第196題

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);
答案：B
參考：12-4-3 SortedSet集合、12-5-1 HashMap
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C. Collections.sort(s); //s要為list才可以,不能用set