190. Given: 

1. import java.util.*； 

2. public class WrappedString{ 

3. private String s；

 4. public WrappedString(String s){this.s = s；} 

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

 6. HashSet＜Object＞ hs = new HashSet＜Object＞()； 

7. WrappedString ws1 = new WrappedString("aardvark")；

 8. WrappedString ws2 = new WrappedString("aardvark")； 

9. String s1 = new String("aardvark")； 

10. String s2 = new String("aardvark")；

11. hs.add(ws1)； hs.add(ws2)； hs.add(s1)； hs.add(s2)； 

12. System.out.println(hs.size())； }} 

What is the result?
(A) 0
(B) 1
(C) 2
(D) 3
(E) 4

185. Given: 1. public class Person{ 2. private String name；  3. public Person(String name){this.name = name；} 4. public boolean equals(Person p){ 5. return p.name.equals(this.name)； 6. } 7. } Which statement is true? (A) The equals method does NOT properly override the Object.equals method. (B) Compilation fails because the private attribute p.name cannot be accessed in line 5. (C) To work correctly with hash-based data structures, this class must also implement the hashCode method. (D) When adding Person objects to a java.util.Set collection, the equals method in line 4 will prevent duplicates.

複選題186. Which two statements are true about the hashCode method? (Choose two.) (A) The hashCode method for a given class can be used to test for object equality and object inequality for that class. (B) The hashCode method is used by the java.util.SortedSet collection class to order the elements within that set. (C) The hashCode method for a given class can be used to test for object inequality, but NOT object equality, for that class. (D) The only important characteristic of the values returned by a hashCode method is that the distribution of values must follow a Gaussian distribution. (E) The hashCode method is used by the java.util.HashSet collection class to group the elements within that set into hash buckets for swift retrieval.

187. Given: 1. public class Score implements Comparable＜Score＞{ 2. private int wins, losses； 3. public Score(int w, int l){wins = w； losses = l；} 4. public int getWins(){return wins；} 5. public int getLosses(){return losses；} 6. public String toString(){ 7. return "＜" + wins + "," + losses + "＞"； 8. } 9. //insert code here 10. } Which method will complete this class? (A) public int compareTo(Object o){/* more code here */} (B) public int compareTo(Score other){/* more code here */} (C) public int compare(Score s1, Score s2){/* more code here */} (D) public int compare(Object o1, Object o2){/* more code here */}

189. Given: 23. Object[] myObjects = { 24. new Integer(12), 25. new String("foo"), 26. new Integer(5), 27. new Boolean(true) 28. }； 29. Arrays.sort(myObjects)； 30. for(int i=0； i＜myObjects.length； i++){ 31. System.out.print(myObjects[i].toString())； 32. System.out.print(" ")； 33. } What is the result? (A) Compilation fails due to an error in line 23. (B) Compilation fails due to an error in line 29. (C) A ClassCastException occurs in line 29. (D) A ClassCastException occurs in line 31. (E) The value of all four objects prints in natural order.

複選題192. Given: 3. import java.util.*； 4. public class G1{ 5. public void takeList(List＜? extends String＞ list){ 6. //insert code here 7. } 8. } Which three code fragments, inserted independently at line 6, will compile? (Choose three.) (A) list.add("foo")； (B) Object o = list； (C) String s = list.get(0)； (D) list = new ArrayList＜String＞()； (E) list = new ArrayList＜Object＞()；

193. Given that the elements of a PriorityQueue are ordered according to natural ordering, and: 2. import java.util.*； 3. public class GetInLine{ 4. public static void main(String[] args){ 5. PriorityQueue＜String＞ pq = new PriorityQueue＜String＞()； 6. pq.add("banana")； 7. pq.add("pear")； 8. pq.add("apple")； 9. System.out.println(pq.poll() + " " + pq.peek())； 10. } 11. } What is the result? (A) apple pear (B) banana pear (C) apple apple (D) apple banana (E) banana banana

194. Given:        enum Example{ONE, TWO, THREE} Which statement is true? (A) The expressions (ONE == ONE) and ONE .equals(ONE) are both guaranteed to be true. (B) The expression (ONE ＜ TWO) is guaranteed to be true and ONE.compareTo(TWO) is guaranteed to be less than one. (C) The Example values cannot be used in a raw javautil.HashMap； instead, the programmer must use a java.util.EnumMap. (D) The Example values can be used in a java.util.SortedSet, but the set will NOT be sorted because enumerated types do NOT implement java.lang.Comparable.

195. Given: 3. import java.util.*； 4. public class Mapit{ 5. public static void main(String[] args){ 6. Set＜Integer＞ set = new HashSet＜Integer＞()； 7. Integer i1 = 45； 8. Integer i2 = 46； 9. set.add(i1)； 10. set.add(i1)； 11. set.add(i2)； System.out.print(set.size() + " ")； 12. set.remove(i1)； System.out.print(set.size() + " ")； 13. i2 = 47； 14. set.remove(i2)； System.out.print(set.size() + " ")； 15. } 16. } What is the result? (A) 2 1 0 (B) 2 1 1 (C) 3 2 1 (D) 3 2 2 (E) Compilation fails.

196. Given: 34. HashMap props = new HashMap()； 35. props.put("key45", "some value")； 36. props.put("keyl2", "some other value")； 37. props.put("key39", "yet another value")； 38. Set s = props.keySet()； 39. //insert code here What inserted at line 39, will sort the keys in the props HashMap? (A) Arrays.sort(s)； (B) s = new TreeSet(s)； (C) Collections.sort(s)； (D) s = new SortedSet(s)；

197. Given: 11. public static Collection get(){ 12. Collection sorted = new LinkedList()； 13. sorted.add("B")； sorted.add("C")； sorted.add("A")； 14. return sorted； 15. } 16. public static void main(String[] args){ 17. for(Object obj : get()){ 18. System.out.print(obj + ", ")； 19. } 20. } What is the result? (A) A, B, C, (B) B, C, A, (C) Compilation fails. (D) The code runs with no output (E) An exception is thrown at runtime.