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CS2030S-Problem Set 5 Solved
. In Java, a Set is a Collection that does not contain duplicate elements (this is in contrast to a List which does allow duplicates). You are given the Point class below:
public class Point { private final int x; private final int y;
public Point(int x, int y) { this.x = x; this.y = y;
}
@Override
public String toString() { return "(" + this.x + ", " + this.y + ")";
}
}
(a) What is the output of the following program fragment executed in jshell?
List<Point> points = new ArrayList<>() points.add(new Point(1, 1)) points.add(new Point(1, 1)) points.indexOf(new Point(1, 1))
(b) By defining an appropriate overriding equals method, demonstrate how the indexOf method can now give the correct behaviour.
(c) What is the output of the following program fragment executed in jshell?
Point p = new Point(1, 1);
Point q = new Point(1, 1); p.equals(q)
Set<Point> set = new HashSet<>()
set.add(p) set.add(q) set
(d) Notice that although p.equals(q) returns true, the two points are considered distinct by HashSet. How do we ensure that only one point is maintained in the set?
Hint: Refer to the definition of the equals method in Object class
2. The Java Collection<E> interface extends the Iterable<E> interface with the following abstract method declared.
Iterator<E> iterator();
(a) Using the methods in the Iterator class, demonstrate how iteration is performed on a List, e.g.
List<Point> list = new ArrayList<>(); list.add(new Point(1, 1)); list.add(new Point(2, 2));
(b) How is the use of an Iterator object, different from the following
for (Point p : list) {
System.out.println(p);
}
3. What is the output of the following program fragment? Explain.
class A { static void f() throws Exception { try { throw new Exception(); } finally {
System.out.print("1");
}
}
static void g() throws Exception { System.out.print("2"); f();
System.out.print("3");
}
public static void main(String[] args) { try {
g();
} catch (Exception e) {
System.out.print("4");
}
}
}
4. You are given two classes MCQ and TFQ that implements a question-answer system:
• MCQ: multiple-choice questions comprising answers: A B C D E
• TFQ: true/false questions comprising answers: T F
class MCQ { String question; char answer;
public MCQ(String question) { this.question = question;
}
void getAnswer() {
System.out.print(question + " ");
answer = (new Scanner(System.in)).next().charAt(0);
if (answer < 'A' || answer > 'E') { throw new InvalidMCQException("Invalid MCQ answer"); }
}
}
class TFQ { String question; char answer;
public TFQ(String question) { this.question = question;
}
void getAnswer() {
System.out.print(question + " ");
answer = (new Scanner(System.in)).next().charAt(0);
if (answer != 'T' && answer != 'F') { throw new InvalidTFQException("Invalid TFQ answer"); }
}
}
In particular, an invalid answer to any of the questions will cause an exception (either InvalidMCQException or InvalidTFQException) to be thrown.
class InvalidMCQException extends IllegalArgumentException { public InvalidMCQException(String mesg) { super(mesg);
}
}
class InvalidTFQException extends IllegalArgumentException { public InvalidTFQException(String mesg) { super(mesg);
}
}
By employing the various object-oriented design principles, design a more general question-answer class QA that can take the place of both MCQ and TFQ types of questions (and possibly more in future, each with their own type of exceptions).
