Thread: Summing values in hash table

Hi there;

Just a simple question which has caused me problems.

I created hashtable:

private  Map <String, Double> v = new ConcurrentHashMap<String, Double>();

In one of my method I would like to sum all the number which are doubles and display it as system.out.print.... Not sure how to get the sum just from the second field for each existing pair.

I have seen a loop what it firstly takes the size and then calculates the sum. But I know there is an easier way using for loop... but could find an example which would help me.

.collect(Collectors.groupingBy(Employee::getDepartment,
Collectors.summingInt(Employee::getSalary)));

I was trying to use above example get the sum but I was not able to adapt it so it would work with my map

Well this is the example I found which might be useful but I wasn't able to adapt it:

// Compute sum of salaries by department
Map<Department, Integer> totalByDept = employees.stream()
.collect(Collectors.groupingBy(Employee::getDepartment,
Collectors.summingInt(Employee::getSalary)));

I found it in the map api for java... neverless I decided to use this function:

double total = 0;
    	for (Double value : voltages.values()) {
    	    total = total + value;

Is there a better way or more efficient?