aslist

asList, commonly encountered as Arrays.asList in the Java standard library, is a static generic method in java.util.Arrays. It returns a List<T> that is backed by a given array, providing a convenient way to use the List interface without copying elements.

The list produced by asList has a fixed size equal to the length of the underlying array. You can read and write elements via get and set, and you can use standard list operations such as contains or indexOf. However, you cannot add or remove elements from this list; any attempt to structurally modify it (for example, add, remove, or clear) results in an UnsupportedOperationException. Because the list is backed by the original array, changes made through the list are reflected in the array, and changes to the array are reflected in the list.

A common pitfall involves primitive arrays. When a primitive array is passed, asList treats it as a single element of type int[] (or the corresponding primitive array type), producing a List<int[]> with one element rather than a List<Integer>. To obtain a List<Integer>, provide an array of wrapper types (e.g., new Integer[]{1, 2, 3}) or use a stream to box values.

Use cases for asList include adapting a fixed-size array to APIs that require a List without copying data. It is unsuitable when a truly resizable list is needed. For a resizable list, a common workaround is new ArrayList<>(Arrays.asList(array)). For immutable needs, newer Java versions offer alternatives like List.of, which does not reflect an underlying array.