title: Enhance library for Java 8 while keeping backwards compatibility
body: <p>I'm developing an open source library in Java and would like to ensure that it is convenient for Java 8 users, and takes advantage of new concepts in Java 8 wherever possible (lambdas etc.)</p>
  
  <p>At the same time I absolutely need to maintain backwards compatibility (the library must still be usable for people using Java 6 or 7).</p>
  
  <p>What useful features from Java 8 can I adopt that would be beneficial for library users without breaking library compatibility for users of older Java versions?</p>