Summing values in hash table

[akerman]

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.

[Norm]

Have you looked at the API doc for the Map interface? It has several methods that can be used to get the contents of the Map. What have you tried?

[akerman]

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.

[Norm]

If you are having problems with your code, post the code and your questions.

[akerman]

.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

[Norm]

Sorry, I have no idea what that code is doing. Too many definitions are missing.

What language is that? Java does not have :: syntax

[akerman]

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)));

[Norm]

What language is that? The :: doesn't look like java.

[akerman]

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?

[Norm]

What makes something more efficient? Does it always give the correct answer?