired(String code, String title, Learnable preRequisite) {
+		super(code, title, preRequisite);
+	}
+
+	/**
+	 * MajorRequired course is required for all students.
+	 *
+	 * @return true
+	 */
+	@Override
+	public boolean isRequired() {
+		return true;
+	}
+
+	/**
+	 * Test.
+	 */
+	public static void testMajorRequired() {
+		MajorRequired mr1 = new MajorRequired("COMP3013", "Database Management System", null);
+		System.out.println(mr1.getCode() == null);
+		System.out.println(mr1.getTitle() == null);
+		System.out.println(mr1.getPreRequisite() == null);
+		System.out.println(mr1.isRequired() == true);
+
+		MajorRequired mr2 = new MajorRequired("COMP3013", "Database Management System", mr1);
+		System.out.println(mr2.getCode() == "COMP3013");
+		System.out.println(mr2.getTitle() == "Database Management System");
+		System.out.println(mr2.getPreRequisite() == mr1);
+		System.out.println(mr2.isRequired() == true);
+
+		Base base = new Base("COMP4023", "Software Engineering");
+		System.out.println(base.getCode() == "COMP4023");
+		System.out.println(base.getTitle() == "Software Engineering");
+		System.out.println(base.getPreRequisite() == base);
+
+		MajorRequired mr3 = new MajorRequired("COMP4101", "Quality Assurance", base);
+		System.out.println(mr3.getCode() == "COMP4101");
+		System.out.println(mr3.getTitle() == "Quality Assurance");
+		System.out.println(mr3.getPreRequisite() == base);
+		System.out.println(mr3.isRequired() == true);
+	}
+}

assignment4/Question6/ManyCourses.java

@@ -0,0 +1,51 @@
+/*
+ * Author: CHEN Yongyuan (Walter) 1930006025 from OOP(1007)
+ * Date: 2022-04-18
+ * Description: This is the ManyCourses class.
+ */
+
+import java.util.ArrayList;
+
+public class ManyCourses {
+	private ArrayList<Learnable> courses;
+
+	/**
+	 * Constructor.
+	 */
+	public ManyCourses() {
+		courses = new ArrayList<Learnable>();
+	}
+
+	/**
+	 * Add a course to the list.
+	 *
+	 * @param course
+	 */
+	public void addCourse(Learnable c) {
+		courses.add(c);
+	}
+
+	/**
+	 * Prints on the screen the course code and title.
+	 */
+	public void listCourses() {
+		for (Learnable c : courses) {
+			System.out.println(
+					String.format("%s, %s", c.getCode(), c.getTitle()));
+		}
+	}
+
+	/**
+	 * Test.
+	 */
+	public static void testManyCourses() {
+		Base b = new Base("DS1001", "EntryCourse");
+		MajorRequired mr1 = new MajorRequired("DS200X", "OOP", b);
+		MajorElective me1 = new MajorElective("DS300X", "Data Mining", mr1);
+		ManyCourses mc = new ManyCourses();
+		mc.addCourse(b);
+		mc.addCourse(mr1);
+		mc.addCourse(me1);
+		mc.listCourses();
+	}
+}

assignment4/Question6/Start.java

@@ -0,0 +1,28 @@
+/**
+ * Answer to the questions.
+ *
+ * - Q: What kinds of tests can you write inside the testCourse method?
+ *
+ * - A: You can inherit the Couse class to annonymous class and override the
+ * isRequired() method.
+ *
+ * - Q: What kinds of tests can you write inside the testMajorRequired method?
+ *
+ * - A: You can first create a MajorRequired object with null preRequisite and
+ * do the test as normal.
+ *
+ * - Q: What kinds of tests can you write inside the testMajorElective method?
+ *
+ * - A: You can first create a MajorElective object with null preRequisite and
+ * do the test as normal.
+ */
+
+public class Start {
+	public static void main(String[] args) {
+		Course.testCourse();
+		MajorRequired.testMajorRequired();
+		MajorElective.testMajorElective();
+		Base.testBase();
+		ManyCourses.testManyCourses();
+	}
+}