我尝试在Ubuntu 12.04上安装Pycharm，并且得到以下信息：

user@user:~/Pobrane/pycharm-2.5.2/bin$ sh pycharm.sh
OpenJDK Runtime Environment (IcedTea6 1.11.1) (6b24-1.11.1-4ubuntu3)
OpenJDK Server VM (build 20.0-b12, mixed mode)
WARNING: You are launching the IDE using OpenJDK Java runtime.

         ITS KNOWN TO HAVE PERFORMANCE AND GRAPHICS ISSUES!
         SWITCH TO THE ORACLE(SUN) JDK BEFORE REPORTING PROBLEMS!

NOTE:    If you have both Oracle (Sun) JDK and OpenJDK installed
         please validate either PYCHARM_JDK, JDK_HOME, or JAVA_HOME environment variable points to valid Oracle (Sun) JDK installation.
         See http://ow.ly/6TuKQ for more info on switching default JDK.

Press Enter to continue.

正常工作该怎么办？