3  

A direct path will tend to perform better than one using the more general descendant-or-self (//) axis, however:

然而，使用更一般的后代-或-自我(/)軸，直接路徑的性能往往比直接路徑更好:

• Implementations could vary (but as a general rule, direct paths perform better).
• 實現可能會有所不同(但作為一般規則，直接路徑執行得更好)。
• The difference can be minor enough not to matter, especially for small documents.
• 差異可能很小，不重要，特別是對於小文檔。
• As with all performance concerns, measure before optimizing to avoid expending effort in areas other than true bottlenecks.
• 與所有性能問題一樣，在優化之前進行度量，以避免在真正的瓶頸之外的領域花費精力。

1  

I would imagine that /root/a/b/c/d/e would be more efficient, because in the first case, the XPath processor can eliminate a lot of branches, whereas in the second case (//e) the XPath processor has to search the entire document tree.

我認為/root/a/b/c/d/e會更有效，因為在第一種情況下，XPath處理器可以消除很多分支，而在第二種情況下(//e)， XPath處理器必須搜索整個文檔樹。

You should write a small Java program that excersizes the two different ways, and then see how long it takes to run 1000 loops.

您應該編寫一個小的Java程序，從中摘錄兩種不同的方法，然后查看運行1000個循環需要多長時間。

1  

Understanding the leading / and // constructs is very important.

理解領導/和//構念是非常重要的。

A leading / starts a path that is always relevant to the root node. Therefore, even though we are searching a sub-node, the XPath:

引導/啟動始終與根節點相關的路徑。因此，即使我們正在搜索一個子節點，XPath:

root/a/b/c

... will still return every c node in your XML document even though they are not descendants of the first c node. Likewise, the XPath:

…將仍然返回XML文檔中的每個c節點，即使它們不是第一個c節點的后代。同樣,XPath:

//e/

... will still return every e node in your XML document, not just the descendants of your first c node.

…將仍然返回XML文檔中的每個e節點，而不僅僅是第一個c節點的后代。