To decompile any Android (Java) program is very simple.
B4A offers to compile in obfuscated mode. This can discourage to "import" the pieces of code, but is not able to crypt a communication.
For example, a hacker can find httpJob object and where you read data, something like
_stringresponse = _httpjobinstance._vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv4 /*String*/ ().trim();
Then he will search, what you do with _stringresponse.
IMO, it's not possible to keep secrets in Android. But typically it's not needed. Depends, what exactly do you want to prevent