The ancient people of Java since 3000 years BC had known the wet-rice cultivation. This system of agriculture requires a smooth cooperation between villagers, is still being practiced to this day. The villagers must have a very high consciousness to organize such a complicated arrangement to be a smooth cooperation, benefited all parties involved. Besides the wet-rice cultivation, they have known also among other fishery, astronomy, cloth weaving, batik, gamelan & wayang. 

Before the arrival of Hinduism and any other world religions, the Javanese had already a culture & belief(s) of their own.

In some Javanese traditional ceremonies, ancient rituals remain in place to this day. It is a proof that Javanese people are smart in preserving their precious identity. Besides the existence of widely recognized religions such as Hinduism, Buddhism, Islam & Christianity, a local belief popularly known as Kejawen or Kebatinan does continue to exist.

Kejawen from the word Jawa (Java) : Javanism, is a Javanese spiritual knowledge in search of good & correct way of life, so the persons practicing the teaching correctly & wholeheartedly should find the spiritual way to true life (urip sejati => urip = life, sejati = true) achieving the harmonious relation between servant & God, JUMBUHING KAWULO GUSTI (jumbuh = a good, harmonious relation, kawulo = servant, gusti = Lord, God).

This is Kasunyatan - The Reality, Kebatinan from the word Batin = inner, spiritual. Kebatinan = spiritualism, generally understood as the spiritual teaching of belief in one God.
Some are of the opinion that Kejawen has a broader meaning than Kebatinan, except kebatinan it consists, also of way of thinking, art, tradition, culture etc.

The existence of Kejawen, in no way can be separated from the Javanese way of life & thinking, the nature & the tradition.

A Javanese concept prevails to this day is Mamayu Hayuning Bawono - to preserve the beauty of the world in a broader sense means to preserve the universe for the welfare of its inhabitants.
By nature, a Javanese is an environmentalist, a preserver of nature as clearly shown in their natural oriented tradition & rituals.

Living in harmony is of prime important - the harmonious relation among people in the society: between human beings and the universe & harmonious relation between servant & God.

Since their tender ages, the Javanese have been educated by their parents, families, society, teachers etc, the lessons of belief in God, moral behavior & etiquettes etc.
The elder Javanese always say that all religions are good. So far there is no conflict in Java due to religious differences.

Up to present date, the four royal palaces in Yogyakarta & Surakarta (Kasultanan under King/Sultan Hamengku Buwono X, Pakualaman under Viceroy/Adipati Pakualam IX, Kasunanan under King/Sunan Paku Buwono XII, Mangkunagaran under Viceroy/Adipati Mangkunagara IX) are the centers of Javanese court culture, where royal ceremonies from the old days are still performed.
The people culture such as "The Village Cleansing" ceremonies dated back from ancient period take place almost intactly.