Question

(A question for those who know well the JVM compilation and optimization tricks… 🙂

Is there any of the “for” and “foreach” patterns clearly superior to the other?

Consider the following two examples:

public void forLoop(String[] text)
{
    if (text != null)
    {
        for (int i=0; i<text.length; i++)
        {
            // Do something with text[i]
        }
    }
}

public void foreachLoop(String[] text)
{
    if (text != null)
    {
        for (String s : text)
        {
            // Do something with s, exactly as with text[i]
        }
    }
}

Is forLoop faster or slower than foreachLoop?

Assuming that in both cases the text array did not need any do sanity checks, is there a clear winner or still too close to make a call?

EDIT: As noted in some of the answers, the performance should be identical for arrays, whereas the “foreach” pattern could be slightly better for Abstract Data Types like a List. See also this answer which discusses the subject.

Answer 1

From section 14.14.2 of the JLS:

Otherwise, the Expression necessarily has an array type, T[]. Let L1 … Lm be the (possibly empty) sequence of labels immediately preceding the enhanced for statement. Then the meaning of the enhanced for statement is given by the following basic for statement:

T[] a = Expression;
L1: L2: ... Lm:
for (int i = 0; i < a.length; i++) {
        VariableModifiersopt Type Identifier = a[i];
        Statement
}

In other words, I’d expect them to end up being compiled to the same code.

There’s definitely a clear winner: the enhanced for loop is more readable. That should be your primary concern – you should only even consider micro-optimizing this sort of thing when you’ve proved that the most readable form doesn’t perform as well as you want.