Java, then part of the Dutch colony of the Netherlands East Indies, had for many decades grown quality coffee, particularly in East Java. When the price of coffee dropped disastrously, Dutch coffee growers found themselves in straits. Many were forced to sell up. Those who managed to survive followed the Malayan example and switched to rubber. Jungle may have to be cleared, derelict estates re-planted, roads built, buildings and processing plant erected, fencing, drainage, water and power supplies laid on.
Housing has to be erected for managers and estate workers.
Most of this infrastructure has to be in place before a nursery for rubber seedlings is established. Later, when the seedlings are sturdy enough to be planted out, another five or six years must elapse before the trees are sufficiently mature for tapping to begin. My father, whose working life was spent in rubber, remarked that from seed to tapping takes seven years. During these years the plantation and its staff have to be maintained. Plantation owners therefore have to face a considerable delay before they can expect any return for the money and effort they have invested in their rubber trees, though a secondary crop like coffee may help by bringing in some income.