This excerpt from my profile of this plant species may help illustrate what Colin said.
Once established, Java Fern reproduces by adventitious plants at the tips of the fronds (leaves). The plantlets may be pulled away from the frond when they have a few fronds and roots; if left, the frond tip will eventually darken and the daughter plant will break away and drift until the roots are able to attach themselves to an object. The plant may also be propagated by cutting the rhizome (ensuring there are a few fronds and roots attached to each piece) and affixing it elsewhere.