"If a well-to-do, stand-up ethical person
would be thrown into a poor city with nothing,
deprived of all his resources,
there is a high probability
that this person would start to lie,
to cheat and to steal, just in order to survive."
Zeitgeist Orientation Guide
As mentioned at other parts of this website, people are different and it's difficult to describe a population as a whole. There are reasonable and intelligent people on Java, no doubt. There are moderate and kind people, who have good manners. It's only, that they are extremely rare on Java. A thoroughly rotten mentality of dishonesty and fraud is predominant here.
Just while I write this sitting in a restaurant there is a man behind me noisily burping and chumping. Not for a moment - for long. Such and many other much more weird observations suffers the traveller every day manyfold.
A slum in Surabaya. Image: Asienreisender, 2012
Generally, that's here as it is mostly everywhere, people in the countryside are much more friendly and relaxter than people in the urban centers. On Java there is not much countryside left. It's said, Java would be the most overpopulated island in the world. The cities are big, and towns and villages stretch everywhere over the countryside, interrupted by rice paddies and impassable mountains. Almost all what is not urbanized is cultivated until high up into the mountains. That comes together with a high traffic level even on remoter areas.