Resource IDs and R.java

Every resource file gets an ID assigned by the Android build system. The gen directory in an Android project contains the R.java references file which contains these generated values. These references are static integer values.

If you add a new resource file, the corresponding reference is automatically created in R.java file. Manual changes in the R.java file are not necessary and are overridden by the tooling.

The Android system provides methods to access the corresponding resource files via these IDs.

For example to access a String with the R.string.yourString ID in your source code, you would use the getString(R.string.yourString)) method.