final project q4

finalproject/Question4/Borrower.java

@@ -0,0 +1,63 @@
+/*
+ * Author: CHEN Yongyuan (Walter) 1930006025 from OOP(1007)
+ * Date: 2022-04-25
+ * Description: This is the borrower class.
+ */
+
+public class Borrower extends User {
+	/**
+	 * Constructor.
+	 *
+	 * @param name Borrower's name
+	 * @param int  book number of books borrowed by user
+	 */
+	public Borrower(String name, int book) throws NotALenderException {
+		super(name, book);
+
+		// check
+		if (book < 0) {
+			throw new NotALenderException("A new borrower cannot lend books.");
+		}
+	}
+
+	/**
+	 * increase the number of books borrowed by the user.
+	 *
+	 * @param number Incrased number of books
+	 * @throws NotALenderException
+	 */
+	public void moreBook(int number) throws NotALenderException {
+		int newBook = getBook() + number;
+		if (number < 0 && newBook < 0) {
+			throw new NotALenderException("A borrower cannot lend " + (-newBook) + " book(s).");
+		}
+		setBook(newBook);
+	}
+
+	/**
+	 * Test.
+	 */
+	public static void testBorrower() {
+		try {
+			Borrower b = new Borrower("Bob", -1);
+		} catch (NotALenderException e) {
+			System.out.println(e.getMessage().equals("A new borrower cannot lend books."));
+		}
+		try {
+			Borrower b = new Borrower("Bob", 10);
+			System.out.println(b.getName() == "Bob");
+			System.out.println(b.getBook() == 10);
+			b.setBook(5);
+			System.out.println(b.getBook() == 5);
+			b.moreBook(2);
+			System.out.println(b.getBook() == 7);
+			b.moreBook(-2);
+			System.out.println(b.getBook() == 5);
+			b.moreBook(-5);
+			System.out.println(b.getBook() == 0);
+			b.moreBook(-1);
+		} catch (NotALenderException e) {
+			System.out.println(e.getMessage().equals("A borrower cannot lend 1 book(s)."));
+		}
+	}
+}