how to merge the list of values to the same Key in hashmap?

Question

how to merge the list of values to the same Key in hashmap?
if I use the above logic I'm getting below result as an output {Adam=[[Subject, ComputerScience], [Subject, ComputerScience]]}

But I have to merge like the below result, is it possible to append the list of values to the same key?

{Adam=[Subject, ComputerScience,Subject, ComputerScience]}

    public class DemoMap {
        
        public static void main(String[] args) {
            
            HashMap<String, ArrayList<String>> tmeMap = new HashMap<>();
            HashMap<String, ArrayList<Object>> mngrMap = new HashMap<>();
            ArrayList<Object> emailcontent = new ArrayList<>();
             ArrayList<String> mngrList1 = new ArrayList<>();
             mngrList1.add("Jay");
             mngrList1.add("Aaron");
             tmeMap.put("Adam", mngrList1);
        
     //Adam is Senior Manager who has the list of managers under him
 
            emailcontent.add("Subject");
            emailcontent.add("ComputerScience");
            
            mngrMap.put("Jay", emailcontent);
            mngrMap.put("Aaron", emailcontent);

   //Each manager will have the email content       

            ArrayList<Object> collectionOfManagerContent = new ArrayList<>();
            for (Map.Entry<String,ArrayList<Object>> emailEntry : mngrMap.entrySet()) {
                collectionOfManagerContent.add(emailEntry.getValue());
            }

   //our Target is to show the manager's content to Senior Project manager      

            HashMap<String, ArrayList<Object>> tmeEmailMap1 = new HashMap<>();
            for (Map.Entry<String,ArrayList<String>> emailEntry : tmeMap.entrySet()) {
                emailEntry.getValue();
                tmeEmailMap1.put(emailEntry.getKey(), collectionOfManagerContent);
            }
            System.out.println(tmeEmailMap1.toString());
            
        }
    
    }

Answer 1

Use addAll() to add all elements of ArrayList into another ArrayList

for (Map.Entry<String,ArrayList<Object>> emailEntry : mngrMap.entrySet()) {
    collectionOfManagerContent.addAll(emailEntry.getValue());
}