Map
key, a Set
element, or an array element in a sequence of
add
/put
calls or using a Java 9 factory method like Set.of
(which will result in runtime exception).
This usually occurs due to a copy-paste error.
Example:
map.put("A", 1);
map.put("B", 2);
map.put("C", 3);
map.put("D", 4);
map.put("A", 5); // duplicating key "A", overwrites the previously written entry
New in 2017.3