I'm working on a java eclipse RCP project where Package explorer shows 4 packages and three of them having a META-INF folder and each of them contains a MANIFEST.MF file.
and each package (except one) has its own build.properties.
I don't understand why there three META-INF folders.
I also couldn't determine how these packages interact themselves because the classes withing a package have no reference on other packages.
Any tips to understand this structure will be helpful. Thank you.
It sounds like you have an RCP set up using nested projects. This is sometimes recommended to help organize RCP projects. Each of the 'packages' is actually a separate project. Project Explorer displays the projects hierarchically when that is selected as the project presentation style.
As an example here is one of my RCPs:
Note: in this example I have told Project Explorer to show all the .project and .classpath files which are normally hidden. This helps to show which folders are projects.
It has a top level project ('greg.music') containing a number of folders (.mvn, bundles, features, releng...). The 'bundles' folder contains two plug-in projects (greg.music.e4.rcp, greg.synch.jsynchfiles).
This particular structure is common for projects using maven and Eclipse tycho