#traverse all the directory and subdirectory
define walk
$(wildcard $(1)) $(foreach e, $(wildcard $(1)/*), $(call walk, $(e)))
endef
#traverse Classes Directory
ALLFILES = $(call walk, $(LOCAL_PATH)/../../Classes)
FILE_LIST := hellocpp/main.cpp
FILE_LIST += $(filter %.cpp, $(ALLFILES))
FILE_INCLUDES := $(shell find $(LOCAL_PATH)/../../Classes -type d)
#source file will be compiled
LOCAL_SRC_FILES := $(FILE_LIST:$(LOCAL_PATH)/%=%)