I've set file associations to use jd eclipse class file editor for .class & .class without source, but I still can't see decompiled code. My eclipse setting
One thing is after I restart eclipse it will be reset to use class file viewer automatically, I don't know whether it's the root cause.
In eclipse preferences , go to File Associations and check association for .class/.class without source.If you see at the bottom , you will see "Associated editor" , in this select "JD Class file viewer" and set it as default. Most probably your problem would be solved.