Finding all keys in a HashMap with a character an replace it

Question

I have a HashMap and now i need to find all the keys inside the HashMap which has a particular letter inside it and replace it with another letter

Answer 1

You could try this :

public void replaceKeysChar(char originalChar, char newChar, Map<String, ?> map) {
    Map<String, Object> tempMap = new HashMap<String, Object>();
    for (Map.Entry<String, ?> entry : map.entrySet()) {
        String key = entry.getKey();
        if(key != null){
            key = key.replace(originalChar, newChar);
        }
        tempMap.put(key, entry.getValue());
    }
    map.clear();
    map.putAll(tempMap);
}

This way you handle only char, and you don't change the implementation. Plus when you iterate you don't add item in your map (it would be a bad idea).

If you don't care about the implementation simply return the tempMap and remove the clear/putAll part (it will consume less resources).

EDIT :

After @locka's answer I think I should specify that this method can't handle collisions.

If your Map contains the keys "toto" and "tata" and you do a `replaceKeysChar('a','o', map) only one of the values between "toto"'s value and "tata"'s value will be in the map, the other will simply be ignored.

EDIT bis:

To handle collisions with exceptions (à la @Stephen C) just replace the old for by this one :

    for (Map.Entry<String, ?> entry : map.entrySet()) {
        String key = entry.getKey();
        if(key != null){
            key = key.replace(originalChar, newChar);
        }
        if(tempMap.containsKey(key))
            throw new CollisionException();
        tempMap.put(key, entry.getValue());
    }

Answer 2

Here's a solution that "deals with" collisions by throwing an exception.

public void replaceKeysChar(char originalChar, char newChar, Map<String, ?> map) {
    Map<String, Object> tempMap = new HashMap<String, Object>();
    Set<String> tempSet = new HashSet<String>();
    for (Map.Entry<String, ?> entry : map.entrySet()) {
        String originalKey = entry.getKey();
        String newKey = originalKey .replace(originalChar, newChar);
        if (!newKey.equals(originalKey)) {
            if (map.containsKey(newKey) || tempMap.containsKey(newKey)) {
                throw new CollisionException(newKey);
            }
            tempMap.put(newKey, entry.getValue());
            tempSet.add(originalKey());
        }
    }
    map.keySet().removeAll(tempSet);
    map.putAll(tempMap);
}

EDIT

Fixed bugs ... in previous versions.