I have installed both OpenJDK 6 and 7. When I run "java somefile" from the command line, OpenJDK 6 is invoked. I do not want to change this default behavior. What command can I use to run my non-default OpenJDK 7 installation instead? (I am used to running "python somefile" to invoke the default Python, "python2.7 somefile" to use Python 2.7 specifically and "python3 somefile" to use Python 3 specifically.)