Return a set of values from a map

Question

I have a map HashMap <Integer,Employee> map= new HashMap<Integer,Employee>(); The class Employee has an int attribute int empid; which will serve as key to the map.

My method is

public Set<Employee> listAllEmployees()
{
      return map.values();                //This returns a collection,I need a set
}

How to get set of employees from this method?

Solution 1

Just create a new HashSet with map.values()

public Set<Employee> listAllEmployees()
{
      return  new HashSet<Employee>(map.values());                
}

Solution 2

In Java 8 by Stream API you can use this method

public Set<Employee> listAllEmployees(Map<Integer,Employee> map){
    return map.entrySet().stream()
        .flatMap(e -> e.getValue().stream())
        .collect(Collectors.toSet());
}

Upd.: This code performs the task but is some kind of overcoding. Just KISS and do it as in answer here https://stackoverflow.com/a/19075053/4609353

Solution 3

Some other options.

You can still use the Collection Interface to do all possible set operations. Iteration, clear etc etc. (Note that the Collection returned by values() is an unmodifiable collection)

Use map.values().toArray() method and return an array.