what would be the differences between PHP and Java?

There must be hundreds of differences between these two languages. But I'd say the key differences are:

* Java is principly an object orientated programming language, where as PHP is principly a imperative scripting language (but does now support object orientation.)
* Java is portable and only requires the system intended to run an applictation has the Java Platform running on it - making it arcitecture neutral. PHP can be deployed on many systems, but does not use a VM environment like Java and is therefore less portable.
* PHPs intended purpose is to be a general-scripting langauge for web development (this is what you'll find almost all PHP applications doing). Java is a general purpose higher level programming language intended for many different purposes, something that you'll notice in the variety of packages that Java provides.

On the matter of security, read this about PHP. Since Java was originally designed with security in mind, there is little point in defending PHPs position. It is less secure. That's not to say that it's not worth considering PHP for your project, I personally have deployed numerous PHP projects with no security melt-downs (yet!)