第195題

Given:

3. import java.util.*;
4. public class Mapit{
5. public static void main(String[] args){
6. Set set = new HashSet();
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.
F. An exception is thrown at runtime.
答案：B
參考：12-4-1 Set集合
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6. Set set = new HashSet();
9. set.add(i1);
10. set.add(i1);//不會放入,所以set到此只有一個元素
11. set.add(i2); System.out.print(set.size() + " "); //會放入所以有二元素
12. set.remove(i1); System.out.print(set.size() + " "); //移除一個元素所以剩一個元素
13. i2 = 47; //指的是i2 =new Integer(47);但set中的元素還是46
14. set.remove(i2); //set中沒有47這一個元素可以移除