Weka examples how to create attribute with different types.

CreatingWekaAttributes.java

FastVector validNominalValues = new FastVector(2);
validNominalValues.addElement("male");
validNominalValues.addElement("female");
Attribute nominalAttribute = new Attribute("gender", validNominalValues);

FastVector nullFastVector = null;
Attribute stringAttribute = new Attribute("userId", nullFastVector);

Attribute numericAttribute = new Attribute("humidity");