Get values for a key in multiple TreeMaps

Dear all,

I have a number of TreeMaps <Long, Integer> each containing values for a specific dataset.

Map<Long, Integer> Heating = new TreeMap<>();
Map <Long, Integer> Cooling = new TreeMap<>();
Map <Long, Integer> Appliances = new TreeMap<>();

I am now trying to write out the values to a file line by line.  

Usually I iterate through a map in the following way but not sure how to get each value for the same long (Date/TIme) into a string, i.e. Date key , Heating value, Cooling value, Appliances value.


Iterator<Map.Entry<Long, Integer>> entries = map.entrySet().iterator();
while (entries.hasNext()) {
    Map.Entry<Long, Integer> entry =;
    System.out.println("Key = " + entry.getKey() + ", Value = " + entry.getValue());

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mccarlIT Business Systems Analyst / Software DeveloperCommented:
Quick and Dirty solution...

Just access the other maps by the key that you are currently iterating, ie. if you are iterating over the Heating map, the Heating value is retrieved easily as entry.getValue(), the other values can be retrieved by Cooling.get(entry.getKey()) and Appliances.get(entry.getKey())

Recommended solution...

Refactor your code so that you have just one map and the values of the map are objects that contain all data that you need for that same long (Date/Time). ie. you might create a class called "Values" that simply hold one value for Heating, one for Cooling, one for Appliances (the specifics of this class, ie. whether it is immutable or not, etc will depend on how the data in these maps gets populated).

Then you can just have the one TreeMap, such as.... Map<Long, Values> map = new TreeMap<>();

Then when you iterate over that map, you cant print out, entry.getKey(), entry.getValue().getHeating(), entry.getValue().getCooling(), and entry.getValue().getAppliances()

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