Why Java platform is preferred over PHP on financial applications?

If you want to build a start-up or web application you should probably go for Php. If you want to build a banking application or a fast performing computation engine - go for java, take a look to understand the importance of Java.

• Build systems with transparent failover (if part of hardware or software fails whole system is still going like nothing happens)
• Build software that guarantees success, ensure atomicity of complex operations (eg in banking, transaction with either be fully successful either not happening at all) via enterprise messaging, distributed transactions and more
• Java has good support for concurrency (at small and at big scale), which can be required by financial or computation engines
• Java JVM is still one of the fastest Virtual machines in the world and some things are just super fast with it (example - parsing is faster with java then with C++)
• This all comes with more complex technologies and therefore higher cost of building the system (more of more expensive developers)