At first it does not harm anything directly. But ...

Your concern makes sense. If the application has problems it can at least leave the device vulnerable if it can somehow be accessed externally directly or more rarely indirectly.

Note that this risk is not so great. And in general applications can not do as much damage as possible on a computer with more freedom of action for applications. Nothing can access the application so easily. And as far as I know the vast majority of applications developed little exposes arbitrary external access.

So it's good to know that there are no guarantees but you do not have to worry too much that any wrong thing that is done will be a big problem. In general, more advanced technologies will give you more chances for vulnerabilities. If you are going to use more advanced things, of course you need to master its use. Normally I would say that the domain is needed to do anything in software, but I have already seen that the current trend is for everyone to go out doing what they do not know without a lot of worry about risks.

Of course, some care needs to be taken. You have to keep a close eye on the entire application cycle while it is in testing.

I will not even try to say that there are application monitoring techniques to understand everything that is happening to it. This in itself is already an advanced technique.

I imagine you're going to use Java to develop. This is a language that helps you not to make a lot of mistakes and leave the application vulnerable in many ways. But it's no miracle, if you do not use proper techniques it can compromise your safety.

But know that the applications for this platform are usually active, meaning they take the action out. Rarely do they let external source take actions. So that helps a lot. Of course you can accidentally release external access. But it is very difficult to do this. It is often difficult to do this by wanting to, unintentionally imagining.

Conclusion

• The risk exists but it is small, usually very small.
• Pay attention, study to understand what you are doing.
• Do not let the application test run without a monitoring until you have confidence that nothing is wrong.
• Avoid using what you do not know enough and ask for help when you need it.
• Knowing that there are minimal risks, ensure that there are no critical data that can not be lost, such as passwords for accessing internal or external resources.