Dynamically adding multiple values to a key in JAVA

Question

I have multiple records received as string through a query. I want to store records having the same "long" key in a collection dynamically as I parse them in a loop. Like, insert key and value and if the key exists, it adds to the values and if not, a new key is created. What would be the most efficient way of doing this? I can do it using multiple arrays but I would prefer a cleaner way.

I cannot use a HashMap as I have to first store the records in an Array or ArrayList and then insert it which defeats the purpose as I have to group the lists by key first anyway. The no. of records will not more than 50 at a time.

E.g data:

for(i = 0; i < numRecords; i++ ) {  
    Data: 1 "A", 2 "B", 1 "C", 3 "D", 1 "E"   
}

I want to have a collection where inside the loop I can just add: 1 "A" and so on..

Subhrajyoti Majumder · Accepted Answer · 2012-12-05 16:46:05Z

4

I think Map<Long,List<String>> may help you.

Map<Long,List<String>> map = new HashMap<>();
...
if(map.get(key)!=null){
  List<String> list = map.get(key);
  list.add(value);
}else{
  List<String> list = new ArrayList<>();
  list.add(value);
  map.put(key,list);
}

answered Dec 5, 2012 at 16:46

Subhrajyoti Majumder

41.3k13 gold badges84 silver badges103 bronze badges

Sign up to request clarification or add additional context in comments.

5 Comments

Rachit Over a year ago

Why do I get this error: '<>' operator is not allowed for source level below 1.7 for both the new HashMap and ArrayList declaration. I want to use only Java 1.6

vishal_aim Over a year ago

then use new HashMap<Long,List<String>>() as empty <> are not supported for java 1.6

Rachit Over a year ago

Yes this suits my purpose ver well. Thank you very much!

Rachit Over a year ago

One more question, how efficient would be using this and then iterating again in the next segment to get the values for so few records? And can I have multiple values to one key? e.g. Long key has List<String> and List<int> as values?

Rachit Over a year ago

Got it. Just created a class with values as members and gave the class object as List type. Thanks a lot for your help!

Collectives™ on Stack Overflow

Dynamically adding multiple values to a key in JAVA

1 Answer 1

5 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

5 Comments

Your Answer

Sign up or log in

Post as a guest

Related