jvm - IS there a way to turn off JIT compiler and is there a performance impact by doing so?

Question

What does it mean for a java program to be JIT'ed and does it make the execution a lot more faster or are there bytecodes which are not JIT'ed?

Answer 1

There is two ways to disable the JIT

-Djava.compiler=NONE 

or this will almost never compile anything

-XX:CompileThreshold=2000000000

or on IBM JVM

-nojit

Disabling the JIT can slow down your code a lot e.g. 50x but not always. If you spend most of your time doing IO or GUI updates you might find it makes little difference.