??xml version="1.0" encoding="utf-8" standalone="yes"?>国产不卡高清在线观看视频,亚洲第一精品久久忘忧草社区,精品国产成人avhttp://www.aygfsteel.com/zoubin/奋进zh-cnTue, 17 Jun 2025 04:09:40 GMTTue, 17 Jun 2025 04:09:40 GMT60JAVA的可变类与不可变c?/title><link>http://www.aygfsteel.com/zoubin/archive/2014/09/23/418207.html</link><dc:creator>zoubin</dc:creator><author>zoubin</author><pubDate>Tue, 23 Sep 2014 15:46:00 GMT</pubDate><guid>http://www.aygfsteel.com/zoubin/archive/2014/09/23/418207.html</guid><wfw:comment>http://www.aygfsteel.com/zoubin/comments/418207.html</wfw:comment><comments>http://www.aygfsteel.com/zoubin/archive/2014/09/23/418207.html#Feedback</comments><slash:comments>0</slash:comments><wfw:commentRss>http://www.aygfsteel.com/zoubin/comments/commentRss/418207.html</wfw:commentRss><trackback:ping>http://www.aygfsteel.com/zoubin/services/trackbacks/418207.html</trackback:ping><description><![CDATA[<ol style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;"><li>可变cd不可变类(Mutable and Immutable Objects)的初步定义:<br />可变c:当你获得q个cȝ一个实例引用时Q你可以改变q个实例的内宏V?br />不可变类Q当你获得这个类的一个实例引用时Q你不可以改变这个实例的内容。不可变cȝ实例一但创建,其内在成员变量的值就不能被修攏V?/li><li>如何创徏一个自q不可变类Q?br />.所有成员都是private<br />.不提供对成员的改变方法,例如QsetXXXX<br />.保所有的Ҏ不会被重载。手D|两种Q用final Class(Z可变c?Q或者将所有类Ҏ加上final(׃可变c??br />.如果某一个类成员不是原始变量(primitive)或者不可变c,必须通过在成员初始化(in)或者getҎ(out)旉过深度cloneҎQ来保cȝ不可变?/li><li>一个示?/li></ol><p style="margin: 0px 0px 14px; font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;"> import java.util.Date;                                           <br /> public final class BrokenPerson                                 <br /> {                                                               <br />  private String firstName;                                     <br />  private String lastName;                                      <br />  private Date dob;                                             <br />                                          <br />  public BrokenPerson( String firstName,                   public BetterPerson( String firstName, <br />    String lastName, Date dob)                                             String lastName, Date dob)           <br />  {                                                                                      {                                      <br />   this.firstName = firstName;                                             this.firstName = firstName;          <br />   this.lastName = lastName;                                             this.lastName = lastName;            <br />   <strong>this.dob = dob;     //error              </strong><strong> this.dob = new Date( dob.getTime() ); //correct<br /></strong>  }                                                                                       }                                      <br />                                                             <br />  public String getFirstName()<br />  {<br />   return this.firstName;<br />  }<br />  public String getLastName()<br />  {<br />   return this.lastName;<br />  }<br />  public Date getDOB()                                               public Date getDOB()                      <br />  {                                                                                    {                                       <br />  <strong> return this.dob;    //error                  return new Date( this.dob.getTime() );//correct<br /></strong>  }                                                                                     }                                       <br /> }<br />  4. jdk的可变类和不可变c?/p><p style="margin: 0px 0px 14px; font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;">primitive变量: boolean,byte, char, double ,float, integer, long, short <br />jdk的不可变c:jdk的java.lang包中 Boolean, Byte, Character, Double, Float, Integer, Long, Short, String. <br />  <br />  StringBuffer 可变c?br />  java.util.Date 可变c?br /><br /></p><hr style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><p style="margin: 0px 0px 14px; font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;"></p><span style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;">对于q个pd里的问题Q每个学Java的h都应该搞懂。当Ӟ如果只是学Java玩玩无所谓了。如果你认ؓ自己已经越初学者了Q却不很懂这些问题,请将你自己重归初学者行列。内容均来自于CSDN的经典老脓?/span><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><strong style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;">问题一Q?/strong><span style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px; color: red;">我声明了什么!</span><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><span style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;">String s = "Hello world!";</span><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><span style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;">许多人都做过q样的事情,但是Q我们到底声明了什么?回答通常是:一个StringQ内Ҏ“Hello world!”。这hp的回答通常是概念不清的Ҏ。如果要准确的回{,一半的人大概会回答错误?/span><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><span style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;">q个语句声明的是一个指向对象的引用Q名?#8220;s”Q可以指向类型ؓString的Q何对象,目前指向"Hello world!"q个Stringcd的对象。这是真正发生的事情。我们ƈ没有声明一个String对象Q我们只是声明了一个只能指向String对象的引用变量。所以,如果在刚才那句语句后面,如果再运行一句:</span><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><span style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;">String string = s;</span><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><span style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;">我们是声明了另外一个只能指向String对象的引用,名ؓstringQƈ没有W二个对象生,stringq是指向原来那个对象Q也是Q和s指向同一个对象?/span><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><strong style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;">问题二:</strong><span style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px; color: red;">"=="和equalsҎI竟有什么区别?</span><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><span style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;">==操作W专门用来比较变量的值是否相{。比较好理解的一ҎQ?/span><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><span style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;">int a=10;</span><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><span style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;">int b=10;</span><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><span style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;">则a==b是true?/span><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><span style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;">但不好理解的地方是:</span><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><span style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;">String a=new String("foo");</span><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><span style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;">String b=new String("foo");</span><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><span style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;">则a==b返回false?/span><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><span style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;">Ҏ前一帖说q,对象变量其实是一个引用,它们的值是指向对象所在的内存地址Q而不是对象本w。a和b都用了new操作W,意味着在内存中生两个内容ؓ"foo"的字W串Q既然是“两个”Q它们自然位于不同的内存地址。a和b的值其实是两个不同的内存地址的|所以?=="操作W,l果会是false。诚Ӟa和b所指的对象Q它们的内容都是"foo"Q应该是“相等”Q但?=操作Wƈ不涉及到对象内容的比较?/span><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><span style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;">对象内容的比较,正是equalsҎ做的事?/span><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><span style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;">看一下Object对象的equalsҎ是如何实现的Q?/span><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><span style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;">boolean equals(Object o){</span><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><span style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;">return this==o;</span><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><span style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;">}</span><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><span style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;">Object对象默认使用?=操作W。所以如果你自创的类没有覆盖equalsҎQ那你的cM用equals和?=会得到同Ll果。同样也可以看出QObject的equalsҎ没有辑ֈequalsҎ应该辑ֈ的目标:比较两个对象内容是否相等。因为答案应该由cȝ创徏者决定,所以Object把这个Q务留l了cȝ创徏者?/span><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><span style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;">看一下一个极端的c:</span><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><span style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;">Class Monster{</span><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><span style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;">private String content;</span><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><span style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;">...</span><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><span style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;">boolean equals(Object another){ return true;}</span><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><span style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;">}</span><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><span style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;">我覆盖了equalsҎ。这个实CD无论Monster实例内容如何Q它们之间的比较永远q回true?/span><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><span style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;">所以当你是用equalsҎ判断对象的内Ҏ否相{,请不要想当然。因为可能你认ؓ相等Q而这个类的作者不q样认ؓQ而类的equalsҎ的实现是׃掌握的。如果你需要用equalsҎQ或者用Q何基于散列码的集合(HashSet,HashMap,HashTableQ,请察看一下java doc以确认这个类的equals逻辑是如何实现的?/span><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><strong style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;">问题三:</strong><span style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px; color: red;">String到底变了没有Q?/span><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><span style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;">没有。因为String被设计成不可?immutable)c,所以它的所有对象都是不可变对象。请看下列代码:</span><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><span style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;">String s = "Hello";</span><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><span style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;">s = s + " world!";</span><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><span style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;">s所指向的对象是否改变了呢?从本pdW一的l论很容易导个结论。我们来看看发生了什么事情。在q段代码中,s原先指向一个String对象Q内Ҏ"Hello"Q然后我们对sq行?操作Q那么s所指向的那个对象是否发生了改变呢?{案是没有。这Ӟs不指向原来那个对象了Q而指向了另一个String对象Q内容ؓ"Hello world!"Q原来那个对象还存在于内存之中,只是sq个引用变量不再指向它了?/span><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><span style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;">通过上面的说明,我们很容易导出另一个结论,如果l常对字W串q行各种各样的修改,或者说Q不可预见的修改Q那么用String来代表字W串的话会引起很大的内存开销。因为String对象建立之后不能再改变,所以对于每一个不同的字符Ԍ都需要一个String对象来表C。这Ӟ应该考虑使用StringBufferc,它允怿改,而不是每个不同的字符串都要生成一个新的对象。ƈ且,q两U类的对象{换十分容易?/span><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><span style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;">同时Q我们还可以知道Q如果要使用内容相同的字W串Q不必每ơ都new一个String。例如我们要在构造器中对一个名叫s的String引用变量q行初始化,把它讄为初始|应当q样做:</span><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><span style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;">public class Demo {</span><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><span style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;">  private String s;</span><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><span style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;">  ...</span><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><span style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;">  public Demo {</span><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><span style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;">    s = "Initial Value";</span><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><span style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;">  }</span><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><span style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;">  ...</span><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><span style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;">}</span><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><span style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;">而非</span><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><span style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;">s = new String("Initial Value");</span><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><span style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;">后者每ơ都会调用构造器Q生成新对象Q性能低下且内存开销大,q且没有意义Q因为String对象不可改变Q所以对于内容相同的字符Ԍ只要一个String对象来表C就可以了。也pQ多ơ调用上面的构造器创徏多个对象Q他们的Stringcd属性s都指向同一个对象?/span><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><span style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;">上面的结Zq样一个事实:对于字符串常量,如果内容相同QJava认ؓ它们代表同一个String对象。而用关键字new调用构造器QL会创Z个新的对象,无论内容是否相同?/span><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><span style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;">至于Z么要把Stringc设计成不可变类Q是它的用途决定的。其实不只StringQ很多Java标准cd中的c都是不可变的。在开发一个系l的时候,我们有时候也需要设计不可变c,来传递一l相关的|q也是面向对象思想的体现。不可变cL一些优点,比如因ؓ它的对象是只ȝQ所以多U程q发讉K也不会有M问题。当然也有一些缺点,比如每个不同的状态都要一个对象来代表Q可能会造成性能上的问题。所以Java标准cdq提供了一个可变版本,即StringBuffer?/span><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><strong style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;">问题四:</strong><span style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px; color: red;">final关键字到底修C什么?</span><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><span style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;">final使得被修饰的变量"不变"Q但是由于对象型变量的本质是“引用”Q?#8220;不变”也有了两U含义:引用本n的不变,和引用指向的对象不变?/span><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><span style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;">引用本n的不变:</span><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><span style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;">final StringBuffer a=new StringBuffer("immutable");</span><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><span style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;">final StringBuffer b=new StringBuffer("not immutable");</span><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><span style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;">a=b;//~译期错?/span><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><span style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;">引用指向的对象不变:</span><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><span style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;">final StringBuffer a=new StringBuffer("immutable");</span><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><span style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;">a.append(" broken!"); //~译通过</span><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><span style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;">可见Qfinal只对引用?#8220;?#8221;(也即它所指向的那个对象的内存地址)有效Q它q引用只能指向初始指向的那个对象,改变它的指向会导致编译期错误。至于它所指向的对象的变化Qfinal是不负责的。这很类?=操作W:==操作W只负责引用?#8220;?#8221;相等Q至于这个地址所指向的对象内Ҏ否相{,==操作W是不管的?/span><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><span style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;">理解final问题有很重要的含义。许多程序漏z都Z?---final只能保证引用永远指向固定对象Q不能保证那个对象的状态不变。在多线E的操作?一个对象会被多个线E共享或修改Q一个线E对对象无意识的修改可能会导致另一个用此对象的线E崩溃。一个错误的解决Ҏ是在此对象新徏的时候把它声明ؓfinalQ意图得它“永远不变”。其实那是徒劳的?/span><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><strong style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;">问题五:</strong><span style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px; color: red;">到底要怎么样初始化Q?/span><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><span style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;">本问题讨论变量的初始化,所以先来看一下Java中有哪些U类的变量?/span><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><span style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;">1. cȝ属性,或者叫值域</span><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><span style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;">2. Ҏ里的局部变?/span><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><span style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;">3. Ҏ的参?/span><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><span style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;">对于W一U变量,Java虚拟Z自动q行初始化。如果给Z初始|则初始化初始倹{如果没有给出,则把它初始化cd变量的默认初始倹{?/span><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><span style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;">intcd变量默认初始gؓ0</span><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><span style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;">floatcd变量默认初始gؓ0.0f</span><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><span style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;">doublecd变量默认初始gؓ0.0</span><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><span style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;">booleancd变量默认初始gؓfalse</span><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><span style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;">charcd变量默认初始gؓ0(ASCII?</span><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><span style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;">longcd变量默认初始gؓ0</span><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><span style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;">所有对象引用类型变量默认初始gؓnullQ即不指向Q何对象。注意数l本w也是对象,所以没有初始化的数l引用在自动初始化后其g是null?/span><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><span style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;">对于两种不同的类属性,static属性与instance属性,初始化的时机是不同的。instance属性在创徏实例的时候初始化Qstatic属性在cd载,也就是第一ơ用到这个类的时候初始化Q对于后来的实例的创建,不再ơ进行初始化。这个问题会在以后的pd中进行详l讨论?/span><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><span style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;">对于W二U变量,必须明确地进行初始化。如果再没有初始化之前就试图使用它,~译器会抗议。如果初始化的语句在try块中或if块中Q也必须要让它在W一ơ用前一定能够得到赋倹{也是_把初始化语句攑֜只有if块的条g判断语句中编译器也会抗议Q因为执行的时候可能不W合if后面的判断条Ӟ如此一来初始化语句׃会被执行了,q就q反了局部变量用前必须初始化的规定。但如果在else块中也有初始化语句,可以通过~译Q因为无论如何,L臛_一条初始化语句会被执行Q不会发生用前未被初始化的事情。对于try-catch也是一P如果只有在try块里才有初始化语句,~译部通过。如果在catch或finally里也有,则可以通过~译。MQ要保证局部变量在使用之前一定被初始化了。所以,一个好的做法是在声明他们的时候就初始化他们,如果不知道要Z化成什么值好Q就用上面的默认值吧Q?/span><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><span style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;">其实W三U变量和W二U本质上是一LQ都是方法中的局部变量。只不过作ؓ参数Q肯定是被初始化q的Q传入的值就是初始|所以不需要初始化?/span><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><strong style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;">问题六:</strong><span style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px; color: red;">instanceof是什么东东?</span><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><span style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;">instanceof是Java的一个二元操作符Q和==Q?gt;Q?lt;是同一cM东。由于它是由字母l成的,所以也是Java的保留关键字。它的作用是试它左边的对象是否是它双的类的实例,q回booleancd的数据。D个例子:</span><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><span style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;">String s = "I AM an Object!";</span><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><span style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;">boolean isObject = s instanceof Object;</span><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><span style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;">我们声明了一个String对象引用Q指向一个String对象Q然后用instancof来测试它所指向的对象是否是Objectcȝ一个实例,昄Q这是真的,所以返回trueQ也是isObject的gؓTrue?/span><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><span style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;">instanceof有一些用处。比如我们写了一个处理̎单的pȝQ其中有q样三个c:</span><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><span style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;">public class Bill {//省略l节}</span><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><span style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;">public class PhoneBill extends Bill {//省略l节}</span><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><span style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;">public class GasBill extends Bill {//省略l节}</span><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><span style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;">在处理程序里有一个方法,接受一个Billcd的对象,计算金额。假设两U̎单计方法不同,而传入的Bill对象可能是两U中的Q何一U,所以要用instanceof来判断:</span><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><span style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;">public double calculate(Bill bill) {</span><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><span style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;">  if (bill instanceof PhoneBill) {</span><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><span style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;">    //计算电话账单</span><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><span style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;">  }</span><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><span style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;">  if (bill instanceof GasBill) {</span><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><span style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;">    //计算燃气账单</span><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><span style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;">  }</span><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><span style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;">  ...</span><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><span style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;">}</span><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><span style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;">q样可以用一个方法处理两U子cR?/span><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><span style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;">然而,q种做法通常被认为是没有好好利用面向对象中的多态性。其实上面的功能要求用方法重载完全可以实玎ͼq是面向对象变成应有的做法,避免回到l构化编E模式。只要提供两个名字和q回值都相同Q接受参数类型不同的Ҏ可以了Q?/span><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><span style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;">public double calculate(PhoneBill bill) {</span><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><span style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;">  //计算电话账单</span><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><span style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;">}</span><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><span style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;">public double calculate(GasBill bill) {</span><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><span style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;">  //计算燃气账单</span><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><span style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;">}</span><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><br style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;" /><span style="font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 19.2000007629395px;">所以,使用instanceof在绝大多数情况下q不是推荐的做法Q应当好好利用多?/span><img src ="http://www.aygfsteel.com/zoubin/aggbug/418207.html" width = "1" height = "1" /><br><br><div align=right><a style="text-decoration:none;" href="http://www.aygfsteel.com/zoubin/" target="_blank">zoubin</a> 2014-09-23 23:46 <a href="http://www.aygfsteel.com/zoubin/archive/2014/09/23/418207.html#Feedback" target="_blank" style="text-decoration:none;">发表评论</a></div>]]></description></item></channel></rss> <footer> <div class="friendship-link"> <a href="http://www.aygfsteel.com/" title="狠狠久久亚洲欧美专区_中文字幕亚洲综合久久202_国产精品亚洲第五区在线_日本免费网站视频">狠狠久久亚洲欧美专区_中文字幕亚洲综合久久202_国产精品亚洲第五区在线_日本免费网站视频</a> </div> </footer> վ֩ģ壺 <a href="http://" target="_blank">ͷ</a>| <a href="http://" target="_blank"></a>| <a href="http://" target="_blank"></a>| <a href="http://" target="_blank">ũ</a>| <a href="http://" target="_blank"></a>| <a href="http://" target="_blank">ű</a>| <a href="http://" target="_blank"></a>| <a href="http://" target="_blank">ɽ</a>| <a href="http://" target="_blank"></a>| <a href="http://" target="_blank">IJ</a>| <a href="http://" target="_blank">Ƹ</a>| <a href="http://" target="_blank"></a>| <a href="http://" target="_blank">ǿ</a>| <a href="http://" target="_blank">ɽ</a>| <a href="http://" target="_blank"></a>| <a href="http://" target="_blank"></a>| <a href="http://" target="_blank"></a>| <a href="http://" target="_blank"></a>| <a href="http://" target="_blank"></a>| <a href="http://" target="_blank"></a>| <a href="http://" target="_blank"></a>| <a href="http://" target="_blank">IJ</a>| <a href="http://" target="_blank">ƽ</a>| <a href="http://" target="_blank"></a>| <a href="http://" target="_blank"></a>| <a href="http://" target="_blank"></a>| <a href="http://" target="_blank">鶴</a>| <a href="http://" target="_blank"></a>| <a href="http://" target="_blank"></a>| <a href="http://" target="_blank">ƽ</a>| <a href="http://" target="_blank"></a>| <a href="http://" target="_blank">־</a>| <a href="http://" target="_blank"></a>| <a href="http://" target="_blank"></a>| <a href="http://" target="_blank">ͬ</a>| <a href="http://" target="_blank">ʡ</a>| <a href="http://" target="_blank">Ȫ</a>| <a href="http://" target="_blank">¦</a>| <a href="http://" target="_blank"></a>| <a href="http://" target="_blank">ͨ</a>| <a href="http://" target="_blank"></a>| <script> (function(){ var bp = document.createElement('script'); 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