Ikk：新頁面: 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){ ...

2013-03-30T00:24:59Z

新頁面: 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){ ...

新頁面

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.

<div class="toccolours mw-collapsible mw-collapsed">
<span style="font-size:medium;">解答</span>

----
<div class="mw-collapsible-content">
<span style="font-size: medium;">Ans: D </span>

<span style="font-size:medium;"> 解說:
hs物件有3個
ws1、ws2與s1(s2)
s1與s2為String，比較時一樣，所以不會重複加入hs
ws1與ws2因WrappedString類別並未定義hashCode與equals方法，無法比較 (會先比較hashCode()方法傳回的值是否相同，
如果相同，則再使用 equals()方法比較，如果兩者都相同，則視為相同的物件。)
</span>
</div></div>
{{SCJP 1.6版考題講解}}

SCJP 1.6版考題 190 - 修訂歷史

Ikk：新頁面: 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){ ...