First find a automated code-formatter that works with your language. Reason: Whatever the document says, people will inevitably break the rules. It's much easier to run code through a formatter than to nit-pick in a code review.
If you're using a language with an existing standard (e.g. Java, C#), it's easiest to use it, or at least start with it as a first draft. Sun put a lot of thought into their formatting rules; you might as well take advantage of it.
In any case, remember that much research has shown that varying things like brace position and whitespace use has no measurable effect on productivity or understandability or prevalence of bugs. Just having any standard is the key.
Counterintuitively, the fastest version, on Hotspot 8, is:
MyClass[] arr = myList.toArray(new MyClass[0]);
I have run a micro benchmark using jmh the results and code are below, showing that the version with an empty array consistently outperforms the version with a presized array. Note that if you can reuse an existing array of the correct size, the result may be different.
Benchmark results (score in microseconds, smaller = better):
Benchmark (n) Mode Samples Score Error Units
c.a.p.SO29378922.preSize 1 avgt 30 0.025 ▒ 0.001 us/op
c.a.p.SO29378922.preSize 100 avgt 30 0.155 ▒ 0.004 us/op
c.a.p.SO29378922.preSize 1000 avgt 30 1.512 ▒ 0.031 us/op
c.a.p.SO29378922.preSize 5000 avgt 30 6.884 ▒ 0.130 us/op
c.a.p.SO29378922.preSize 10000 avgt 30 13.147 ▒ 0.199 us/op
c.a.p.SO29378922.preSize 100000 avgt 30 159.977 ▒ 5.292 us/op
c.a.p.SO29378922.resize 1 avgt 30 0.019 ▒ 0.000 us/op
c.a.p.SO29378922.resize 100 avgt 30 0.133 ▒ 0.003 us/op
c.a.p.SO29378922.resize 1000 avgt 30 1.075 ▒ 0.022 us/op
c.a.p.SO29378922.resize 5000 avgt 30 5.318 ▒ 0.121 us/op
c.a.p.SO29378922.resize 10000 avgt 30 10.652 ▒ 0.227 us/op
c.a.p.SO29378922.resize 100000 avgt 30 139.692 ▒ 8.957 us/op
For reference, the code:
@State(Scope.Thread)
@BenchmarkMode(Mode.AverageTime)
public class SO29378922 {
@Param({"1", "100", "1000", "5000", "10000", "100000"}) int n;
private final List<Integer> list = new ArrayList<>();
@Setup public void populateList() {
for (int i = 0; i < n; i++) list.add(0);
}
@Benchmark public Integer[] preSize() {
return list.toArray(new Integer[n]);
}
@Benchmark public Integer[] resize() {
return list.toArray(new Integer[0]);
}
}
You can find similar results, full analysis, and discussion in the blog post Arrays of Wisdom of the Ancients. To summarize: the JVM and JIT compiler contains several optimizations that enable it to cheaply create and initialize a new correctly sized array, and those optimizations can not be used if you create the array yourself.
Best Answer
If there are standards evident in the code, you should stick to them. If there aren't, start introducing your own.