Java was conceptualized back in 1991, but it was too advanced for its original purpose of helping broadcast cable news better. Finally, in 1995, first public release of Java 1.0 was made by Sun Microsystems.
This language has been around a long time, and is known for its battle-hardened reliability. The JVM lets you write platform independent Java code. This is achieved by first compiling the source code to bytecode, which is later translated to corresponding machine code. The big advantage of this procedure is that bytecode runs inside the JVM, which is responsible for compiling it into matching machine code during runtime. Oracle ensures that your code remains platform independent, by providing you different implementations of JVM for different platforms (Windows, Mac, Linux etc.). Ultimately the JVM interfaces communicate with the low-level system APIs.
Java is massively used in enterprise applications, Android application development, small embedded systems and myriad of other places. It can also be used on a webserver for backend development.
Its huge popularity and large number of libraries have helped it grow into a mature, dependant platform.