Pfthb

I am trying to iterate through two Linked lists using a for loop and the listIterator method.

I am trying to accomplish the method below which adds two polynomials using a linked list

public Polynomial add(Polynomial p)

POSTCONDITION: this object and p are not changed
return a polynomial that is the sum of p and this polynomial

Here is my method

public Polynomial add( Polynomial p )

 // use the copy constructor
 Polynomial answer = new Polynomial( this );
 // answer.termList.addAll(p.termList);
 // use addAll()
 //answer=this.termList.addAll(p.termList);
 //ListIterator<Term> itr = answer.termList.listIterator();
 //ListIterator<Term> itr = answer.termList.listIterator();
 //ListIterator<Term> itr2 = p.termList.listIterator();
 for ( ListIterator<Term> itr = answer.termList.listIterator(); itr.hasNext(); )
 
 Term term = itr.next();

 for ( ListIterator<Term> itr2 = p.termList.listIterator(); itr2.hasNext(); )
 
 Term term2 = itr2.next();
 if ( term.exponent == term2.exponent )
 
 answer.itr.coefficient = answer.itr.coefficient + p.itr2.coefficient;
 
 
 /**while ( itr.hasNext() )
 
 Term term = itr.next();
 **/
 return answer;

 

This line for (ListIterator<Term> itr=answer.termList.listIterator();itr.hasNext();) and for(ListIterator<Term> itr2 = p.termList.listIterator(); itr2.hasNext();) have errors.

I keep getting an error that says itr and itr2 cannot be resolved or is not a field.

Here is part of the code that defines Polynomial there are a lot of methods which I didn't include since they are too long.

public class Polynomial implements Cloneable

 // this is a nested static class, it defines a type
 // all the instance varaibles can be access directly inside Polynomial
 // class even though they have

 // private modifier
 private static class Term
 
 private int exponent;
 private double coefficient;

 public Term( int exp, double coeff )
 
 coefficient = coeff;
 exponent = exp;
 
 

 // instance variables of Polynomial
 // first is the term of the Polynomial with the highest degree
 private LinkedList<Term> termList;

 /**
 * Postcondition: Creates a polynomial which is 0.
 **/
 public Polynomial()
 
 termList = new LinkedList<Term>();
 termList.add( new Term( 0, 0 ) );
 

 /**
 * Postcondition: Creates a polynomial which has a single term
 * a0*x^0
 *
 * @param a0 The value to be set as the coefficient of the
 * constant (x^0) t erm.
 **/
 public Polynomial( double a0 )
 
 termList = new LinkedList<Term>();
 termList.add( new Term( 0, a0 ) );
 

This is the faulty line

answer.itr.coefficient= answer.itr.coefficient + p.itr2.coefficient;

itr and itr2 are iterator objects and not members of Polynomial, I guess what you meant was

term.coefficient += term2.coefficient;

Update

For completeness here is my full version of the add method

public Polynomial add(Polynomial p) 
 Polynomial answer = new Polynomial(this);
 for (ListIterator<Term> itr = answer.termList.listIterator(); itr.hasNext();) 
 Term term = itr.next();

 for (ListIterator<Term> itr2 = p.termList.listIterator(); itr2.hasNext();) 
 Term term2 = itr2.next();
 if (term.exponent == term2.exponent) 
 term.coefficient += term2.coefficient;
 else 
 answer.termList.add(new Term(term2.exponent, term2.coefficient));
 
 
 
 return answer;

The loops don't have to be nested.

This solution will keep the terms sorted by descending order of the exponent:

public class Polynomial 
 private List<Term> termList = new LinkedList<Term>();

 private static class Term 
 private int exponent;
 private double coefficient;

 private Term(int exponent, double coefficient) 
 this.exponent = exponent;
 this.coefficient = coefficient;
 
 

 public Polynomial() 
 

 public Polynomial(int exponent, double coeff) 
 if (coeff != 0) 
 termList.add(new Term(exponent, coeff));
 
 

 public Polynomial add(Polynomial other) 
 Polynomial answer = new Polynomial();
 Iterator<Term> itr = termList.iterator();
 Iterator<Term> itr2 = other.termList.iterator();
 Term t = itr.hasNext() ? itr.next() : null;
 Term t2 = itr2.hasNext() ? itr2.next() : null;
 while (true) 
 if (t == null) 
 if (t2 == null) 
 break;
 
 answer.termList.add(new Term(t2.exponent, t2.coefficient));
 t2 = itr2.hasNext() ? itr2.next() : null;
 else if (t2 == null) 
 answer.termList.add(new Term(t.exponent, t.coefficient));
 t = itr.hasNext() ? itr.next() : null;
 else if (t2.exponent > t.exponent) 
 answer.termList.add(new Term(t2.exponent, t2.coefficient));
 t2 = itr2.hasNext() ? itr2.next() : null;
 else if (t2.exponent < t.exponent) 
 answer.termList.add(new Term(t.exponent, t.coefficient));
 t = itr.hasNext() ? itr.next() : null;
 else 
 answer.termList.add(
 new Term(t.exponent, t.coefficient + t2.coefficient));
 t = itr.hasNext() ? itr.next() : null;
 t2 = itr2.hasNext() ? itr2.next() : null;
 
 
 return answer;