Java - learn once, write anywhere
"From my personal experience, that is quite true. I started programming in Java in 1997, and since then I have built web applications, database applications, mobile applications for Palm and Pocket PC, an application server for CTI applications, CORBA-based distributed applications, network management applications, server-side business components for application servers, fat-client business applications, an IDE, a Rich Client Platform, a modeling tool among other kinds of software. All that across different operating systems and using similar products by different vendors.
Of course I had to learn something new for each kind of "application style", but the programming language and core class library were always there for me. That is a huge thing. Before Java, it was really hard to move from one domain to another, or even move from vendor to vendor. Sun has my eternal gratitude for bringing some sanity to the software development industry."
- Rafael Chavez