Maybe I'd pick when apple removed the default install from mac os, or maybe I'd pick when browsers made it impossible to run applets, or maybe I'd pick when the major java IDEs started pushing other languages like kotlin or xtend, or maybe I'd pick the oracle acquisition (never a good thing), or maybe I'd pick the release of go - a language squarely targetting pretty much the only niche that java has left (enterprise development of servers by mixed ability teams), maybe I'd pick the point when java development felt like it became more like configuring metadata for frameworks than actually coding, or maybe I'd pick when google started showing kotlin as the default language for developing on Android rather than Java.
Here's google trends for java: https://trends.google.com/trends/explore?date=all&geo=US&q=j...
Java-the-language is not going away any time soon, but if you expect it to do anything except decline, I think the future will be disappointing.