Is Java worth adding to a Bali-focused trip?
Yes, if you want temples, cities, volcanoes and a different Indonesia from resort Bali. Java is not a quick garnish, though; Yogyakarta, Bromo and Ijen need time and transport discipline.
Answer
Java is often the part of an Indonesia trip that makes Bali feel less like the whole country. Yogyakarta brings temples, food, student-city energy and a strong cultural base. Bromo and Ijen bring volcano drama, but also early starts, long transfers and operator choices. The reward is real if you want Indonesia to be more than beaches, cafés and villas. The catch is that Java does not slot neatly into every Bali plan. Add it when you can give it enough days to breathe, not when you are already short on time and hoping a volcano sunrise will justify two exhausting transfers.