static public Value put( Key key, Value val ) {
    Futures fs = new Futures();
    Value old = put(key,val,fs);
    fs.blockForPending();
    return old;
  }
static public Value put ( Key key , Value val ) { Futures fs = new Futures ( ) ; Value old = put ( key , val , fs ) ; fs . blockForPending ( ) ; return old ; }
Make the mapping <em>key -&gt; val</em>.  Blocking, caching.