Mac OS X 10.7 (Lion) has only Java 1.6 and later, so there is nothing further to be done.
To determine which version of the operating system is running, click on the apple icon in the upper left and select "About this Mac".
If you are running "Mac OS X 10.7" or later, then go to the next step.
If you are running Mac OS 10.6 or earlier, then read on and verify that Java 1.6 is the default version.
See Ptolemy II Installation for details, but briefly:
Ptolemy II requires Java 1.6 because ptdb uses javax.swing.GroupLayout. Also, Java 1.5 is past its end of life.
To determine which version of Java is being run, start up a Terminal window by going to Application -> Utilities and clicking on the Terminal icon.
Then type:
java -version
If you are running Java 1.6 or later, then go to the next step.
If you are running Java 1.5, then you are probably using Mac OS 10.5. We recommend using the 32-bit version of Java, which is handled in the next step.