Code Tools: jmh

JMH is a Java harness for building, running, and analysing nano/micro/milli/macro benchmarks written in Java and other languages targetting the JVM.

http://openjdk.java.net/projects/code-tools/jmh/

How to figure out where is java installed on MacOs

Use /usr/libexec/java_home -v 1.x command on a terminal shell to figure out where is your java 1.x home directory

Invoke dynamic in java 7

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

Compressed oops in the Hotspot JVM 7 - new optimization

What is Compressed oops in the Hotspot JVM? It's a pointer to an object. They are stored in the Java heap. Not all of them are pointers to objects, but also e.g. pointers to fields in objects. Before Java 6u23 pointers have size corresponding with platform (32 bites or 64 bites) by default.
So unfortunately, on a 64 bites platform, applications need bigger heap.

In Java 7 by default, for heap smaller than 32GB, pointers are saved as 32 bites offset from the address of heap beginning. For bigger heaps pointers are addressed with 64 bites.