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	<title>西格玛向量™ &#187; Java</title>
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	<description>指向 任何方向都是未来</description>
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		<title>Java学习笔记（一）</title>
		<link>http://sigmav.net/2009/10/06/java%e5%ad%a6%e4%b9%a0%e7%ac%94%e8%ae%b0%ef%bc%88%e4%b8%80%ef%bc%89/?utm_source=rss&#038;utm_medium=rss&#038;utm_campaign=java%25e5%25ad%25a6%25e4%25b9%25a0%25e7%25ac%2594%25e8%25ae%25b0%25ef%25bc%2588%25e4%25b8%2580%25ef%25bc%2589</link>
		<comments>http://sigmav.net/2009/10/06/java%e5%ad%a6%e4%b9%a0%e7%ac%94%e8%ae%b0%ef%bc%88%e4%b8%80%ef%bc%89/#comments</comments>
		<pubDate>Wed, 07 Oct 2009 00:38:53 +0000</pubDate>
		<dc:creator>西玛哒</dc:creator>
				<category><![CDATA[IT悟语]]></category>
		<category><![CDATA[Java]]></category>

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		<description><![CDATA[#前记：<br />&#160; java是一种面向对象的，相对比较低效的（这个不是定义！），通过基于字节码的中间代码和虚拟机（Java Virtual Machine，JVM，包含于 Java Runtime Environment(JRE)中）实现跨平台运行的，自称为安全的（死也不承认自己有指针）的网络化编程语言。<br />&#160;&#160;
java编程语言不像是C和C++，而它与ms的C#是久居异地的克隆兄弟关系，都有着傻瓜化的操作方式和一套自己的运行平台（.net FX 和
J...]]></description>
			<content:encoded><![CDATA[<p><span style="font-size: medium;"><strong>#前记：</strong></span><br />
java是一种面向对象的，相对比较低效的（这个不是定义！），通过基于字节码的中间代码和虚拟机（Java Virtual Machine，JVM，包含于 <strong>Java Runtime Environment</strong>(JRE)中）实现跨平台运行的，自称为安全的（死也不承认自己有指针）的网络化编程语言。</p>
<p>java编程语言不像是C和C++，而它与ms的C#是久居异地的克隆兄弟关系，都有着傻瓜化的操作方式和一套自己的运行平台（.net FX 和<br />
JVM），java适合J2EE大项目的开发，网站开发等，而对于要求效率的程序来说就不要想了。当然，java也不是不可以变得高效，但是，一个简单的<br />
语法和完全的面向对象是有代价了。<br />
所以，要啥自行车呢，下面有Python呢，不急不急&#8230;..<br />
Google Doc 没有评论机制，也就没有立刻被墙的危险，<br />
如有真心拍砖赐教者请发邮件至stcshen@gmail.com<br />
&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;<br />
2009.9.7<br />
&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;-</p>
<ul>
<li><span style="font-size: medium;"><strong>Java的基本数据类型：</strong></span></li>
</ul>
<p>Java中的数据类型被分为值类型与引用类型两类：<br />
Variable  By Datatype   ：  Primary        值 ;  Reference    引用<br />
基本类型表：</p>
<table border="1">
<tbody>
<tr valign="top">
<th valign="top">
<div>
<p><span style="font-family: Georgia;">主类型 </span></div>
</th>
<th valign="top">
<div>
<p><span style="font-family: Georgia;">大小 </span></div>
</th>
<th valign="top">
<div>
<p><span style="font-family: Georgia;">最小值 </span></div>
</th>
<th valign="top">
<div>
<p><span style="font-family: Georgia;">最大值 </span></div>
</th>
<th valign="top">
<div>
<p><span style="font-family: Georgia;">封装器类型</span></div>
</th>
</tr>
<tr valign="top">
<td>
<div>
<p><span style="font-family: Georgia;">boolean</span></div>
</td>
<td>
<div>
<p><span style="font-family: Georgia;">1-bit</span></div>
</td>
<td>
<div>
<p><span style="font-family: Georgia;">–</span></div>
</td>
<td>
<div>
<p><span style="font-family: Georgia;">–</span></div>
</td>
<td>
<div>
<p><span style="font-family: Georgia;"><strong>Boolean</strong></span></div>
</td>
</tr>
<tr valign="top">
<td>
<div>
<p><span style="font-family: Georgia;">char</span></div>
</td>
<td>
<div>
<p><span style="font-family: Georgia;">16-bit</span></div>
</td>
<td>
<div>
<p><span style="font-family: Georgia;">Unicode 0</span></div>
</td>
<td>
<div>
<p><span style="font-family: Georgia;">Unicode 2<sup>16</sup>- 1</span></div>
</td>
<td>
<div>
<p><span style="font-family: Georgia;"><strong>Character</strong></span></div>
</td>
</tr>
<tr valign="top">
<td>
<div>
<p><span style="font-family: Georgia;">byte </span></div>
</td>
<td>
<div>
<p><span style="font-family: Georgia;">8-bit</span></div>
</td>
<td>
<div>
<p><span style="font-family: Georgia;">-128</span></div>
</td>
<td>
<div>
<p><span style="font-family: Georgia;">+127</span></div>
</td>
<td>
<div>
<p><span style="font-family: Georgia;"><strong>Byte</strong></span><a name="fnB11" href="https://docs.google.com/Doc?docid=0AWTGATyPvbhtZGdneDlqaGhfMzY2ZnhyOGZjY2s&amp;hl=zh_CN#fn11"></a></div>
</td>
</tr>
<tr valign="top">
<td>
<div>
<p><span style="font-family: Georgia;">short</span></div>
</td>
<td>
<div>
<p><span style="font-family: Georgia;">16-bit</span></div>
</td>
<td>
<div>
<p><span style="font-family: Georgia;">-2<sup>15</sup></span></div>
</td>
<td>
<div>
<p><span style="font-family: Georgia;">+2<sup>15</sup> – 1</span></div>
</td>
<td>
<div>
<p><span style="font-family: Georgia;"><strong>Short</strong></span></div>
</td>
</tr>
<tr valign="top">
<td>
<div>
<p><span style="font-family: Georgia;">int</span></div>
</td>
<td>
<div>
<p><span style="font-family: Georgia;">32-bit</span></div>
</td>
<td>
<div>
<p><span style="font-family: Georgia;">-2<sup>31</sup></span></div>
</td>
<td>
<div>
<p><span style="font-family: Georgia;">+2<sup>31</sup> – 1</span></div>
</td>
<td>
<div>
<p><span style="font-family: Georgia;"><strong>Integer</strong></span></div>
</td>
</tr>
<tr valign="top">
<td>
<div>
<p><span style="font-family: Georgia;">long</span></div>
</td>
<td>
<div>
<p><span style="font-family: Georgia;">64-bit</span></div>
</td>
<td>
<div>
<p><span style="font-family: Georgia;">-2<sup>63</sup></span></div>
</td>
<td>
<div>
<p><span style="font-family: Georgia;">+2<sup>63</sup> – 1</span></div>
</td>
<td>
<div>
<p><span style="font-family: Georgia;"><strong>Long</strong></span></div>
</td>
</tr>
<tr valign="top">
<td>
<div>
<p><span style="font-family: Georgia;">float</span></div>
</td>
<td>
<div>
<p><span style="font-family: Georgia;">32-bit</span></div>
</td>
<td>
<div>
<p><span style="font-family: Georgia;">IEEE754</span></div>
</td>
<td>
<div>
<p><span style="font-family: Georgia;">IEEE754</span></div>
</td>
<td>
<div>
<p><span style="font-family: Georgia;"><strong>Float</strong></span></div>
</td>
</tr>
<tr valign="top">
<td>
<div>
<p><span style="font-family: Georgia;">double</span></div>
</td>
<td>
<div>
<p><span style="font-family: Georgia;">64-bit </span></div>
</td>
<td>
<div>
<p><span style="font-family: Georgia;">IEEE754</span></div>
</td>
<td>
<div>
<p><span style="font-family: Georgia;">IEEE754</span></div>
</td>
<td>
<div>
<p><span style="font-family: Georgia;"><strong>Double</strong></span></div>
</td>
</tr>
<tr valign="top">
<td>
<div>
<p><span style="font-family: Georgia;">void</span></div>
</td>
<td>
<div>
<p><span style="font-family: Georgia;">–</span></div>
</td>
<td>
<div>
<p><span style="font-family: Georgia;">–</span></div>
</td>
<td>
<div>
<p><span style="font-family: Georgia;">–</span></div>
</td>
<td>
<div>
<p><span style="font-family: Georgia;"><strong>Void</strong></span></div>
</td>
</tr>
</tbody>
</table>
<p>Variable By Position that is declared :  Method;       局部变量  ;Instance;<br />
实例 成员变量 区别在于 局部变量只能显式赋值，而成员变量是有默认初始值的。<br />
{<br />
public static void main(String [] args)<br />
{<br />
int i =0;    //不可以省略<br />
}<br />
static j ; //=0;  可以省略<br />
}<br />
声明的位置决定了作用域，和C++等诸多语言的内容都是大体一致的。<br />
除了给出的8种基本类型之外（void相当于空气，还有 连那八种其实java都不想要）其余的数据类型都是封装好了的类，比如 String 它们有好些个可用的<strong>方法</strong>，这也是java使用方便的一个原因。<br />
Java将所有的数据当做对象来处理,而进行对象操作通过的变量名称为“句柄”，可以将其想象成指针，不过它更加的安全，无论对其进行什么操作，它只是链接到对象的一根线而已，可连可断。<br />
而对于程序数据的存储来说，基本类型的那8种是可以直接存于程序栈中的，直接用它的名称——地址绑定进行调用。<br />
&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8211;</p>
<ul>
<li><span style="font-size: medium;"><strong>Java 保留字（分类非官方 评价和用法仅供参考）</strong>：</span></li>
</ul>
<p>每一种语言都有自己的一套关键字，所有的语法基本上均通过这些实现。<br />
<strong>基本类型关键字</strong>：<br />
boolean;  byte; char; float ;int; long; short; void;<br />
<strong>有几个没用的东西 但是 给个面子保留了下来&#8230;&#8230;</strong><br />
const(已经给final取代 )  goto （有你也别用 它是任何一个条例清晰程序的Killer）<br />
<strong>结构控制保留字:</strong><br />
break ; case ; continue; do;~while; else; for; if ; return ; switch;<br />
<strong>类与对象操作控制保留字：</strong><br />
abstract (抽象) ; extends (父类扩展); class ; implements(接口实现) ;<br />
instanceof(返回对象与类的匹配与否 ） ;  interface(接口);  new ;<br />
super(父类访问)   ;  this(本类访问) ;<br />
<strong> 字段 方法 与对象的精度，权限和存储控制：</strong><br />
继承访问权限：private ;  protected ;   default ;  public;<br />
精度控制：    strictfp(声明类中严格浮点运算)<br />
存储控制：    final (修饰对象静态不可变) ; transient (修饰的对象不需要维持)<br />
<strong> 异常处理控制：</strong><br />
try~ catch ; finally(无论如何都执行)  ;  throw (手动判断并抛出异常) ;<br />
throws（抛出块内异常 用于自动处理）;<br />
<strong>进程与效率控制：</strong><br />
synchronized(方法 对象 字段) ~ volatile（字段）-（控制多进程使用）  ;<br />
native(调用其他更高效的语言 绕过虚拟机 ^_^)<br />
&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;<br />
2009.10.6<br />
&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;</p>
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