Java Objective Questions and Answers

Given:
3. class A { }
4. class B extends A { }
5. public class ComingThru {
6. static String s = "-";
7. public static void main(String[] args) {
8. A[] aa = new A[2];
9. B[] ba = new B[2];
10. sifter(aa);
11. sifter(ba);
12. sifter(7);
13. System.out.println(s);
14. }
15. static void sifter(A[]... a2) { s += "1"; }
16. static void sifter(B[]... b1) { s += "2"; }
17. static void sifter(B[] b1) { s += "3"; }
18. static void sifter(Object o) { s += "4"; }
19. }
What is the result?

Given:
3. import java.io.*;
4. class Vehicle { }
5. class Wheels { }
6. class Car extends Vehicle implements Serializable { }
7. class Ford extends Car { }
8. class Dodge extends Car {
9. Wheels w = new Wheels();
10. }
Instances of which class(es) can be serialized? (Choose all that apply.)
A. Car
B. Ford
C. Dodge
D. Wheels
E. Vehicle

Given:
3. import java.util.regex.*;
4. public class Archie {
5. public static void main(String[] args) {
6. Pattern p = Pattern.compile(args[0]);
7. Matcher m = p.matcher(args[1]);
8. int count = 0;
9. while(m.find())
10. count++;
11. System.out.print(count);
12. }
13. }
And given the command line invocation:
java Archie "\d+" ab2c4d67
What is the result?

Given:
3. import java.util.*;
4. public class Looking {
5. public static void main(String[] args) {
6. String input = "1 2 a 3 45 6";
7. Scanner sc = new Scanner(input);
8. int x = 0;
9. do {
10. x = sc.nextInt();
11. System.out.print(x + " ");
12. } while (x!=0);
13. }
14. }
What is the result?

Given the proper import statement(s), and
13. PriorityQueue<String> pq = new PriorityQueue<String>();
14. pq.add("2");
15. pq.add("4");
16. System.out.print(pq.peek() + " ");
17. pq.offer("1");
18. pq.add("3");
19. pq.remove("1");
20. System.out.print(pq.poll() + " ");
21. if(pq.remove("2")) System.out.print(pq.poll() + " ");
22. System.out.println(pq.poll() + " " + pq.peek());
What is the result?

Given:
3. import java.util.*;
4. public class Mixup {
5. public static void main(String[] args) {
6. Object o = new Object();
7. // insert code here
8. s.add("o");
9. s.add(o);
10. }
11. }
And these three fragments:
I. Set s = new HashSet();
II. TreeSet s = new TreeSet();
III. LinkedHashSet s = new LinkedHashSet();
When fragments I, II, or III are inserted, independently, at line 7, which are true?
(Choose all that apply.)
A. Fragment I compiles
B. Fragment II compiles
C. Fragment III compiles
D. Fragment I executes without exception
E. Fragment II executes without exception
F. Fragment III executes without exception

Given:
3. import java.util.*;
4. class Turtle {
5. int size;
6. public Turtle(int s) { size = s; }
7. public boolean equals(Object o) { return (this.size == ((Turtle)o).size); }
8. // insert code here
9. }
10. public class TurtleTest {
11. public static void main(String[] args) {
12. LinkedHashSet<Turtle> t = new LinkedHashSet<Turtle>();
13. t.add(new Turtle(1)); t.add(new Turtle(2)); t.add(new Turtle(1));
14. System.out.println(t.size());
15. }
16. }
And these two fragments:
I. public int hashCode() { return size/5; }
II. // no hashCode method declared
If fragment I or II is inserted, independently, at line 8, which are true? (Choose all that apply.)
A. If fragment I is inserted, the output is 2
B. If fragment I is inserted, the output is 3
C. If fragment II is inserted, the output is 2
D. If fragment II is inserted, the output is 3
E. If fragment I is inserted, compilation fails
F. If fragment II is inserted, compilation fails

Given the proper import statement(s), and:
13. TreeSet<String> s = new TreeSet<String>();
14. TreeSet<String> subs = new TreeSet<String>();
15. s.add("a"); s.add("b"); s.add("c"); s.add("d"); s.add("e");
16.
17. subs = (TreeSet)s.subSet("b", true, "d", true);
18. s.add("g");
19. s.pollFirst();
20. s.pollFirst();
21. s.add("c2");
22. System.out.println(s.size() +" "+ subs.size());
Which are true? (Choose all that apply.)
A. The size of s is 4
B. The size of s is 5
C. The size of s is 7
D. The size of subs is 1
E. The size of subs is 2
F. The size of subs is 3
G. The size of subs is 4
H. An exception is thrown at runtime

Given:
3. import java.util.*;
4. public class Magellan {
5. public static void main(String[] args) {
6. TreeMap<String, String> myMap = new TreeMap<String, String>();
7. myMap.put("a", "apple"); myMap.put("d", "date");
8. myMap.put("f", "fig"); myMap.put("p", "pear");
9. System.out.println("1st after mango: " + // sop 1
10. myMap.higherKey("f"));
11. System.out.println("1st after mango: " + // sop 2
12. myMap.ceilingKey("f"));
13. System.out.println("1st after mango: " + // sop 3
14. myMap.floorKey("f"));
15. SortedMap<String, String> sub = new TreeMap<String, String>();
16. sub = myMap.tailMap("f");
17. System.out.println("1st after mango: " + // sop 4
18. sub.firstKey());
19. }
20. }
Which of the System.out.println statements will produce the output 1st after mango: p?

Which are true about a static nested class?

A. You must have a reference to an instance of the enclosing class in order to instantiate it
B. It does not have access to non-static members of the enclosing class
C. Its variables and methods must be static
D. If the outer class is named MyOuter, and the nested class is named MyInner, it can be
instantiated using new MyOuter.MyInner();
E. It must extend the enclosing class

Given:
class Boo {
Boo(String s) { }
Boo() { }
}
class Bar extends Boo {
Bar() { }
Bar(String s) {super(s);}
void zoo() {
// insert code here
}
}
Which create an anonymous inner class from within class Bar?
A. Boo f = new Boo(24) { };
B. Boo f = new Bar() { };
C. Boo f = new Boo() {String s; };
D. Bar f = new Boo(String s) { };
E. Boo f = new Boo.Bar(String s) { };

Given:
3. import java.util.*;
4. class Business { }
5. class Hotel extends Business { }
6. class Inn extends Hotel { }
7. public class Travel {
8. ArrayList&ltHotel&gt go() {
9. // insert code here
10. }
11. }
Which, inserted independently at line 9, will compile?

Given:
3. import java.util.*;
4. class Dog { int size; Dog(int s) { size = s; } }
5. public class FirstGrade {
6. public static void main(String[] args) {
7. TreeSet&ltInteger&gt i = new TreeSet&ltInteger&gt();
8. TreeSet&ltDog&gt d = new TreeSet&ltDog&gt();
9.
10. d.add(new Dog(1)); d.add(new Dog(2)); d.add(new Dog(1));
11. i.add(1); i.add(2); i.add(1);
12. System.out.println(d.size() + " " + i.size());
13. }
14. }
What is the result?

Which are true about a method-local inner class?
A. It must be marked final
B. It can be marked abstract
C. It can be marked public
D. It can be marked static
E. It can access private members of the enclosing class

Given:
1. public class TestObj {
2. public static void main(String[] args) {
3. Object o = new Object() {
4. public boolean equals(Object obj) {
5. return true;
6. }
7. }
8. System.out.println(o.equals("Fred"));
9. }
10. }
What is the result?