Adding values under same key HashMap in Java

April 27, 2022

I’m new to HashMaps, and I was wondering if there was a way to add values together if they have the same key.

For example, when I have the key ‘a’ and the value is 20 and later on I use the key ‘a’ again and the value is 10 the value should now be 30.

I don’t know how I would check if the Value already is in the HashMap and then use the same value again. The adding part could be done with just a variable that copies the current value and adds the new one, I guess.

Thank you guys in advance.

>Solution :

I am guessing you want a hashmap for character vs integer and want to add the integer to already present value in case the value is present.You can do something like below:

public hashMapImpl(char ch, int number){
    Map<Character,Integer> map = new HashMap<>();
    if(map.containsKey(ch)){
        map.put(ch, map.get(ch)+number);
    }
    else{
        map.put(ch,number);
    }
}

Where ch will be your key and number will be something that you want to store at particular key.