title: Optimized implementations of java.util.Map and java.util.Set?
body: <p>I am writing an application where memory, and to a lesser extent speed, are vital. I have found from profiling that I spend a great deal of time in Map and Set operations. While I look at ways to call these methods less, I am wondering whether anyone out there has written, or come across, implementations that significantly improve on access time or memory overhead? or at least, that can improve these things given some assumptions? </p>
  
  <p>From looking at the JDK source I can't believe that it can't be made faster or leaner.</p>
  
  <p>I am aware of Commons Collections, but I don't believe it has any implementation whose goal is to be faster or leaner. Same for Google Collections.</p>
  
  <p>Update: Should have noted that I do not need thread safety.</p>