在TreeMap中删除地图元素

Question

I have this structure

TreeMap<String,Map<String,String>> map;

And i want to remove one of the key-value pair inside the Map found by a key. I tried:

map.get(key).remove(key2);

But it throws a NullPointerException. To find the problem i tried:

Map<String,String> aux = map.get(key);
aux.remove(key2);

and saw that the map.get just returns null.

Any solution? Thank you in advance!

Answer 1

You could check if the outer key (in this case key ) is present in the outer map and invoke the second get only if that is true.

Map<String,String> outerKey = map.get(key);
if(outerKey != null) {
    outerKey.remove(key2)
}

You get the NullPointerException because the key key is not present in the outer map (or is mapped to a null value), so map.get(key) returns null.