In this tip we will see a simple command that will help you check whether Java is installed or not on Ubuntu 11.10/11.04. If you want to install Java on Ubuntu 11.10/11.04, check these two articles: Java 6 or Java 7.
Open now the terminal and run this command to check your current Java version (OpenJDK is also included):
Here is the output returned for my system:
# java -version
java version "1.6.0_23"
OpenJDK Runtime Environment (IcedTea6 1.11pre) (6b23~pre10-0ubuntu5)
OpenJDK Client VM (build 20.0-b11, mixed mode, sharing)