Hi Here is another question from K&B:
8. Given:
12. public class AccountManager {
13. private Map accountTotals = new HashMap();
14. private int retirementFund;
15.
16. public int getBalance(
String accountName) {
17. Integer total = (Integer) accountTotals.get(accountName);
18. if (total == null)
19. total = Integer.valueOf(0);
20. return total.intValue();
21. }
23. public void setBalance(String accountName, int amount) {
24. accountTotals.put(accountName, Integer.valueOf(amount));
25. } }
This class is to be updated to make use of appropriate generic types, with no changes in
behavior (for better or worse). Which of these steps could be performed? (Choose three.)
A. Replace line 13 with
private Map<String, int> accountTotals = new HashMap<String, int>();
B. Replace line 13 with
private Map<String, Integer> accountTotals = new HashMap<String, Integer>();
C. Replace line 13 with
private Map<String<Integer>> accountTotals = new HashMap<String<Integer>>();
D. Replace lines 17�20 with
int total = accountTotals.get(accountName);
if (total == null) total = 0;
return total;
E. Replace lines 17�20 with
Integer total = accountTotals.get(accountName);
if (total == null) total = 0;
return total;
F. Replace lines 17�20 with
return accountTotals.get(accountName);
G. Replace line 24 with
accountTotals.put(accountName, amount);
The correct answers are B,E and G.
If E is correct, what's wrong with F? Cant the return value of accountTotals be unboxed on the fly?
The answer explaination says: "F is wrong because a null can't unbox to 0"
Can someone please decode this for me? What's null in here and where is do we have 0?
regards,
SCJPAspirant
