In what language is it better to write the backend of an online bank?

Question

Backend

I downloaded one application on my phone, found that they have their own payment systems. You put money on your account and spend it in the application itself, it became interesting. After reading about the application, I found out that at the beginning it was in php, then it was rewritten in java. And I asked myself: why Java? You look at vacancies in banks - also Java. Can someone please explain why Java is everywhere in finance? Is there more security or what? What if we do the same in Python? Thank you.

Answer 1

For each code (for each jar / war-nickname) - its own virtual environment is created: a virtual machine.
Processes are isolated from each other.
Thus, the security in the Java environment is higher than where processes can see each other by default.
Nothing prevents you from running code in any language in an isolated environment.
But the problem is how to create it correctly without losing the performance of the code and not allowing processes to climb where they are not allowed.
You can write in any language. (License, I hope, already received?! ;)

Answer 2

It's very simple:
Initially, large companies began to write everything in Java, since it was easier and more understandable to write in it than in C ++ and Perl. Over time, since everyone wrote large software in Java, things began to appear in the language and in the ecosystem itself that made it easier to write software of this level. People have become accustomed to writing such things in Java using certain features of the platform.
A simple example: The gauge of a train. In the countries of the USSR - one track. In Europe and the USA it's different. Why is that? Initially, for some reason, they decided so, and then the entire infrastructure, all the tracks, all the trains, all the staff, and so on, began to be made to this width. And if, let's say, Russia wants to change the width, then it will have to change absolutely everything, and these are gigantic costs - time, money.