It's a Android app example in SDK, to implement SoftKeyboard. It should be in in your Android SDK directory:
If you import in Android SDK-Eclipse, may be you have to manually set your target SDK:
Right click your project -> Properties -> Select Android on the left, and check Project Build Target of Android 5.1.
Otherwise, error of No resource identifier found for attribute 'supportsSwitchingToNextInputMethod' will be reported in method.xml.
To know more about An input method editor (IME), visit: Creating an Input Method