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3474687
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2010-08-13T07:16:18.730
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2010-08-13T07:52:17.653
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2010-08-13T07:52:17.653
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22656
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3474578
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2
Score
11
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text
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In .NET, <code>Substring</code> is O(n) rather than the O(1) of Java. This is because in .NET, the String object contains all the actual character data itself1 - so taking a substring involves copying all the data within the new substring. In Java, <code>substring</code> can just create a new object referring to the original char array, with a different starting index and length. There are pros and cons of each approach: <ul> <li>.NET's approach has better cache coherency, creates fewer objects2, and avoids the situation where one small substring prevents a very large <code>char[]</code> being garbage collected. I believe in some cases it can make interop very easy too, internally.</li> <li>Java's approach makes taking a substring very efficient, and probably some other operations too</li> </ul> There's a little more detail in my <a href="http://csharpindepth.com/Articles/General/Strings.aspx" rel="noreferrer">strings article</a>. As for the general question of avoiding performance pitfalls, I think I should have a canned answer ready to cut and paste: make sure your architecture is efficient, and implement it in the most readable way you can. Measure the performance, and optimise where you find bottlenecks. <hr> 1 Incidentally, this makes <code>string</code> very special - it's the only non-array type whose memory footprint varies by instance within the same CLR. 2 For small strings, this is a big win. It's bad enough that there's all the overhead of one object, but when there's an extra array involved as well, a single-character string could take around 36 bytes in Java. (That's a "finger-in-the-air" number - I can't remember the exact object overheads. It will also depend on the VM you're using.)
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1. POComparison of substring operation performance between .NET and Java
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1. USJon Skeet
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1. USJon Skeet
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