How can i recognize that my java finch will lay eggs ? What activity will they have at that time ?

If your java finches have a nest box, they will become interested in it and, if they've mated, the female should lay eggs soon. If they don't have a nest box, they will use newspaper, feathers, or millet to build a nest. Java finches usually lay 5-7 eggs. Both the male and female incubate the eggs for around 14-18 days.