Finding number of values in a HashMap?

If I understand the question correctly, you have a Map<String, List<Something>>, and you want to count the total number of items in all the Lists in the Map's values. Java 8 offers a pretty easy way of doing this by streaming the values, mapping them to their size() and then just summing them:

Map<String, List<Something>> map = ...;
int totalSize = map.values().stream().mapToInt(List::size).sum());

Easiest would be, iterate and add over list sizes.

int total = 0;
for (List<Foo> l : map.values()) {
    total += l.size();
}

// here is the total values size

Say you have a map

Map<String, List<Object>> map = new HashMap<>();

You can do this by calling the values() method and calling size() method for all the lists:

int total = 0;
Collection<List<Object>> listOfValues = map.values();
for (List<Object> oneList : listOfValues) {
    total += oneList.size();
}

In Java 8, you can also utilize the Stream API:

int total = map.values()
               .stream()
               .mapToInt(List::size) // or (l -> l.size())
               .sum()

This has the advantage that you don't have to repeat the List<Foo> type for a for variable, as in the pre-Java 8 solution:

int total = 0;
for (List<Foo> list : map.values())
{
    total += list.size();
}
System.out.println(total);

In addition to that, although not advised, you could also use that value inline without needing a temp variable:

System.out.println(map.values().stream().mapToInt(List::size).sum());