Eclipse Indigo is 3.7, and Eclipse Juno is 4.2, but 3.8M1 has just been released. What's 3.8 and how is this different from 3.7? I'm eagerly awaiting Java 7 support and am confused whether I should use 3.8M1 or wait for 3.7.1
...the feature and API set for the next feature release of the Eclipse SDK after 3.7, designated release 4.2 and code-named Juno. This release is occurring simultaneously with the 3.8 platform release. The 4.2 release is a mature platform release containing significant new feature work, while the 3.8 release focuses on stability and bug fixes.
From: http://www.eclipse.org/projects/project-plan.php?projectid=eclipse
Also, Java 7 support began with 3.7.1:
The Juno simultaneous release included both the 4.2 and the 3.8 versions of the Eclipse Application Platform (confusing, but true).
The 4.2 Eclipse Application Platform (also known as the e4, E4AP, or Eclipse 4.2 SDK) add changes to the workbench including "modeled UI, dependency injection and service-based programming model, CSS-based styling". Importantly, it also includes a 3.X compatibility layer. See the FAQ for more info.
Because of the compatibility layer, all of the Juno packages are supposed to run on either. The Juno packaged installs, however, are bundled with just the 4.2 Eclipse Application Platform.
That said, you can download the 3.8 Eclipse Platform and then install the Juno packages you want. See Eclipse 3.8: where is the download site? and How do I install an Eclipse EPP (for example EPP Modeling Feature on 3.8)?.
It's probably worth noting that 4.2 has numerous performance complaints (see What is the main reason for upgrading to Eclipse Juno? and Very slow Eclipse 4.2, how to make it more responsive?). This is probably related to the fact that the Eclipse Foundation ran out of funds to do the same performance testing on Juno that they have done in the past (see http://www.zdnet.com/google-sets-perfect-example-with-20000-donation-to-eclipse-7000003968/).
3.8M1 comes with Java 7 support. The JDT core build notes confirm that the work done for Java 7 support has been merged.
There is very important difference: the debug buttons are available on the main toolbar so that you can continue the execution with editor maximized. This is 4.2 feature, not available in 3.7
All plugins for 3.8 fit 4.2 and 4.3 e.g. R statet plugin for 3.8 can be installed together with ADT (Android) and Pydev after many years of incompatibility between 3.7 and 4.1 (and earlier version pairs). 3.8 is emulated by 4.2 or sth like that.
来源：https://stackoverflow.com/questions/6997190/what-the-difference-between-eclipse-3-7-3-8-and-4-2