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12. Collections and Generics

Q: 34
A programmer must create a generic class MinMax and the type parameter
of MinMax must implement Comparable. Which implementation of MinMax will compile?
A. class MinMax<E extends Comparable<E>> {
E min = null;
E max = null;
public MinMax() {}
public void put(E value) { /* store min or max */ }
B. class MinMax<E implements Comparable<E>> {
E min = null;
E max = null;
public MinMax() {}
public void put(E value) { /* store min or max */ }
C. class MinMax<E extends Comparable<E>> {
<E> E min = null;
<E> E max = null;
public MinMax() {}
public <E> void put(E value) { /* store min or max */ }
D. class MinMax<E implements Comparable<E>> {
<E> E min = null;
<E> E max = null;
public MinMax() {}
public <E> void put(E value) { /* store min or max */ }
Answer: A

Q: 35 Given:
int[] myArray = new int[] {1, 2, 3, 4, 5}; What allows you to create a list from this array?
A. List myList = myArray.asList();
B. List myList = Arrays.asList(myArray);
C. List myList = new ArrayList(myArray);
D. List myList = Collections.fromArray(myArray);
Answer: B

Question: 36
Given:
1. public class Score implements Comparable<Score> {
2. private int wins, losses;
3. public Score(int w, int 1) { wins = w; losses = 1; }
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) {/*mode 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*/}
Answer: B

Question: 37
Click the Exhibit button.
1. import java.util.*;
2. class KeyMaster {
3. public int i;
4. public KeyMaster(int i) { this.i = i; }
5. public boolean equals(Object o) { return i == ((KeyMaster)o).i; }
6. public int hashCode() { return i; }
7. }
8. public class MapIt {
9. public static void main(String[] args) {
10. Set<KeyMaster> set = new HashSet<KeyMaster>();
11. KeyMaster k1 = new KeyMaster(1);
12. KeyMaster k2 = new KeyMaster(2);
13. set.add(k1); set.add(k1);
14. set.add(k2); set.add(k2);
15. System.out.print(set.size() + “:”);
16. k2.i = 1;
17. System.out.print(set.size() + “:”);
18. set.remove(k1);
19. System.out.print(set.size() + “:”);
20. set.remove(k2);
21. System.out.print(set.size());
22. }
23. }
What is the result?
A. 4:4:2:2                             B. 4:4:3:2
C. 2:2:1:0                             D. 2:2:0:0
E. 2:1:0:0                              F. 2:2:1:1
G. 4:3:2:1
Answer: F

Question: 38
Given:
1. import java.util.*;
2. public class Test {
3. public static void main(String[] args) {
4. List<String> strings = new ArrayList<String>();
5. // insert code here
6. }
7. }
Which four, inserted at line 5, will allow compilation to succeed?
(Choose four.)
A. String s = strings.get(0);
B. Iterator i1 = strings.iterator();
C. String[] array1 = strings.toArray();
D. Iterator<String> i2 = strings.iterator();
E. String[] array2 = strings.toArray(new String[1]);
F. Iterator<String> i3 = strings.iterator<String>();
Answer: ABDE

Question: 39
Given:
classA {}
class B extends A {}
class C extends A {}
class D extends B {}
Which three statements are true? (Choose three.)
A. The type List<A> is assignable to List.
B. The type List<B> is assignable to List<A>.
C. The type List<Object> is assignable to List<?>.
D. The type List<D> is assignable to List<? extends B>.
E. The type List<? extends A> is assignable to List<A>.
F. The type List<Object> is assignable to any List reference.
G. The type List<? extends B> is assignable to List<? extends A>.

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