just tried on API 23/24 and can just instance it.
these external*
properties might refer to the SD card.
PackageStats stats = new PackageStats(context.getPackageName());
long codeSize = stats.codeSize + stats.externalCodeSize;
long dataSize = stats.dataSize + stats.externalDataSize;
long cacheSize = stats.cacheSize + stats.externalCacheSize;
long appSize = codeSize + dataSize + cacheSize;