Dynamically update a member based on other member in class

This is my class

 public class Cars{

    public double Len;
    public List<Double> vehicle;

setters and getters

public List<Double> getVehicle() {
        return vehicle;
    }
public void setVehicle(List<Double> vehicle) {
    this.vehicle= vehicle;
    this.Len = this.vehicle.size();

} 

public double getLen() {
        return Len;
    }

public void setLen(double Len) {
    this.Len = Len;             
}   

}

Is it possible to update the member Len with length of position List of vehicles .