These sentences are equal:
myString != nullmyString.length() > 0! myString.equals("")
Which is the most efficient? (Java 1.4)
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6It doesn't matter. Move on to something important.JohnFx– JohnFx2010-07-30 22:58:08 +00:00Commented Jul 30, 2010 at 22:58
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4@JohnFx: something important like, say, the meaning of life? Anyway, what IS important is that unlike stated in the questions, these are NOT EQUAL AT ALL.NoozNooz42– NoozNooz422010-07-30 23:07:17 +00:00Commented Jul 30, 2010 at 23:07
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2 Answers
Those aren't all equivalent - a null reference is not the same as an empty string.
The null test will likely be the most efficient because all the others at least require first finding out whether or not the reference is null.
The the best way to find out is to measure the performance:
public static void main(String[] args)
{
String myString = "foo";
int a = 0;
for (int i = 0; i < 100000000; ++i)
{
//if (myString != null)
//if (myString.length() > 0)
if (!myString.equals(""))
{
a++;
}
}
System.out.println(a);
}
The results:
myString != null : 0.61s
myString.length() > 0 : 0.67s
!myString.equals("") : 2.82s
So a null test and a length test take almost the same amount of time, but testing for equality with an empty string takes more than four times longer. Note that I tested on a slightly newer version of Java than you are using, so you should run the tests yourself to see if you get the same results.
Comments
They are not equivalent. If myString is null the 2nd one will throw a NullPointerException.
That said, (myString != null && myString.length() != 0) might be slightly more efficient than ("".equals(myString)). But they'll still react differently to myString being null.
