java runtime_error ai_generated true

java.lang.UnsupportedOperationException: null (or with message: ImmutableList does not support modification)

ID: java/unsupportedoperationexception-immutable-list

Also available as: JSON · Markdown · 中文
95%Fix Rate
90%Confidence
1Evidence
2023-03-05First Seen

Version Compatibility

VersionStatusIntroducedDeprecatedNotes
Java 9 active — — —
Java 11 active — — —
Java 17 active — — —
Java 21 active — — —
Guava 31.x active — — —

Root Cause

This error occurs when an attempt is made to modify an immutable collection (e.g., List.of(), Collections.unmodifiableList(), or Guava's ImmutableList) by calling methods like add(), remove(), or set().

generic

中文

当尝试通过调用add()、remove()或set()等方法修改不可变集合（例如List.of()、Collections.unmodifiableList()或Guava的ImmutableList）时发生。

Official Documentation

https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/lang/UnsupportedOperationException.html

Workarounds

  1. 95% success Create a mutable copy of the immutable list before modification: `List<String> mutableList = new ArrayList<>(immutableList); mutableList.add("new element");` 
    Create a mutable copy of the immutable list before modification: `List<String> mutableList = new ArrayList<>(immutableList); mutableList.add("new element");`
  2. 90% success Use the builder pattern for mutable collections from the start: `List<String> list = new ArrayList<>(List.of("a", "b"));` or use `Stream.collect(Collectors.toList())` which returns a mutable list. 
    Use the builder pattern for mutable collections from the start: `List<String> list = new ArrayList<>(List.of("a", "b"));` or use `Stream.collect(Collectors.toList())` which returns a mutable list.
  3. 90% success For Guava ImmutableList, use the copyOf() method to create a mutable ArrayList: `List<String> mutableList = new ArrayList<>(ImmutableList.copyOf(originalList));` 
    For Guava ImmutableList, use the copyOf() method to create a mutable ArrayList: `List<String> mutableList = new ArrayList<>(ImmutableList.copyOf(originalList));`

中文步骤

  1. Create a mutable copy of the immutable list before modification: `List<String> mutableList = new ArrayList<>(immutableList); mutableList.add("new element");`
  2. Use the builder pattern for mutable collections from the start: `List<String> list = new ArrayList<>(List.of("a", "b"));` or use `Stream.collect(Collectors.toList())` which returns a mutable list.
  3. For Guava ImmutableList, use the copyOf() method to create a mutable ArrayList: `List<String> mutableList = new ArrayList<>(ImmutableList.copyOf(originalList));`

Dead Ends

Common approaches that don't work:

  1. Catching the exception and ignoring it 80% fail

    The collection remains unmodified; ignoring the exception does not achieve the intended mutation and may lead to data inconsistencies.

  2. Using Arrays.asList() instead of List.of() but still calling add() 70% fail

    Arrays.asList() returns a fixed-size list backed by the array; add() still throws UnsupportedOperationException because the size is fixed.

  3. Casting the list to ArrayList and modifying it 90% fail

    The underlying object is not an ArrayList; casting will throw ClassCastException.