The reason for this is obvious, the south coast was not known.

Java, indeed, was believed to be connected with the Great Southern Continent, and was called _Java Major_, to distinguish it from Sumatra, which was named _Java Minor_.
In proof of the Portuguese belief concerning the connection and size of Java, I quote here what Camoens, their immortal poet, says:-- _"Olha a Sunda* tao larger, que huma banda Esconde pare o Sul difficultuoso." Os Lusiadas._ Java behold, so large that one vast end It, covers towards the South tempestuous.
[* Another name for Java.] Towards the year 1570, however, practical Portuguese seamen had become aware of a more accurate shape for Java, and Diego do Couto, the Portuguese historian, describes its shape in the following manner:-- "The figure of the island of Java resembles a pig couched on its fore legs, with its snout to the Channel of Balabero,* and its hind legs towards the mouth of the Straits of Sunda, which is much frequented by our ships.

The southern coast, [pig's back] is not frequented by us, and its bays and ports are not known; but the northern coast [pig's stomach] is much frequented, and has many good ports." [* Modern Straits of Bali.].