Java – Eclipse: No Java virtual machine was found after searching the following locations: /Library/Java/JavaVirtualMachines/jdk1.8.0_121.jdk/Contents/

Eclipse will by default try to launch with the default "java.exe" (the first one referenced by your PATH)

Three things to remember:

• "Installing" a JRE or a JDK can be as simple as unzipping or copying it from another computer: there is no special installation steps, and you can have as many different JVM versions (1.4, 5.0, 6.0...) as you want, "installed" (copied) almost anywhere on your disk.
• I would recommend to always run Eclipse with the lastest JRE possible (to benefit from the latest hotspot evolutions). You can:
  • Reference that exact JRE path in your eclipse.ini.
  • Copy any JRE of your in your <eclipse>/jre directory. In both cases, no PATH to update.
• The JVM you will reference within your Eclipse session is not always the one used for launching Eclipse because:
  • You only need a JRE to launch Eclipse, but once Eclipse launched, you should register a JDK for your projects (especially for Java sources and debugging purposes, also in theory for compilation but Eclipse has its own Java compiler) Note: You could register just a JRE within Eclipse because it is enough to run your program, but again a JDK will allow for more operations.
  • Even though the default registered Java in Eclipse is the one used to launch the session, you can want to register an older SDK (including a non-Sun one) in order to run/debug your programs with a JRE similar to the one which will actually be used in production.

June 2012, jmbertucci comments:

I'm running Windows 7 64-bit and I had the 32-bit JRE installed. I downloaded Eclipse 64-bit which looks for a 64-bit JRE. Because I didn't have the 64-bit JRE it threw the error, which makes sense.

I went to the Java manual install page (which was not as directly accessible as you'd like) and installed the 64-bit version. See "Java Downloads for All Operating Systems". That was all I needed.

April 2016: Steve Mayne adds in the comments:

I had to edit the eclipse.ini file to reference the correct Java path - Eclipse doesn't use the environment PATH at all when there is a value in eclipse.ini.

You can explicitly tell Eclipse where to find it. Open eclipse.ini and add the following lines to the top of the file:

-vm
/absolute/path/to/jre6/bin

Update: I just nailed down the root cause on my own Windows machine. The GlassFish installer complained with exactly the same error message and after digging in GlassFish forums, the cause was clear: a corrupt JRE install on a Windows machine. My JRE came along with the JDK and the Java 6 JDK installer didn't install the JRE properly somehow. A DLL file was missing in JDK's JRE installation. After I reinstalled the standalone JRE from http://java.com, overwriting the old one, the GlassFish installer continued and also Eclipse was able to start flawlessly without those two lines in eclipse.ini.