Java is the center of government and commerce for Indonesia. Most Indonesians live on this island, making it the most populated island in the world, even though it is far from being the biggest! 138 million people call this island home, with 2,756 people per square mile. In the archipelago, Java, at 49,535 square miles, lies between Sumatra to the west and Bali to the east. Borneo is north of Java. (Wikipedia)
Java is made up of four provinces: Banten, West Java, Central Java, and East Java. Banten used to be part of West Java, but became a separate province in 2000. Java also has two special districts: Jakarta and Jogjakarta. Jakarta is the capital and Jogjakarta is a special district because it is still governed by a pre-colonial monarchy, the Sultan of Jogjakarta. (Wikipedia)
The two largest ethnic groups in Indonesia, the Sundanese and the Javanese, call Java home. The Javanese are the largest ethnic group in Indonesia. They live in Central and East Java and consider Jogjakarta their cultural center. The Sundanese live mainly in West Java with Bandung as their center.
The Banten, Madurese, and Betawi also live on Java. The Madurese live in East Java and on the island of Madura. The Betawi are the original people of Jakarta. Their language is very similar to Indonesian but has Chinese, Arabic, and Dutch mixed in. Much of the slang in Jakarta comes from Betawi (Wikipedia). The Banten people live in the province of Banten. They are basically Sunda but have identified themselves as a different ethnic group since the Banten kingdom broke off from the Padjajaran kingdom of West Java. (Joshua Project)
A large number of Chinese Indonesians live in Java, especially in the bigger cities. The Chinese came to Indonesia about three generations ago. Although they are a minority in Indonesia, approximately 10% of the population, they own about 90% of the businesses.
Because Jakarta is the center of government and commerce, one will find people from all over the country. Bandung, a city about two hours southeast of Jakarta, has many universities and also brings people from all over Indonesia.
Most of Java is Muslim. On the East Java coast close to Bali there is a large number of Hindus. In the larger cities, such as Jakarta, Bandung, and Surabaya, there are large numbers of Christians and Buddhists. Christianity is also growing in the Sundanese area and in some rural areas of south-central Java there are quite a few Catholics (Wikipedia).