Description
- 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 + “)”;
}
}
- 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))
- By defining an appropriate overriding equals method, demonstrate how the indexOf method can now give the correct behaviour.
- 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
- Notice that although 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
- The Java Collection<E> interface extends the Iterable<E> interface with the following abstract method declared.
Iterator<E> iterator();
- 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));
- How is the use of an Iterator object, different from the following
for (Point p : list) {
System.out.println(p);
}
- 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”);
}
}
}
- 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).
