Is there a Map implementation in Java that will use case-insensitive String matching for the key, but also supports the null key? I know that
new TreeMap<String, String>(String.CASE_INSENSITIVE_ORDER)
supports case-insensitive matching of String keys, but it doesn't support the null key.
If you're on Java 8, the following will create a null-compatible, case-insensitive TreeMap:
Comparator<String> cmp = Comparator.nullsFirst(String.CASE_INSENSITIVE_ORDER);
TreeMap<String, String> map = new TreeMap<>(cmp);
No external libraries needed.
get, put and remove operations will be O(log(n))You can use CaseInsensitiveMap for this. This will fulfill your requirement. It is case-insensitive as well as supports null keys.
From the doc
A case-insensitive Map. Before keys are added to the map or compared to other existing keys, they are converted to all lowercase in a locale-independent fashion by using information from the Unicode data file.
Null keys are supported.
The keySet() method returns all lowercase keys, or nulls.
If you would prefer not using external libraries, you could make your own wrapper for String.CASE_INSENSITIVE_ORDER that sorts nulls in a predictable way:
NavigableMap<String,String> m = new TreeMap(
new Comparator<String>() {
public int compare(String s1, String s2) {
if (s1 == null && s2 == null) return 0;
if (s1 != null && s2 != null) {
return String.CASE_INSENSITIVE_ORDER.compare(s1, s2);
}
return s1 == null ? -1 : 1;
}
}
);
equalsandhashCodeso that they work case insensitive.Objects.toString(key)when inserting in the map. That will map the key to the stringnull.