SCJP 1.6版考題 191

Given:
11. //insert code here
12. private N min, max;
13. public N getMin() { return min; }
14. public N getMax() { return max; }
15. public void add(N added) {
16.    if(min == null || added.doubleValue() < min.doubleValue())
17.    min = added;
18.    if(max == null || added.doubleValue() > max.doubleValue())
19.    max = added;
20.  }
21.}

Which two, inserted at line 11, will allow the code to compile? (Choose two.)
 A. public class MinMax<?>{
 B. public class MinMax<? extends Number>{
 C. public class MinMax<N extends Object>{
 D. public class MinMax<N extends Number>{
 E. public class MinMax<? extends Object>{
 F. public class MinMax<N extends Integer>{

解答

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Ans: D F

解說: Number 是Integer, Short等包裝型別的父類別