I've experienced the following behavior on a Mac (newly updated to Mavericks):
1. Without any version of Java installed, I download the latest Eclipse, and try to launch Eclipse. I get a message (which I expect to get) asking me if I want to install Java.
2. I close the message and on my own, I visit java.oracle.com and download/install the JRE for Mac OS.
3. After installing the JRE, I try to launch Eclipse again, and again I get a message asking if I want to install Java. (This time, I'm somewhat surprised.)
4. I close the newest message and on my own, I visit java.oracle.com again and I download/install the JDK for Mac OS.
5. After installing the JDK, I successfully launch Eclipse without getting a message about Java.
6. "Self," I say, "this means that the Mac is checking for Oracle's JDK, and not for the plain old JRE when you try to launch Eclipse."
7. Later in the week I visit developers.android.com and I download the ADT Bundle which includes a customized version of Eclipse.
8. After installing the customized version of Eclipse, I try to launch the customized version and (with the JDK still installed) I get a message asking me if I want to install Java. When I dismiss the message, Eclipse fails to launch. (And at this point I'm really confused.)
9. I try to launch the customized Eclipse again, and this time I accept the suggestion to install Java, which it does. (This is Apple's Java 6, I thing.)
10. After following the suggestion to install Java, the customized Eclipse runs.
I know how to check for /Libraries/Java ... and /System/Libraries/Java ... and I don't think I'm missing any details about which versions of Java are, or are not, installed. Can anyone explain this behavior to me?