{"eventName":"event1","date":"date1"},
{"eventName":"event2","date":"date2"},
{"eventName":"event3","date":"date3"},
{"eventName":"event4","date":"date4"},
{"eventName":"event5","date":"date5"},
{"eventName":"event6","date":"date6"}

We have below 3 operations 
1. given a date , find number of events happened on that day
2. given two dates , find the number of events happened in that duration
3. given a eventName and date , find if the event happened on that date

what would be the efficient datastructure to hold this data( Java collection if any in specific) keeping the above operations in mind.
Please back your selection with explaination.