Changing key in HashMap

[Ike]

I have a situation whereby I may have to change a key in a HashMap. Is there
a better way to do this than to obtain the object associated with that key,
put() a new entry in the HashMap with the old object and the new key, then
delete the old HashMap entry? TIA, Ike

 

[Robert Klemme]

I have a situation whereby I may have to change a key in a HashMap. Is there
a better way to do this than to obtain the object associated with that key,
put() a new entry in the HashMap with the old object and the new key, then
delete the old HashMap entry? TIA, Ike

You can do

V x = map.remove(oldKey);
map.put(newKey, x);

Note: you may have to change the code depending on whether you allow
null values in the map and / or you cannot be sure that oldKey actually
exists in the map.

Regards

robert

 

[Patricia Shanahan]

I have a situation whereby I may have to change a key in a HashMap. Is there
a better way to do this than to obtain the object associated with that key,
put() a new entry in the HashMap with the old object and the new key, then
delete the old HashMap entry? TIA, Ike

No, I don't think there is a better way to do it.

The change of key will probably cause a change in bucket, so even if
there were a method to do it, HashMap would have to remove the old
key-value pair from one bucket, and insert with the new key it its
appropriate bucket.

Patricia

 

[Mike Schilling]

I have a situation whereby I may have to change a key in a HashMap. Is
there a better way to do this than to obtain the object associated with
that key, put() a new entry in the HashMap with the old object and the new
key, then delete the old HashMap entry? TIA, Ike

Assuming that the change affects either equals() or hashCode(), then, no,
there's no better way. If the change doesn't affect either of those
methods, then there's no need to do anything.

 

[Adam Maass]

I have a situation whereby I may have to change a key in a HashMap. Is
there a better way to do this than to obtain the object associated with
that key, put() a new entry in the HashMap with the old object and the new
key, then delete the old HashMap entry? TIA, Ike

Well, other than a minor optimization, not really:


Map m...

void replace(Object oldKey, Object newKey){
m.put(newKey, m.remove(oldKey));
}

The 'remove' method returns the value, if any, associated with the key that
was removed.