If you are just switching form CRS 3.x to 4.x you may notice the Execute Java Step is gone from the toolbox. You only really need it if you are trying to execure a java method that returns void ( doesn't return a value ) This is common with "setter" methods like clock.setTime( "12:00:00" ). It is a pain that it was removed but if you have a couple of alternatives.

First if your java method returns a value use the Set step so to call a method like String.valueOf( clock.getSeconds() ). You can get as trick as you want withe inline syntax now which you couldn't before.

The second is to open an old script that has a Execute Java Object step in it and copy and past the step from the old script into your new one. The step still exists for backward compatability but you can't add it to new scripts from the toolbox. It was another ill thought out feature change between versions