Jakarta the capital of Indonesia, is different from other areas of Java. This city has a population of around 10 million or 20 million, including the suburbs. Jakarta today consists of a mix of culture and people where many ethnicities, not only from Java but Sumatra, Borneo and other places live together.
There are 6 regions/provinces in Java. From the west side, Banten, Special Territory of Jakarta (the capital of Indonesia), West Java (the province's capital is Bandung), Middle Java (the province's capital is Semarang), Special Territory of Yogyakarta (a capital of Javanese Kingdom, the other being Surakarta or Solo) and East Java (the province's capital is Surabaya)
Central Java and Yogyakarta
This is a more subjective description of the region -- what it's like, why someone would want to go there, the culture and atmosphere, the history, the weather, what makes it different and distinct from other regions.