[Java] Class Hierarchy Design

Really good explanations, thanks. But... I don't need to code any functions. The ONLY thing that I need to do is design the class hierarchy and its methods.

Okay. Flashback, and I looked through your code properly with my lost knowledge. I'm unsure if the circuit-class should be defined as abstract or not. I think it should, as the resistance();-function is abstract, right?

That's the only "major" error I saw here. Apart from that, indentation, capital letter at start of classnames and similar are just minor errors that shouldn't make changes in the code, though it would be nice to have it looking pretty. Here's what I would change to the code:

 Spoiler

Code:

public abstract class Circuit {
    public abstract int resistance();
}

public class BasicCircuit extends Circuit {
    string name;
    int res;

    public BasicCircuit (string name, int res) {//constructor
        this.name = name;
        this.res = res;
    }

    public int resistance() {//redefine  or define resistance
        return res; //resistance is constant, doesn't need to calculate anything.
    }
}

public class SerialCircuit extends Circuit{
    List<Circuit> circuits;

    public SerialCircuit(List<Circuit> circuits){ //constructor
        this.circuits = circuits;
    }
    
    public int resistance(){ //define resistance
        int res = 0;
        foreach (Circuit c in circuits){//the sum of all the resistances of its subcircuits
            res += c.resistance(); //res = res + c.resistance();
        }
    return res;
    }
}

Edit:

 LISP

Code:

(defclass resistors ()
    ((resistors :accessor resistors
                :initarg :resistors)))
                
(defclass serial-resistors (resistors) ())
    
(defclass parallel-resistors (resistors) ())
    
(defmethod resistance (n) n)
    
(defmethod resistance ((c parallel-resistors))
    (/ (reduce #'+
        (mapcar #'(lambda (x) (/ (resistance x)))
            (resistors c)))))
    
(defmethod resistance ((c serial-resistors))
    (reduce #'+ (mapcar #'resistance (resistors c))))