Common Pitfalls When Using Java List Collections

Background

List is a collection frequently used in Java development, but it has its own limitations and errors. The following sections illustrate common pitfalls.

Arrays.asList returns a List that does not support add or remove operations

String[] array = new String[]{"a","b","c"};
System.out.println(array.length);
List<string> strings = Arrays.asList(array);
strings.add("d");
strings.remove(1);

Both add and remove cause java.lang.UnsupportedOperationException because the list returned by Arrays.asList is not a regular ArrayList but a fixed‑size view.

Directly iterating a List and removing elements also throws an error

String[] array = new String[]{"a","b","c"};
System.out.println(array.length);
List<string> strings = Arrays.asList(array);

for (int i = 0; i < strings.size(); i++) {
    strings.remove(i);
}

Removing elements while iterating over the list produced by Arrays.asList triggers the same UnsupportedOperationException.

Unexpected behavior when converting primitive arrays with Arrays.asList

When developers need to convert an array to a List, they often use Arrays.asList. However, for primitive type arrays the result is not what is expected.

int[] array = new int[]{1,2,3};
System.out.println(array.length);
List<int[]> ints = Arrays.asList(array);
System.out.println(ints.size());

The printed results are 3 and 1. The list contains a single element of type int[], meaning the whole primitive array is treated as one object rather than being split into individual integers.

These examples demonstrate why developers should be cautious when using Arrays.asList with mutable operations or primitive arrays.