Is it possible to write Android app without an SDK?

Just wondering, since Android apps are Java programs, would it be possible to write one entirely from scratch without using an SDK? If no, then why not开发者_StackOverflow社区?

No. Android apps are coded in Java- but only a subset of the standard Java API is included, and even that has a few custom modifications. Whilst the first stage of compiliation to a .apk file is to compile to Java bytecode, Android then has to convert that into Dalvik bytecode and package, sign, and zip align your application to make it run. In addition the SDK will handle generating necessary files like R.java and your xml that the ordinary Java compilers won't know how to handle.

So whilst you can easily code your entire project just using notepad, compilation will need the Android SDK.

You couldn't do it as you need the Android-specific classes that are part of the SDK. Not to mention the useful tools for creating the package (packing, signing, etc.) and other odds and sods.