问题
I initially thought it was exclusively for official libraries like the support library. However any time I add a custom JAR using the "Add to build path" menu item, it automatically shows up in both "Referenced Libraries" and "Android Private Libraries". One of these is redundant since there is no point in exporting both at build time. Additionally, "Android Private Libraries" cannot be modified so I can't (easily) add java doc or source paths. Not to mention it just seems wrong that a custom JAR is in "Android Private Libraries".
I cannot delete the entry from "Android Private Libraries" to use only "Referenced Libraries" either.
回答1:
In my case i always add libraries to libs folder.
According to my understanding thats the way its suppose to be. Android Private Library folder references these jars in libs folder. The Android Private Library is used during the creation of apk (probably during the conversion of your java code into dex file).
回答2:
I don't have any problem with custom jars. They are only in Reference Libraries in my case. I suggest you to look at Order and Export tab in java build path properties.Just check all the custom jars and uncheck all the Android specific libraries. If you want all jars in Reference Libraries then check all jars and clean your project.
回答3:
you just need to put jar and jardoc to a folder but not the folder "libs". Then there will be a 'Reference Library', Then you can add jardoc to jar by properties of jar in Reference Library.
1: New a Folder named sth but not "libs" like folder named 'lib'. 2: Put your .jar and .jardoc in the new folder the folder 'lib' in this tutorial 3: Add the jar and jardoc to project. Then, a 'Reference Libraries' will appear 4: Delete original jar/jardoc.jar in libs (if you've imported them to libs before). 5: add XXXjavadoc.jar to XXX.jar as doc location.
来源：https://stackoverflow.com/questions/20604193/what-is-the-android-private-libraries-folder-in-eclipse