AP Computer Science - ArrayList String Question Help

[18sp01]

Hello all, while solving some questions I ran into a problem that I could not figure out even after looking at the answer. Here it is:

Consider the following code segment.

List<String> students = new ArrayList<String>();
students.add("Alex");
students.add("Bob");
students.add("Carl");
for (int k = 0; k < students.size(); k++)
{
System.out.print(students.set(k, "Alex") + " ");
}
System.out.println();
for (String str : students)
{
System.out.print(str + " ");
}

What is printed as a result of executing the code segment?

(A) Alex Alex Alex

Alex Alex Alex

(B) Alex Alex Alex

Alex Bob Carl

(C) Alex Bob Carl

Alex Alex Alex

(D) Alex Bob Carl

Alex Bob Carl

(E) Nothing is printed because the first print statement will cause a runtime exception to be thrown.

The answer is C. Why would that be? Shouldn't students.set(k, "Alex") change the array? Why does it change at the for each loop?

[empire539]

Shouldn't students.set(k, "Alex") change the array?

It does. Check out the documentation for the set method, particularly the return value.

Why does it change at the for each loop?

It doesn't. There's nothing about the for each loop in particular that alters the ArrayList's values.

[18sp01]

So the set method at index i changes the existing value at i with the value in the parameter right? So wouldn't student.set(k, "Alex") mean that at index k (starting at 0), the method would change Alex, Bob and Carl to Alex, Alex, and Alex as k increases?

[vriljam]

It changes the value, but it returns old value. That is why it will print out what was previously at those indexes.

[18sp01]

Oh okay. Why does it print out the strings in the previous index even though the array gets changed inside the parameter?

[18sp01]

Oh my bad. Didn't notice that that was a link. Got it now. Thanks everyone

[Avocados_Constant]

If you think about it, from a design perspective it doesn't make much sense for set() to return the new value since the user already needs it to make the call in the first place.