How to remove and set from List in java?

Question

In java I have this function:

public List<String> seperatekeys(String text) {
    String[] keys = text.split("and");
    List<String> words = Arrays.asList(keys);

    ListIterator<String> iter = words.listIterator();
    while (iter.hasNext()) {
        String currentWord = iter.next().trim();
        if (currentWord.equals("")) {
            iter.remove();
        } else {
            iter.set(currentWord);
        }
    }

    return words;
}

But when I do a remove(), it crashes saying unsupportedoperationerror.

Anyone know how to fix it?

Thanks

`Arrays.asList()` returns a `List` that cannot be modified (at runtime) — awksp, Jun 01 '14 at 02:49
Pass the result of `Arrays.asList()` into the constructor of a different list — awksp, Jun 01 '14 at 02:53
@shekhar If you notice, the error is with `remove()`. I fail to see how comparing to `null` would fix that. — awksp, Jun 01 '14 at 02:56
so your saying an empty string when compared to null will return a true? — omega, Jun 01 '14 at 02:56
Create an empty ArrayList, iterate over the array directly, adding those elements you want to keep instead — MadProgrammer, Jun 01 '14 at 02:57
@user35...: That worked nicely, although seems inefficient... — omega, Jun 01 '14 at 02:57
`List words = new LinkedList(Arrays.asList(keys));` http://stackoverflow.com/a/2965808/3574819 — FuzzyTree, Jun 01 '14 at 03:02

awksp · Accepted Answer · 2014-06-01T03:11:36.393

5

The issue is that Arrays#asList() returns an ArrayList implementation that inherits remove() from AbstractList. The implementation of remove() in AbstractList is this:

public E remove(int index) {
    throw new UnsupportedOperationException();
}

And because the iterator uses the list's iterator to perform its remove() method, you end up with the exception.

You have a few solutions here. You can either pass the result of Arrays#asList() to an ArrayList constructor:

List<String> words = new ArrayList<>(Arrays.asList(keys));

Now, you can iterate over the resulting List and remove the elements you want.

Or, asMadProgrammer stated, you can take the opposite approach and iterate over the array and add the elements you want to keep:

List<String> words = new ArrayList<>();
for (String s : keys) {
    String currentWord = s.trim();
    if (!currentWord.equals("")) {
        words.add(currentWord);
    }
}

edited Jun 01 '14 at 03:11

answered Jun 01 '14 at 03:02

awksp

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Should it be `new ArrayList` instead of `new ArrayList<>`? – Unihedron Jun 01 '14 at 03:05
@user3580294-Nice answer! – Am_I_Helpful Jun 01 '14 at 03:06
@Unihedron No. The former is a raw type and should be avoided if at all possible. The latter is generic and is, for the most part, type-safe. – awksp Jun 01 '14 at 03:06
You're directly assigning it to a `List`. The raw type is inferred to ``. – Unihedron Jun 01 '14 at 03:19
@Unihedron No inference takes place when dealing with raw types, because no generic checks are performed at all. – awksp Jun 01 '14 at 03:26

How to remove and set from List in java?

1 Answers1