blocks|key|3050610|text|正如您正确猜测的那样，Order+and+Export选项卡显示了将包含在项目构建路径中的库的顺序。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|3050611|使用按钮up和down，您可以根据项目需要调整库的顺序。|3050612|entityMap^0|B|G|0|4|2|7|4|0^^$0|@$1|2|3|4|5|6|7|J|8|@$9|K|A|L|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|M|8|@$9|N|A|O|B|C]|$9|P|A|Q|B|C]]|D|@]|E|$]]|$1|H|3|-4|5|6|7|R|8|@]|D|@]|E|$]]]|I|$]]

<code>Order and Export</code> tab as your rightly guessed shows the order of libraries which will be included in your project build path.

Using the buttons <code>up</code> and <code>down</code> you can adjust your libraries order according to your project needs.

blocks|key|204329|text|为了回答您的特定问题，如果要将此项目添加为另一个Java项目的依赖项，则在运行另一个项目时，将使用顺序来解析此项目中的类和包。这些类和包导出到另一个正在运行的项目的类路径。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|204330|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

To answer your specific question, if this project were to be added as a dependency for another Java project, the order would be used to resolve classes and packages in this project when running the other project. Those classes and packages are said to be exported to/for the other running project's class path.

blocks|key|2837750|text|此选项卡似乎具有双重功能(请参阅bottom+of+this+help+page了解更多细节)。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|2837751|一方面，它作为项目构建中使用的资源的解析顺序(“顺序”部分)。另一方面，它还用于定义此构建路径的哪些部分将贡献给相关项目(在“项目”选项卡中列出此项目以查看此首选项面板的项目)构建路径(“导出”部分)。|2837752|后一种功能是复选框存在于左侧的原因，正如您所问的那样(请注意，不能取消选中'-‘符号，因为在此项目中定义的源文件不能被取消选择，如帮助文件中所述)。如果一个依赖项目期望来自贡献项目的一些资源，如果贡献项目没有导出该资源，那么该依赖项目将不会编译/运行。|2837753|编辑:请参阅this+SO+post以进行验证。|2837754|entityMap|0|LINK|mutability|MUTABLE|url|http://help.eclipse.org/juno/index.jsp?topic=/org.eclipse.jdt.doc.user/reference/ref-properties-build-path.htm|1|https://stackoverflow.com/questions/2737486/what-is-the-use-of-order-and-export-tab-in-java-build-path^0|G|O|0|0|0|0|6|C|1|0^^$0|@$1|2|3|4|5|6|7|T|8|@]|9|@$A|U|B|V|1|W]]|C|$]]|$1|D|3|E|5|6|7|X|8|@]|9|@]|C|$]]|$1|F|3|G|5|6|7|Y|8|@]|9|@]|C|$]]|$1|H|3|I|5|6|7|Z|8|@]|9|@$A|10|B|11|1|12]]|C|$]]|$1|J|3|-4|5|6|7|13|8|@]|9|@]|C|$]]]|K|$L|$5|M|N|O|C|$P|Q]]|R|$5|M|N|O|C|$P|S]]]]

This tab seems to pull double duty (see <a href="http://help.eclipse.org/juno/index.jsp?topic=/org.eclipse.jdt.doc.user/reference/ref-properties-build-path.htm" rel="nofollow noreferrer">bottom of this help page</a> for small amount of detail). 

On one hand, it functions as the order of resolution for resources used in the building of the project in question (the "Order" part). On the other, it also serves to define what parts of this build path are contributed to dependent projects' (those listing this project in the "projects" tab for their view of this preference panel) build paths (the "Export" part). 

This latter function is why the checkboxes exist on the left hand side, as you ask (note that the '-' signs cannot be unchecked, as source files defined in this project cannot be deselected, as stated in help file). A dependent project that expects some resource from the contributing project will not compile/run if the contributing project doesn't export that resource.

EDIT: see <a href="https://stackoverflow.com/questions/2737486/what-is-the-use-of-order-and-export-tab-in-java-build-path">this SO post</a> for corroboration.

blocks|key|204357|text|在一个案例中，我发现这很有用。我不得不使用一个sun.*类的IBM+jar。这个类也存在于本地jre中，但我的要求是使用IBM的类。但是默认情况下，编译器只引用本地jdk类。在eclipse+order+and+export选项卡中，我将外部jar移到了JRE库的前面。现在，编译器将引用来自IBM+jar的类，而不是本地JRE。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|204358|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

There is one case where-in I found this useful. I had to use a sun.* class of an IBM jar. This class was also present in local jre, but my requirement was to use IBM's class. But by default,the compiler would refer the local jdk class only. 
In the eclipse order and export tab, I moved the external jar ahead of the JRE lib. Now, the compiler would refer to the class from IBM jar instead of local JRE.

blocks|key|206001|text|来自Ilja+Preuss的Coderanch的一个非常好的例子|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|206002|206003|假设项目A的构建路径中有junit.jar。项目B依赖于项目A。|blockquote|206004|206005|现在，您可以在项目B中编写一个junit测试。如果项目A导出junit.jar，则项目B可以在编译时使用它-不需要更多的操作。如果A没有导出它，B就不知道它--你也必须显式地把它放到它的构建路径中。|206006|entityMap|0|LINK|mutability|MUTABLE|url|http://www.coderanch.com/forums/user/profile/16595|1|http://www.coderanch.com/t/104274/vc/Order-Export-tab-Java-Build^0|2|B|0|E|9|1|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@]|9|@$A|V|B|W|1|X]|$A|Y|B|Z|1|10]]|C|$]]|$1|D|3|-4|5|6|7|11|8|@]|9|@]|C|$]]|$1|E|3|F|5|G|7|12|8|@]|9|@]|C|$]]|$1|H|3|-4|5|6|7|13|8|@]|9|@]|C|$]]|$1|I|3|J|5|6|7|14|8|@]|9|@]|C|$]]|$1|K|3|-4|5|6|7|15|8|@]|9|@]|C|$]]]|L|$M|$5|N|O|P|C|$Q|R]]|S|$5|N|O|P|C|$Q|T]]]]

a very good example from <a href="http://www.coderanch.com/t/104274/vc/Order-Export-tab-Java-Build" rel="noreferrer">Coderanch</a> by <a href="http://www.coderanch.com/forums/user/profile/16595" rel="noreferrer">Ilja Preuss</a>

<blockquote>
 Say you have junit.jar in the build path of project A. Project B
 depends on project A.
 
 Now you write a junit test in project B. If project A exports
 junit.jar, project B can use it at compile time - no more action
 necessary. If A doesn't export it, B doesn't know about it - you will
 have to explicitely put it into its build path, too.
</blockquote>

<img src="https://i.stack.imgur.com/gFYoA.png" alt="enter image description here">

What's the use of "Order and Export" tab in "Java Build Path" dialog box?
By the name 'order', I can guess that JRE System library is searched before Plug-in Dependencies, but why do we have 'Export' in Build Path ? And what's it for the button left side of the elements? 

<h2>ADDED</h2>

It's the example that I borrowed from <a href="https://rads.stackoverflow.com/amzn/click/com/0321288157" rel="noreferrer" rel="nofollow noreferrer">Eclipse distilled</a>.

The orderes.webapp depends on orders, but it's likely to use the classes defined in ubl and catalog. 

<img src="https://i.stack.imgur.com/6mhyX.png?width=100pt" alt="enter image description here">

In such a case, orders can export catalog and ubl so that the packages that depends on it can use catalog and ubl. 

<img src="https://i.stack.imgur.com/3i6lN.png" alt="enter image description here">

And something more about "Order and Export".

<ol>
<li>The check of the left side button modifies the <code>.classpath</code> file to add <code>exported=true</code> such as <code>&lt;classpathentry exported="true" kind="lib" path="lib/log4j-1.2.7.jar"/&gt;</code>. </li>
<li>The src is always checked, and you can't uncheck it. </li>
</ol>

<h3>References</h3>

<ul>
<li><a href="https://stackoverflow.com/questions/13960556/interpreting-eclipse-classpath-file">Interpreting eclipse .classpath file. What does &#39;kind=&quot;con&quot;&#39; and &#39;exported=&quot;true&quot;&#39; mean?</a></li>
<li><a href="http://www.informit.com/articles/article.aspx?p=367962" rel="noreferrer">Configuring an Eclipse Java Project</a></li>
<li><a href="http://help.eclipse.org/juno/index.jsp?topic=/org.eclipse.jdt.doc.user/reference/ref-properties-build-path.htm" rel="noreferrer">Java Build Path</a></li>
</ul>

The "Order and Export" tab in "Java Build Path"

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​​"Java Build Path“对话框中的"Order and Export”选项卡有什么用？通过名称'order'，我可以猜到JRE系统库在插件依赖项之前被搜索，但是为什么我们在构建路径中有'Export‘？元素左边的按钮是什么？已添加这是我从借来的例子。orderes.webapp依赖于订单，但它可能使用ub...

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