Is it possible to rename a Hashmap key?

Question

I'm looking for a way to rename a Hashmap key, but i don't know if it's possible in Java.

Answer 1

Try to remove the element and put it again with the new name. Assuming the keys in your map are String, it could be achieved that way:

Object obj = map.remove("oldKey");
map.put("newKey", obj);

Answer 2

hashMap.put("New_Key", hashMap.remove("Old_Key"));

This will do what you want but, you will notice that the location of the key has changed.

Answer 3

Assign the value of the key, which need to be renamed, to an new key. And remove the old key.

hashMap.put("New_Key", hashMap.get("Old_Key"));
hashMap.remove("Old_Key");

Answer 4

You cannot rename/modify the hashmap key once added.

Only way is to delete/remove the key and insert with new key and value pair.

Reason : In hashmap internal implementation the Hashmap key modifier marked as final.

static class Entry<K ,V> implements Map.Entry<K ,V>
{
    final K key;
    V value;
    Entry<K ,V> next;
    final int hash;
    ...//More code goes here
}

For Reference : HashMap

Answer 5

You don't rename a hashmap key, you have to insert a new entry with the new key and delete the old one.

Answer 6

I'd argue the essence of hasmap keys are for index access purposes and nothing more but here's a hack: making a key-wrapper class around the value of the key so the key-wrapper object becomes the hashmap key for index access, so you may access and change key-wrapper object's value for your specific needs:

public class KeyWrapper<T>{

      private T key;
      public KeyWrapper(T key){
         this.key=key;
       }

      public void rename(T newkey){
              this.key=newkey;
       }

}

Example

   HashMap<KeyWrapper,String> hashmap=new HashMap<>();
   KeyWrapper key=new KeyWrapper("cool-key");
   hashmap.put(key,"value");
   key.rename("cool-key-renamed");

Though you could also have a non existing key be able to get the value of an existing key from the hashmap but I fear it might be criminal, anyways:

public  class KeyWrapper<T>{

        private T key;
        public KeyWrapper(T key){
            this.key=key;
        }

        @Override
        public boolean equals(Object o) {
            return hashCode()==o.hashCode();
        }

        @Override
        public int hashCode() {
            int hash=((String)key).length();//however you want your hash to be computed such that two different objects may share the same at some point
            return hash;
        }
    }

Example

HashMap<KeyWrapper,String> hashmap=new HashMap<>();
KeyWrapper cool_key=new KeyWrapper("cool-key");
KeyWrapper fake_key=new KeyWrapper("fake-key");
hashmap.put(cool_key,"cool-value");
System.out.println("I don't believe it but its: "+hashmap.containsKey(fake_key)+" OMG!!!");

Answer 7

In my case had a map containing not real key -> real keys, so I had to replace the not reals with the reals in my map (the idea is like others)

getFriendlyFieldsMapping().forEach((friendlyKey, realKey) ->
    if (map.containsKey(friendlyKey))
        map.put(realKey, map.remove(friendlyKey))
);

Answer 8

Please look below points:

1. No,You can not rename the key of HashMap once added.

2. Very first you have to delete or remove that key and then you can insert with new key with value.

3. Because in HashMap internal implementation the HashMap key modifier is final.

Answer 9

You can, if instead of Java native HashMap you'll use a Bimap.
It's not the traditional Map implementation, and you need to make sure it's suits your needs.

A bimap (or "bidirectional map") is a map that preserves the uniqueness of its values as well as that of its keys. This constraint enables bimaps to support an "inverse view", which is another bimap containing the same entries as this bimap but with reversed keys and values.

Using a bimap, you can inverse the view and replace the key.
Checkout both Apache Commons BidiMap and Guava BiMap.