YOU MAY NOT KNOW... (ECLIPSE QUICKTIP)

...That Eclipse's "Open With" pop-up context option is a persistent setting for the selected file. In other words, if you open a specific java source file with an alternate editor by selecting that editor in the "Open With" pop up, Eclipse remembers that decision for that file and will use the selected editor to open that file when it is double clicked on from then on. You need to use the contextual pop-up to reset your choice if you want to open that file in Eclipse again by default when its double clicked. That feature bedeviled me for two days until I realized that your previous selection is subtly highlighted in the pop-up -indicating its persistence.