Add.java

import ec.EvolutionState;
import ec.Problem;
import ec.gp.ADFStack;
import ec.gp.GPData;
import ec.gp.GPIndividual;
import ec.gp.GPNode;

public class Add extends GPNode
{
    public String toString() { return "+"; }

    public int expectedChildren() { return 2; }

    public void eval(final EvolutionState state,
                     final int thread,
                     final GPData input,
                     final ADFStack stack,
                     final GPIndividual individual,
                     final Problem problem)
    {
        double result;
        DoubleData data = ((DoubleData)(input));

        children[0].eval(state,thread,input,stack,individual,problem);
        result = data.x;

        children[1].eval(state,thread,input,stack,individual,problem);
        data.x = result + data.x;
    }
}