Jaroslav Tulach is the founder and initial architect of NetBeans, which is not just a well known IDE, but also the first modular desktop application framework written in Java. Jaroslav has seen, made and helped to recover from many API design mistakes. Such experience obligated Jaroslav to sit down and write "Practical API Design" book. These days Jaroslav is helping OracleLabs to design API of Truffle which (together with GraalVM) is the fastest (Java) virtual machine on the planet.