Creating a polynomial linked list program for adding/subtracting/multiplying polynomials?

I've attached the code below with TODO with the parts I am stuck on:

/** * Polynomial Class which implements the CalculatorOperand interface. * Maintains polynomials as an ordered linked list, with monomials arranged by decreasing degree */

public class Polynomial implements CalculatorOperand {

private class PolyNode { int coeff; int degree; PolyNode next;

PolyNode(int c, int d) { coeff = c; degree = d; } }

private PolyNode monomialsList; // TODO: initialize in the constructor Polynomial(int coeff, int degree) { // TODO: IMPLEMENT PolyNode newNode = new PolyNode(coeff, degree); }

/** * Returns this + coeff*x^degree * that; does not modify this or that. Assumes coeff is nonzero. */ // NOTE: normally, this would be private, but leave it public so we can test it public Polynomial addTimesMonomial (Polynomial that, int coeff, int degree) { return null; // TODO: IMPLEMENT; READ THE ASSIGNMENT AND IMPLEMENT add FIRST }

/** * Returns this+that; does not modify this or that */ public Polynomial add (Polynomial that) { return null;// TODO: IMPLEMENT }

/** * Returns this-that; does not modify this or that */ public Polynomial subtract (Polynomial that) { return null; // TODO: IMPLEMENT }

/** * Returns this*that; does not modify this or that */ public Polynomial multiply (Polynomial that) { return null; }

/** * Prints the polynomial the way a human would like to read it * @return the human-readable string representation */ public String toString () { if (monomialsList.next == null) return "0";

String ret = monomialsList.next.coeff<0 ? "-" : ""; for (polynode p = monomialsList.next; p!=null; { if (p.degree 0 || (p.coeff! =1 && p.coeff! =-1)) ret=ret + java.lang.math.abs(p.coeff) ;> 0) ret = ret + "x"; if (p.degree > 1) ret = ret + "^" + p.degree; if (p.next != null) ret = ret + (p.next.coeff<0 ? " - " : " + "); } return ret; } }