Java Programming Questions and Answers

Consider the following code:

1. public class ThreadOrder {

2. static int count=0;

3. public static void main(String[] args) {

4. Counter ct = new Counter();

5. Tracker trk1 = new Tracker(ct, "thread one");

6. Tracker trk2 = new Tracker(ct, "thread two");

7. trk1.start();

8. trk2.start();

9. }

10.}

11. class Tracker extends Thread {

12. Counter ct;

13. String message;

14. Tracker(Counter ct, String msg) {

15. this.ct = ct;

16. message = msg;

17. }

18. public void run() {

19. System.out.println(message);

20. }

21. }

22. class Counter {

23. private int count=0;

24. public int nextCounter() {

25. synchronized(this) {

26. count++;

27. return count;

28. }

29. }

30. }

What would be the output of this code fragment?

Which of the following is a method of the Object class?

Which of the following methods guarantee putting a thread out of the running state?

Which of the following is an invalid Thread constructor?

Consider the following code fragment:

Integer w1 = new Integer(2);

Integer w2 = new Integer(2);

if(w1 == w2)

{

System.out.println("w1 is equal to w2!");

}

else

{

System.out.println("w1 is not equal to w2!");

}

What is the output of this code?

Consider the following code fragment:

1. ArrayList list = new ArrayList();

2. list.add(new ObjectOne());

3. list.add(new ObjectOne());

4. list.add(new ObjectOne());

5. Collections.sort(list);

6. class ObjectOne {

7. private int x = 0;

8. private int y = 0;

9. }

What is the output of this code fragment?

Which of the following is an illegal line of code?

Which of the following collections can you use to store key-value pairs and is thread safe?

Consider the following code fragment:

1. import java.io.*;

2. class MyClass{

3. public static void main(String[] args) throws IOException {

4. NumberStore ns = new NumberStore();

5. System.out.println("The number: " + ns.getInteger());

6. ns.setInteger(10);

7. System.out.println("The number: " + ns.getInteger());

8. }

9. }

10. class NumberStore {

11. int i =5;

12. public void setInteger(Integer x){

13. System.out.println("The number passed in is: " + x);

14. i = x;

15. }

16. public int getInteger( ){

17. return i;

18. }

19.}

What is the output?

Consider the following code fragment:

1. ArrayList list = new ArrayList();

2. list.add(new Integer(1));

3. list.add(new Integer(2));

4. list.add(new Integer(3));

5. Iterator itr = list.iterator();

6. for(Integer wij:list){

7. System.out.println("number: " + wij);

8. }

What is the output from this code fragment?