Weka is a collection of machine learning algorithms for data mining tasks. The algorithms can either be applied directly to a dataset or called from your own Java code. Weka contains tools for data pre-processing, classification, regression, clustering, association rules, and visualization. It is also well-suited for developing new machine learning schemes.

To use any of the feature selection methods programmatically you have to use the class weka.filters.supervised.attribute.AttributeSelection

Source: Weka FAQ