If Java is not installed when you run the Windows Ptolemy II installer, then you will be directed to install a Java Runtime Environment (JRE). This JRE is separate from the JRE that is included in the Windows Ptolemy II installer. Which Installer? Under Windows, the Ptolemy II installer includes a private copy of the Java Runtime Environment (JRE). The private copy of the JRE includes Java packages that are used by various domains and actors.