Short answers, pulled from the story.
The island of Java was formed by the geologic subduction of the Australian Plate under the Sunda Plate. This tectonic process created a chain of volcanic mountains that runs as an east-west spine across the entire landmass.
Indonesian independence was recognized in 1949 following a struggle centered in Java after World War II. Jakarta serves as the capital city on the northwestern coast where four provinces and two special regions now administer the island.
Java has a combined total of 156.9 million people with a population density reaching nearly 1,183.5 people per square kilometer. The western third of the island has higher density of roughly 1,563 per square kilometer accounting for most population growth.
Only two ethnic groups are native to the island: the Javanese and Sundanese. A fourth group called the Betawi people speak a Malay dialect local to Jakarta and are descendants from various Indonesian archipelago ethnic groups mixed with foreign groups like Portuguese Dutch Arab Chinese and Indian.
There are 112 volcanoes in all and 35 of them remain active today. Mount Semeru stands as the highest volcano on the island at 3676 meters above sea level while Mount Merapi is the most active volcano which has erupted repeatedly throughout recorded history.