If you use String concatenation in a loop, something like this, String s = “”; for (int i = 0; i < 100; i++) { s += “, ” + i; } then you should use a StringBuilder (not StringBuffer) instead of a String, because it is much faster and consumes less memory. If you … Read more
You could also try EXISTS: SELECT EXISTS(SELECT * FROM table1 WHERE …) and per the documentation, you can SELECT anything. Traditionally, an EXISTS subquery starts with SELECT *, but it could begin with SELECT 5 or SELECT column1 or anything at all. MySQL ignores the SELECT list in such a subquery, so it makes no … Read more
Usually not. For virtual methods, HotSpot keeps track of whether the method has actually been overridden, and is able to perform optimizations such as inlining on the assumption that a method hasn’t been overridden – until it loads a class which overrides the method, at which point it can undo (or partially undo) those optimizations. … Read more
As others have said, the issue is the store to the memory location in the array: x[i][j]. Here’s a bit of insight why: You have a 2-dimensional array, but memory in the computer is inherently 1-dimensional. So while you imagine your array like this: 0,0 | 0,1 | 0,2 | 0,3 —-+—–+—–+—- 1,0 | 1,1 … Read more
[Executive Summary: Use ++i if you don’t have a specific reason to use i++.] For C++, the answer is a bit more complicated. If i is a simple type (not an instance of a C++ class), then the answer given for C (“No there is no performance difference”) holds, since the compiler is generating the … Read more
The problem with taking IEnumerable as a parameter is that it tells callers “I wish to enumerate this”. It doesn’t tell them how many times you wish to enumerate. I can change the objects parameter to be List and then avoid the possible multiple enumeration but then I don’t get the highest object that I … Read more
There’s an old trick to do this with only one comparison/branch. Whether it’ll really improve speed may be open to question, and even if it does, it’s probably too little to notice or care about, but when you’re only starting with two comparisons, the chances of a huge improvement are pretty remote. The code looks … Read more
For just a few items, the difference is small. If you have many items you should definitely use a switch. If a switch contains more than five items, it’s implemented using a lookup table or a hash list. This means that all items get the same access time, compared to a list of if:s where … Read more
According to Pippenger [1996], when comparing a Lisp system that is purely functional (and has strict evaluation semantics, not lazy) to one that can mutate data, an algorithm written for the impure Lisp that runs in O(n) can be translated to an algorithm in the pure Lisp that runs in O(n log n) time (based … Read more
Patrick Smacchia blogged about this last month, with the following conclusions: for loops on List are a bit more than 2 times cheaper than foreach loops on List. Looping on array is around 2 times cheaper than looping on List. As a consequence, looping on array using for is 5 times cheaper than looping on … Read more