Where should I initialize the array in a for-each loop?

There are pluses to each way of writing your loop:

• The first way is more debuggable: you can set a breakpoint on the for, and inspect words
• The second way avoids introducing a name words into the namespace, so you can use the name elsewhere.

As far as performance and readability go, both ways are equally good: the split will be called once before the start of the loop, so there are no performance or memory usage consequences to using the second code snippet.

Since, there is no difference in terms of performance I think:

String[] words = text.split(" ");
for (String s : words)
{...}

should be used because you can still use the words generated by text.split(" ") for further data manipulation. In the second approach, you can only the words inside the loop.

In the following code getList() is only called once. So I think there is no differences performance-wise about the 2 ways you asked.

class Test {

    static int[] list = {1,2,3,4,5};

    static int[] getList() {
        System.out.println("getList executed");
        return list;
    }

    public static void main(String[] args) {
        for(int n: getList()) {
            System.out.println("n = "+n);
        }
    }
}

Output:

getList executed
n = 1
n = 2
n = 3
n = 4
n = 5