Hi Jonathan, src/java.base/share/classes/java/util/ResourceBundle.java
2490 public static class Control { 2491 /** 2492 * The default format <code>List</code>, which contains the strings 2493 * <code>"java.class"</code> and <code>"java.properties"</code>, in 2494 * this order. This <code>List</code> is {@linkplain 2495 * Collections#unmodifiableList(List) unmodifiable}. 2496 * 2497 * @see #getFormats(String) 2498 */ 2499 public static final List<String> FORMAT_DEFAULT = List.of("java.class", "java.properties"); I think you should also change the JavaDocs in the ResourceBundle.Control class for the constants FORMAT_CLASS, FORMAT_DEFAULT and FORMAT_PROPERTIES, because the JavaDocs for this constants explicitly mentions, that the lists are created by using Collections#unmodifiableList(List). Or you cannot change this constants at all because they are part of the Public API and existed in this form for a long time. Please ask someone from Oracle for help. They can explain it better when it is OK to change and when not. Maybe Stuart can do that. Best regards, Andrej Golovnin