Recently I have attended Confitura 2012 a Java Conference in Warsaw. One of the most interesting lectures was the one made by Waldemar Kot. He has introduced subject of the new instruction in Java 7: Invoke dynamic.
He has shown that it has a very big impact on the java development, not only on dynamic languages on JVM. Using invoke dynamic in java you can have dynamic behavior with speed comparable to static invocation.
You can see examples and benchmarks here: https://github.com/waldekkot/Confitura2012_InvokeDynamic