Strings in a List

[Luigi Plinge]

Can someone please explain why the "s haven't gone away when I try to get rid of them in the List?

import java.util.Arrays;
import java.util.List;

public class NewClass {

    public static void main(String[] args) {
        String s = "\"Hi\"";
        System.out.println(s);
        s = s.replace("\"", "");
        System.out.println(s);


        List<String> names = Arrays.asList(new String[]{"\"Yo\""});
        for (String n : names) {
            n = n.replace("\"", "");
        }
        System.out.println(names.get(0));
    }
}

Output currently is:

"Hi"
Hi
"Yo"

[Darryl Burke]

Because in your enhanced for loop, the variable n is a local variable which is reassigned to a new String returned from n.replace("\"", "") and doesn't affect the value stored in the List. The loop is functionally equivalent to

for (int i = 0; i < names.size(); i++) {
  String n = names.get(i);
  n = n.replace("\"", "");
}

You can easily see that this won't change the value of the String at names.get(i).

[Rob Spoor]

Luigi Plinge wrote:

List<String> names = Arrays.asList(new String[]{"\"Yo\""});

On a side note, Java 5.0 added varargs and that's enabled for Arrays.asList too. So you can also write the following:

List<String> names = Arrays.asList("\"Yo\"");

In the background the exact same thing happens, but this is easier to read and write.

[Luigi Plinge]

Thanks, I guess I need to change the 2nd part to

        List<String> names = Arrays.asList("\"Yo\"");
        for (int i = 0; i < names.size(); i++) {
            String n = names.get(i);
            n = n.replace("\"", "");
            names.set(i, n);
        }
        System.out.println(names.get(0));

Is there a way to do this while retaining the enhanced for loop?

[Ernie Mcracken]

I would probably be inclined to get the iterator for your list and use that.

[Darryl Burke]

A String is immutable, and a List contains references to its contents. Any amount of fudging around won't change the String referenced from the List.

The only valid approach will be to remove the string form the list, and add the parsed string in its place (or at the end if order isn't an issue).

[Luigi Plinge]

Ernie Mcracken wrote:I would probably be inclined to get the iterator for your list and use that.

I haven't used iterators before but I think you just run into the same problem as with enhanced for:

        for (Iterator<String> it = names.iterator(); it.hasNext(); ) {
            String n = it.next().replace("\"", "");
            names.set(?????, n)
        }

So I guess enhanced-for is out and we just have to step through using a standard for loop.

[Ernie Mcracken]

Ah sorry I meant that to say use ListIterator,

   List<String> list = new ArrayList<String>();

            list.add("\"Yo\"");
            list.add("\"Hi\"");
            

            ListIterator<String> iterator = list.listIterator();

            while (iterator.hasNext()){
               iterator.set(iterator.next().replaceAll("\"", ""));
            }

            iterator = list.listIterator();

            while (iterator.hasNext()){
                System.out.println(iterator.next());
            }

Output is

Yo
Hi

[Matthew Brown]

Luigi Plinge wrote:So I guess enhanced-for is out and we just have to step through using a standard for loop.

Unless you want to create a new List:

List<String> editedNames = new ArrayList<String>();
for(String n : names) {
    editedNames.add(n.replace("\"", ""));
}
names = editedNames;

[Luigi Plinge]

Thanks! I didn't know about the ListIterator's set method.

Using for:

        for (ListIterator<String> it = names.listIterator(); it.hasNext(); ) {
            it.set(it.next().replace("\"", ""));
        }

which is equivalent to

        for (int i = 0; i < names.size(); i++) {
            names.set(i, names.get(i).replace("\"", ""));
        }

although I suppose a while loop is more readable.

Matthew - yes, that's another good idea, thanks!