If you have Mac OS X Lion, Mountain Lion or Mavericks (version 10.7, 10.8, or 10.9 respectively) or anything newer, you need Java 6 to run MPLAB® X IDE. If you have encountered a Java 6 issue during the MPLAB X IDE installation, please follow these instructions if this applies to you:
Your computer doesn't have Java installed or has Java 7 installed, but not Java 6.
In this case, you need to download the update for Java 6 from Apple by visiting this Apple Knowledge Base article. The download button for Java 6 is in the upper right corner of the page.
Java 6 and 7 should be able to coexist on your machine, though Java 7 should be installed first. If you install Java 6 first, then Java 7, it will be treated as an upgrade and remove Java 6.
The default JVM used to run applications will continue to be Java 7 after the installation of Java 6. The MPLAB X IDE installer will find and use Java 6 once it is installed.
How to check your computer's Java version
If you're not sure what version of Java is installed on your computer, open a Terminal (Applications -> Utilities -> Terminal.app) and type this at the shell prompt:
This will report which default version you have installed on your computer. If Java is not installed, it will open a window with a message about Java missing. In that case, see above to install Java 6.
If you have more than one JVM installed on your machine, you can locate each of them by executing these commands:
/usr/libexec/java_home -v 1.6
/usr/libexec/java_home -v 1.7