I have a Java program which cares about efficiency. There I use XPaths.
我有一个关心效率的Java程序。我使用xpath。
In XPath I can select elements starting from root
在XPath中，我可以从root开始选择元素
/root/a/b/c/d/e
or use the descendent-or-self axis:
或者使用后代-自我轴:
//e
What will be most efficient method among these two?
这两种方法中最有效的方法是什么?
3 个解决方案
#1
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(/)轴，直接路径的性能往往比直接路径更好:
- Implementations could vary (but as a general rule, direct paths perform better).
- 实现可能会有所不同(但作为一般规则，直接路径执行得更好)。
- The difference can be minor enough not to matter, especially for small documents.
- 差异可能很小，不重要，特别是对于小文档。
- As with all performance concerns, measure before optimizing to avoid expending effort in areas other than true bottlenecks.
- 与所有性能问题一样，在优化之前进行度量，以避免在真正的瓶颈之外的领域花费精力。
#2
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.
我认为/root/a/b/c/d/e会更有效，因为在第一种情况下，XPath处理器可以消除很多分支，而在第二种情况下(//e)， XPath处理器必须搜索整个文档树。
You should write a small Java program that excersizes the two different ways, and then see how long it takes to run 1000 loops.
您应该编写一个小的Java程序，从中摘录两种不同的方法，然后查看运行1000个循环需要多长时间。
#3
1
Understanding the leading / and // constructs is very important.
理解领导/和//构念是非常重要的。
A leading / starts a path that is always relevant to the root node. Therefore, even though we are searching a sub-node, the XPath:
引导/启动始终与根节点相关的路径。因此，即使我们正在搜索一个子节点，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:
…将仍然返回XML文档中的每个c节点，即使它们不是第一个c节点的后代。同样,XPath:
//e/
... will still return every e node in your XML document, not just the descendants of your first c node.
…将仍然返回XML文档中的每个e节点，而不仅仅是第一个c节点的后代。
#1
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(/)轴，直接路径的性能往往比直接路径更好:
- Implementations could vary (but as a general rule, direct paths perform better).
- 实现可能会有所不同(但作为一般规则，直接路径执行得更好)。
- The difference can be minor enough not to matter, especially for small documents.
- 差异可能很小，不重要，特别是对于小文档。
- As with all performance concerns, measure before optimizing to avoid expending effort in areas other than true bottlenecks.
- 与所有性能问题一样，在优化之前进行度量，以避免在真正的瓶颈之外的领域花费精力。
#2
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.
我认为/root/a/b/c/d/e会更有效，因为在第一种情况下，XPath处理器可以消除很多分支，而在第二种情况下(//e)， XPath处理器必须搜索整个文档树。
You should write a small Java program that excersizes the two different ways, and then see how long it takes to run 1000 loops.
您应该编写一个小的Java程序，从中摘录两种不同的方法，然后查看运行1000个循环需要多长时间。
#3
1
Understanding the leading / and // constructs is very important.
理解领导/和//构念是非常重要的。
A leading / starts a path that is always relevant to the root node. Therefore, even though we are searching a sub-node, the XPath:
引导/启动始终与根节点相关的路径。因此，即使我们正在搜索一个子节点，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:
…将仍然返回XML文档中的每个c节点，即使它们不是第一个c节点的后代。同样,XPath:
//e/
... will still return every e node in your XML document, not just the descendants of your first c node.
…将仍然返回XML文档中的每个e节点，而不仅仅是第一个c节点的后代。