The code is compiled so it is not possible to view the source code. You can set the compilation mode to Release (Obfuscated) to make it more difficult to reverse engineer it.
anything compiled for android can be reversed back into real source code using free online tools, as its a runtime based environment.
However, obfuscation does make it harder to figure out what is what. But any hacker/programmer that is skilled in the language can figure out how things work.
Even C# .NET programs can be reversed back into source code as well.
1. Reverse engineering is not special to B4A. This is exactly the same as with Java / Kotlin written apps.
2. If you compile with obfuscation then it will be more difficult to reverse engineer the code.
Theoretically it is possible to use resources and code from compiled apps.