第190題

Given:
1. import java.util.*;
2. public class WrappedString{
3. private String s;
4. public WrappedString(String s){this.s = s;}
5. public static void main(String[] args){
6. HashSet(object) hs = new HashSet(object)();
7. WrappedString ws1 = new WrappedString("aardvark");
8. WrappedString ws2 = new WrappedString("aardvark");
9. String s1 = new String("aardvark");
10. String s2 = new String("aardvark");
11. hs.add(ws1); hs.add(ws2); hs.add(s1); hs.add(s2);
12. System.out.println(hs.size()); }}

What is the result?

A. 0
B. 1
C. 2
D. 3
E. 4
F. Compilation fails.
G. An exception is thrown at runtime.
答案：D

參考：12-4-2 equals()、hashCode()方法的改寫