title: Fastest data structure for contains() in Java?
body: <p>What's the data structure in Java that has the fastest operation for contains() ?</p>
  
  <p>e.g. i have a set of numbers { 1, 7, 12, 14, 20... }</p>
  
  <p>Given another arbitrary number x, what's the fastest way (on average) to generate the boolean value of whether x is contained in the set or not? The probability for !contains() is about 5x higher.</p>
  
  <p>Do all the map structures provide o(1) operation? Is HashSet the fastest way to go?</p>