I try to install Pycharm on Ubuntu 12.04 and I have this information:
user@user:~/Pobrane/pycharm-2.5.2/bin$ sh pycharm.sh
OpenJDK Runtime Environment (IcedTea6
The Oracle (Sun) JDK is no longer included by most newer distributions due to restrictions set by Oracle. Instead they ship with OpenSDK. While OpenSDK works for most applications, PyCharm seems to have some issues with it.
You have to install the Oracle (Sun) JDK manually and make sure it's the default JDK or set the appropriate environment variables when launching PyCharm.