<tr>
<td class="tbgc" width="160"><a href="/developerWorks/cgi-bin/click.cgi?url=http://www.ibm.com/cn"><img height="47" width="160" alt="IBM" border="0" src="../i/ibm-logo.gif"></a></td><td class="tbg" width="195"><font color="#99ccff" size="2"><b>中國</b></font><a href="#main"><img alt="Skip to main content" height="1" width="195" border="0" src="../i/c.gif"></a></td><td valign="top" align="right" class="tbgc" width="100%">
<table cellspacing="0" cellpadding="0" border="0">
<form name="form1" id="form1" action="http://202.95.2.149/cgi-bin/dWsearch.pl" method="get">
<tr>
<td colspan="6"><img alt="" height="4" width="390" border="0" src="../i/c.gif"></td>
</tr>
<tr valign="middle">
<td class="dwsearch" height="8"><select class="dwsearch" name="selScope"><option value="dW">dW 中國所有內容</option><option value="dW">.................  </option><option value="dW">dW 中國技術專區:</option><option value="comptZ">　組件技術</option><option value="javaZ">　Java 技術</option><option value="linuxZ">　Linux</option><option value="xmlZ">　XML</option><option value="linuxZ">dW 中國特別專題:</option><option value="securityZ">　安全</option><option value="unicodeZ">　Unicode</option><option value="all">IBM 全部內容</option></select></td><td class="small"><img alt="" border="0" height="1" width="5" src="../i/c.gif"></td><td><input maxlength="100" size="15" height="15" name="UserRestriction" class="dwsearch" type="text"></td><td><img alt="" height="1" width="5" border="0" src="../i/c.gif"></td><td width="64"><input alt="搜索" name="Search" value="Search" border="0" height="23" width="64" src="../i/search.gif" type="image"></td><td valign="top"><img alt="" height="1" width="34" border="0" src="../i/c.gif"></td>
</tr>
<tr valign="top">
<td class="small" colspan="6"><a target="_blank" style="color: #ffffff;" href="http://202.95.2.149/help.htm">高級搜索</a><img alt="" height="1" width="1" border="0" src="../i/c.gif"></td>
</tr>
<tr>
<td colspan="6"><img alt="" height="4" width="390" border="0" src="../i/c.gif"></td>
</tr>
</form>
</table>
</td>
</tr>
<tr>
<td class="hbg" height="21" width="160"></td><td class="bbg" valign="top" height="21" colspan="2">　　<a href="/developerWorks/cgi-bin/click.cgi?url=http://www-900.ibm.com/cn/" class="mainlink">IBM 主頁</a><span class="divider">　| </span><a href="/developerWorks/cgi-bin/click.cgi?url=http://www-900.ibm.com/cn/products/index.shtml" class="mainlink">產品與服務</a><span class="divider">　|　</span><a href="/developerWorks/cgi-bin/click.cgi?url=http://www-900.ibm.com/cn/support/index.shtml" class="mainlink">支持與下載</a><span class="divider">　|　</span><a href="/developerWorks/cgi-bin/click.cgi?url=http://www-900.ibm.com/cn/account/index.shtml" class="mainlink">個性化服務</a></td>
</tr>
</table>
<TABLE width="100%" cellspacing="0" cellpadding="0" border="0">
<TR>
<TD bgcolor="#ffffff" height="1" width="150"><IMG src="../i/c.gif" width="150" height="1"></TD>
</TR>
<TR>
<TD bgcolor="#cc6633" height="3" width="150"><IMG src="../i/c.gif" width="150" height="3"></TD>
</TR>
<TR>
<TD bgcolor="#333333" height="1" width="150"><IMG src="../i/c.gif" width="150" height="1"></TD>
</TR>
<TR>
<TD bgcolor="#000000" height="1" width="150"><IMG src="../i/c.gif" width="150" height="1"></TD>
</TR>
<TR>
<TD bgcolor="#ffffff" height="1" width="150"><IMG src="../i/c.gif" width="150" height="2"></TD>
</TR>
</TABLE>
<table border="0" cellpadding="0" cellspacing="0" width="100%">
<tr>
<td><font size="-1" face="Verdana, sans-serif"><a href="http://www.ibm.com/">IBM</a> : <a href="/developerWorks/cn/index.shtml">developerWorks 中國網站</a> : <a href="/developerWorks/cn/java/index.shtml">java</a> ： <a href="/developerWorks/cn/cnedu.nsf/java-onlinecourse-bytitle?OpenView&Count=500">教學 - 在線教程</a></font>
<br>
<img alt=" Java 認證成功之路，第 1 部分：SCJP " src="imagemaster/masthead.jpg"></td><td width="*" valign="bottom" align="right"><a border="0" href="j-scjp.zip"><img alt="下載 ZIP 文件" border="0" src="../i/icon-zip.gif"></a><a target="_blank" href="../tutorial_eng/index.html" border="0"><img alt="英文原文" border="0" src="../i/icon-source.gif"></a>
					
					
					
&nbsp;&nbsp;&nbsp;
				</td>
</tr>
<tr>
<td height="2" colspan="2"><img height="2" width="1" src="../i/c.gif"></td>
</tr>
</table>
<TABLE border="0" cellpadding="0" cellspacing="0" width="100%">
<TR>
<TD width="150" height="1" bgcolor="#000000" colspan="6"><IMG alt="" height="1" width="150" src="../i/c.gif"></TD>
</TR>
<TR>
<TD background="../i/sw-gold.gif"><a border="0" href="index.html" onMouseOver="iOver('topmain'); iOver('bottommain'); self.status=mainblurb; return true;" onMouseOut="iOut('topmain'); iOut('bottommain'); self.status=''; return true;"><img alt="主菜單" border="0" src="../i/main.gif" name="topmain"></a></TD><TD background="../i/sw-gold.gif"><a border="0" onMouseOver="iOver('topsection'); iOver('bottomsection'); self.status=sectionblurb; return true;" onMouseOut="iOut('topsection'); iOut('bottomsection'); self.status=''; return true;" href="index9.html"><img alt="章節菜單" border="0" src="../i/section.gif" name="topsection"></a></TD><TD background="../i/sw-gold.gif"><a border="0" onMouseOver="iOver('topfeedback'); iOver('bottomfeedback'); self.status=feedbackblurb; return true;" onMouseOut="iOut('topfeedback'); iOut('bottomfeedback'); self.status=''; return true;" href="j-scjp-11-3.html"><img alt="給出此教程的反饋意見" border="0" src="../i/feedback.gif" name="topfeedback"></a></TD><TD width="100%" background="../i/sw-gold.gif"><img src="../i/c.gif"></TD><TD background="../i/sw-gold.gif"><a border="0" onMouseOver="iOver('topprevious'); iOver('bottomprevious'); self.status=previousblurb; return true;" onMouseOut="iOut('topprevious'); iOut('bottomprevious'); self.status=''; return true;" href="j-scjp-9-4.html"><img alt="上頁" border="0" src="../i/previous.gif" name="topprevious"></a></TD><TD background="../i/sw-gold.gif"><img border="0" src="../i/xnext.gif"></TD>
</TR>
<TR>
<TD width="100%" colspan="5"></TD><TD width="108" height="1" bgcolor="#000000" align="right"><IMG alt="" height="1" width="108" src="../i/c.gif"></TD>
</TR>
<TR>
<TD colspan="5"></TD><TD align="right"><a border="0" onMouseOver="iOver('topnextsection'); iOver('bottomnextsection'); self.status=nextsectionblurb; return true;" onMouseOut="iOut('topnextsection'); iOut('bottomnextsection'); self.status=''; return true;" href="j-scjp-10-1.html"><img alt="下一章" src="../i/nextsection.gif" border="0" name="topnextsection"></a></TD>
</TR>
</TABLE>
<table bgcolor="ffffff" cellspacing="0" cellpadding="2" border="0" height="400" width="100%">
<tr valign="bottom">
<a name="navskip"></a><td height="25" colspan="4"><img alt="9.java.lang 包中的基本類 " src="imagemaster/titlebar9.jpg" border="0" height="25" width="562"></td>
</tr>
<tr>
<td bgcolor="ffffff" width="15">&nbsp;</td><td bgcolor="ffffff" width="12">&nbsp;</td><td valign="top" align="left" bgcolor="ffffff" width="*">
<p>
<br>
<table cellspacing="0" cellpadding="0" border="0">
<tr>
<td width="90%"><font size="4" face="Verdana, Arial, Helvetica"><b>練習 </b></font></td><td width="200" align="right"><font size="1" face="Verdana, Arial, Helvetica"><nobr>   第 5 頁（共5 頁）</nobr></font></td>
</tr>
</table>
<br>
<br>
</p>
<font size="2" face="Verdana, Arial, Helvetica">
<p>
						
<b>問題： </b>
					
</p>
<p>編譯和運行以下程序會有什么結果？ </p>
<pre>
<code style="font-family: Courier New, Courier, monospace; font-size: 12">
  class Test 
  {
    public static void main(String args[])	
    {
      String s1 = "abc";
      String s2 = "abc";
      s1 += "xyz";
      s2.concat("pqr");
      s1.toUpperCase();
      System.out.println(s1 + s2);
    }
  }
</code>
</pre>
<p>
						
<b>選項： </b>
					
</p>
<ul>
<li>A.	"abcxyzabc"</li>
<li>B.	"abcxyzabcpqr"</li>
<li>C.	"ABCXYZabcpqr"</li>
<li>D.	"ABCXYZabc"</li>
<li>E.	代碼不能編譯  </li>
</ul>
<p>
						
<b>正確答案： </b>
					
</p>
<ul>
<li>A</li>
</ul>
<p>
						
<b>說明： </b>
					
</p>
<p>這段代碼可以無錯誤地編譯運行，輸出&ldquo;abcxyxabc&rdquo;。在這段代碼中， <code>s1</code> 和 <code>s2</code> 最初指向同一個 <code>String</code> 對象&ldquo;abc&rdquo;。當&ldquo;xyz&rdquo;連接到 <code>s1</code> 上時，就創建了一個新的 <code>String</code> 對象&ldquo;abcxyz&rdquo; ，并且 <code>s1</code> 指向它。注意 <code>s2</code> 仍然指向原來的 <code>String</code> 對象&ldquo;abc&rdquo;，它沒有改變。 <code>concat()</code> 和 <code>toUpperCase()</code> 方法沒有任何效果，因為作為這些操作的結果創建的新 <code>String</code> 對象不擁有任何引用。所以最后 <code>s1</code> 包含&ldquo;abcxyz&rdquo;而 <code>s2</code> 包含&ldquo;abc&rdquo;，從而 A 為正確結果。 </p>
<br>
</font></td>
</tr>
</table>
<TABLE border="0" cellpadding="0" cellspacing="0" width="100%">
<TR>
<TD align="right" colspan="6"><a border="0" onMouseOver="iOver('topnextsection'); iOver('bottomnextsection'); self.status=nextsectionblurb; return true;" onMouseOut="iOut('topnextsection'); iOut('bottomnextsection'); self.status=''; return true;" href="j-scjp-10-1.html"><img alt="下一章" src="../i/nextsection.gif" border="0" name="bottomnextsection"></a></TD>
</TR>
<TR>
<TD width="100%" colspan="5"></TD><TD width="108" height="1" bgcolor="#000000" align="right"><IMG alt="" height="1" width="108" src="../i/c.gif"></TD>
</TR>
<TR>
<TD background="../i/sw-gold.gif"><a border="0" href="index.html" onMouseOver="iOver('topmain'); iOver('bottommain'); self.status=mainblurb; return true;" onMouseOut="iOut('topmain'); iOut('bottommain'); self.status=''; return true;"><img alt="主菜單" border="0" src="../i/main.gif" name="bottommain"></a></TD><TD background="../i/sw-gold.gif"><a border="0" onMouseOver="iOver('topsection'); iOver('bottomsection'); self.status=sectionblurb; return true;" onMouseOut="iOut('topsection'); iOut('bottomsection'); self.status=''; return true;" href="index9.html"><img alt="章節菜單" border="0" src="../i/section.gif" name="bottomsection"></a></TD><TD background="../i/sw-gold.gif"><a border="0" onMouseOver="iOver('topfeedback'); iOver('bottomfeedback'); self.status=feedbackblurb; return true;" onMouseOut="iOut('topfeedback'); iOut('bottomfeedback'); self.status=''; return true;" href="j-scjp-11-3.html"><img alt="給出此教程的反饋意見" border="0" src="../i/feedback.gif" name="bottomfeedback"></a></TD><TD width="100%" background="../i/sw-gold.gif"><img src="../i/c.gif"></TD><TD background="../i/sw-gold.gif"><a border="0" onMouseOver="iOver('topprevious'); iOver('bottomprevious'); self.status=previousblurb; return true;" onMouseOut="iOut('topprevious'); iOut('bottomprevious'); self.status=''; return true;" href="j-scjp-9-4.html"><img alt="上頁" border="0" src="../i/previous.gif" name="bottomprevious"></a></TD><TD background="../i/sw-gold.gif"><img border="0" src="../i/xnext.gif"></TD>
</TR>
<TR>
<TD width="150" height="1" bgcolor="#000000" colspan="6"><IMG alt="" height="1" width="150" src="../i/c.gif"></TD>
</TR>
</TABLE>
<TABLE width="100%" cellpadding="0" cellspacing="0" border="0">
<TR>
<TD width="100%">
<table border="0" cellpadding="0" cellspacing="0" width="100%">
<tr>
<td><img alt="" height="1" width="1" src="../i/c.gif"></td>
</tr>
<tr valign="top">
<td class="bbg" height="21">　<a class="mainlink" href="/developerWorks/cgi-bin/click.cgi?url=http://www-900.ibm.com/cn/ibm/index.shtml">關于 IBM</a><span class="divider">　| </span><a class="mainlink" href="/developerWorks/cgi-bin/click.cgi?url=http://www-900.ibm.com/cn/ibm/privacy/index.shtml">隱私條約</a><span class="divider">　| </span><a class="mainlink" href="/developerWorks/cgi-bin/click.cgi?url=http://www-900.ibm.com/cn/ibm/legal/index.shtml">法律條款</a><span class="divider">　| </span><a class="mainlink" href="/developerWorks/cgi-bin/click.cgi?url=http://www-900.ibm.com/cn/ibm/contact/index.shtml">聯系 IBM</a></td>
</tr>
</table>
</TD>
</TR>
</TABLE>
<script src="//www.ibm.com/common/stats/stats.js" language="JavaScript1.2" type="text/javascript"></script>
<noscript>
<img border="0" alt="" height="1" width="1" src="//stats.www.ibm.com/rc/images/uc.GIF?R=noscript"></noscript>
</body>
</html>