The drawbacks of basic Java use
The script above demonstrates a very simple way of bringing PHP and Java together, however it has two fatal flaws: each piece of Java code is sent independently, and there are coding limitations as to what can be achieved.
Sending chunks of Java code piece by piece means that the Java compiler has to read the line in, convert it to byte code, optimise it, then execute it. This has two implications: firstly, code in loops will need to be re-sent, re-read, re-converted, re-optimised, and executed each time the loop iterates, and secondly the Java compiler is not able to group optimisations together across pieces of code because it must act upon each individual line as it receives them. Combined together these two mean that Java sent through PHP is much slower than normal compiled Java.
Furthermore, the basic Java technique shown above only allows you to use existing Java objects - you cannot actually use Java code, or implement your own classes.