As far as I know Jetbrains PHPStorm is programmed in Java but while I don’t have Java installed in my Windows 7 PC, PHPstorm is installed and working without any problem.
How It’s done?
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JetBrains bundles the version of the JDK that the IDE needs with it. This is true for all of the different IDEs that they make.
The reason for this is to make sure that they are running with the JDK that the IDE is designed for. If you look in the location where the IDE is installed (IDE_HOME) you will find the JRE that it is bundled with in the JRE directory.
It is recommended to use the JDK that is bundled with it unless there are specific issues that need to be handled (IT security policy, bug fix for a specific bug critical to the application).
Both running too new a JDK or to old a JDK can cause problems. For example, at one time the JDK 1.7 from Oracle didn’t support retina graphics on the Mac and would cause JetBrains products to not launch (from SO – the comments seem to imply that there are still font issues with recent versions).
So, by bundling the JDK one can be sure that its there and is the right version. That everything works as intended and that when someone calls in with a support question you can ask “Have you set the JDK to a different version than it was bundled with?” instead of “What version of the JDK are you running with?”
All this fits together to make a better user experience (you didn’t have to go about trying to find the proper version of the JDK to download and install and configure the environment path… or juggle the environment path) and supportability.
As noted in this Jetbrains KB document this isn’t universally true, because some operating systems (Mac OS X in particular) have a JDK bundled with them that the application can count on being there and being the version that the application is built against.