HashMap size() of multiple values that have the same key

Question

I created a hashMap of flights, the keys are the city names, which in this case one key could have multiple flight values. public HashMap<String,List> flights;

I added 20 pairs of key-value data into the map, but the size() method only returns 10 which is the number of keys. But when I print the information using a nested for loop, I could get all the flight info. I am wondering what is the output of the size() method of HashMap(). How would I get the size of the key-value pairs 20 in this case?

Answer 1

You can use Map#values and then sum all the sizes.

int size = map.values().stream().mapToInt(List::size).sum();