Which ocean is Java sea?

Java Sea, Indonesian Laut Jawa, portion of the western Pacific Ocean between the islands of Java and Borneo.

It is a part of Borneo? Are there beaches in Borneo connected to Java Sea?

Borneo beaches are mainly in the eastern state of Sabah including Tunku Abdul Rahman National Park’s beaches, Tanjung Aru Beach and Shangri La Rasa Ria Beach near the major city of Kota Kinabalu. In the western state of Sarawak there is the rustic Permai Rainforest Resort with a wonderful private beach.