Java 中的多项式

Polynomials in Java

提问by Meat

My add method works, however when I create a new SparsePolynomialobject (at the bottom of the add method), the value of the newSparePolynomialchanges when I debug it and I can't figure out where the extra information is coming from. Can someone help me?

我的 add 方法有效，但是当我创建一个新SparsePolynomial对象（在 add 方法的底部）newSparePolynomial时，我调试它时更改的值并且我无法弄清楚额外信息来自哪里。有人能帮我吗？

Here is a copy of my code:

这是我的代码的副本：

import java.util.ArrayList;

public class SparsePolynomial {

    private ArrayList<Polynomial> polynomialarraylist = new ArrayList<Polynomial>();

    /**
     * Constructor to get values of an arraylist of integers
     * @param arraylist that contains the  integer values used for the polynomials
     */
    public SparsePolynomial(ArrayList<Integer> arrayList)
    {
        //MODIFIDED: polynomialarraylist
        //EFFECT: constructs the arraylist of polynomials based off the arraylist of integers
        insertIntoPolynomialArray(arrayList);
    }

    /**
     * Converts the elements of the integer array into polynomials
     * @param arrayList that contains the polynomials contents
     */
    private void insertIntoPolynomialArray(ArrayList<Integer> arrayList)
    {
        //MODIFIED: polynomialarray
        //EFFECT: inputs the values of the arrayList into the polynomial array based on the position of the digits
        for(int i = 0; i < arrayList.size(); i++)
        {
            Polynomial polynomial = new Polynomial(arrayList.get(i), arrayList.get(i+1));
            polynomialarraylist.add(polynomial);
            System.out.println("coef" + arrayList.get(i));
            System.out.println("degree" + arrayList.get(i+1));
            i++;
        }
    }


    /**
     * 
     */
    @Override
    public String toString() 
    {
        String result = "";
        sort();
        if (getDegree(0) ==  0) 
            return "" + getCoefficient(0);
        if (getDegree(0) ==  1) 
            return getCoefficient(0) + "x + " + getCoefficient(0);
        result =  getCoefficient(0) + "x^" + getDegree(0);

        for (int j = 1; j < polynomialarraylist.size(); j++) 
        {
            if(j > polynomialarraylist.size())
            {
                break;
            }
            if      
            (getCoefficient(j) == 0) continue;
            else if 
            (getCoefficient(j)  > 0) result = result+ " + " + ( getCoefficient(j));
            else if 
            (getCoefficient(j)  < 0) result = result+ " - " + (-getCoefficient(j));
            if(getDegree(j) == 1) result = result + "x";
            else if (getDegree(j) >  1) result = result + "x^" + getDegree(j);
        }
        return result;


    }

    /**
     * Sorts array 
     * @param array to sort
     */
    private void sort()
    {
        ArrayList<Polynomial> temp = polynomialarraylist;
        ArrayList<Polynomial> temp2 = new ArrayList<Polynomial>();
        int polydegreemain = polynomialarraylist.get(0).degree();
        temp2.add(polynomialarraylist.get(0));
        for(int i = 1; i < polynomialarraylist.size(); i++)
        {
            if(i > polynomialarraylist.size())
            {
                break;
            }
            int polydegreesecondary = polynomialarraylist.get(i).degree();

            if(polydegreemain < polydegreesecondary)
            {
                temp.set(i-1, polynomialarraylist.get(i));
                temp.set(i, temp2.get(0));
            }

        }

        polynomialarraylist = temp;
    }
    /**
     * Makes object hashable
     */
    @Override
    public int hashCode() {
        final int prime = 31;
        int result = 1;
        result = prime
                * result
                + ((polynomialarraylist == null) ? 0 : polynomialarraylist
                        .hashCode());
        return result;
    }

    /**
     * Checks for equality of two objects
     */
    @Override
    public boolean equals(Object obj) {
        if (this == obj)
            return true;
        if (obj == null)
            return false;
        if (getClass() != obj.getClass())
            return false;
        SparsePolynomial other = (SparsePolynomial) obj;
        if (polynomialarraylist == null) {
            if (other.polynomialarraylist != null)
                return false;
        } else if (!polynomialarraylist.equals(other.polynomialarraylist))
            return false;
        return true;
    }

    public boolean equals(SparsePolynomial Sparse)
    {
        if(this == Sparse)
        {
        return true;
        }
        else
        {
        return false;
        }
    }

    public SparsePolynomial add(SparsePolynomial other)
    {

        ArrayList<Polynomial> thisPolynomial = createPolynomial();
        SparsePolynomial newSparsePolynomial;
        ArrayList<Polynomial> otherPolynomial = other.createPolynomial();
        Polynomial oldsum = new Polynomial();
        Polynomial newsum = new Polynomial();
        for(int i = 0; i < thisPolynomial.size();i++)
        {
            if(thisPolynomial.size() == 1)
            {
                newsum = thisPolynomial.get(i);
                oldsum = newsum;
                break;
            }
            if(i == 0)
            {
            newsum = thisPolynomial.get(i).add(thisPolynomial.get(i+1));
            oldsum = newsum;
            i++;
            }
            else
            { 
                newsum = oldsum.add(thisPolynomial.get(i));
                oldsum = newsum;
            }
        }
        for(int i = 0; i < otherPolynomial.size(); i++)
        {       
            newsum = oldsum.add(otherPolynomial.get(i));
            oldsum = newsum;
        }

        ArrayList<Integer> ints = new ArrayList<Integer>();

        for(int i = 0; i < oldsum.degree()+1; i++)
        {
            ints.add(oldsum.coefficient(i));
            ints.add(i);
        }
        newSparsePolynomial = new SparsePolynomial(ints);

        return newSparsePolynomial;
    }

    public SparsePolynomial subtract(SparsePolynomial other)
    {
        ArrayList<Polynomial> thisPolynomial = createPolynomial();

        ArrayList<Polynomial> otherPolynomial = other.createPolynomial();

        Polynomial olddifference = new Polynomial();
        Polynomial newdifference = new Polynomial();
        for(int i = 0; i < thisPolynomial.size()+1;i++)
        {
            if(i == 0)
            {
                newdifference = thisPolynomial.get(i).subtract(thisPolynomial.get(i+1));
                olddifference = newdifference;
                i++;
            }
            else
            {
                newdifference = olddifference.subtract(thisPolynomial.get(i));
                olddifference = newdifference;
            }
        }
        for(int i = 0; i < otherPolynomial.size(); i++)
        {

            newdifference = olddifference.add(otherPolynomial.get(i));
            olddifference = newdifference;

        }

        ArrayList<Polynomial> polyarray = createArrayListOfPolynomialsFromPolynomials(olddifference);

        ArrayList<Integer> ints = new ArrayList<Integer>();

        for(int i = 0; i < polyarray.size(); i++)
        {
        ints.add(polyarray.get(i).coefficient(polyarray.get(i).degree()));
        ints.add(polyarray.get(i).degree());
        }

        SparsePolynomial newSparsePolynomial = new SparsePolynomial(ints);

        return newSparsePolynomial;
    }


    private int getDegree(int index)
    {
        int degree;

        degree = polynomialarraylist.get(index).degree();

        return degree;
    }

    private int getCoefficient(int index)
    {
        int coefficient;

        coefficient = polynomialarraylist.get(index).coefficient(polynomialarraylist.get(index).degree());

        return coefficient;
    }

    private ArrayList<Polynomial> createPolynomial()
    {
        Polynomial polynomial = null;
        ArrayList<Polynomial> polynomialArray = new ArrayList<Polynomial>();
        for(int i = 0; i < polynomialarraylist.size(); i++)
        {
            polynomial = new Polynomial(getCoefficient(i), getDegree(i));
            polynomialArray.add(polynomial);        
        }
        return polynomialArray;
    }
Polynomial class

public class Polynomial {
    // Overview: ...
    private int[] terms;
    private int degree;

    // Constructors
    public Polynomial() {
        // Effects: Initializes this to be the zero polynomial
        terms = new int[1];
        degree = 0;
    }

    public Polynomial(int constant, int power) {
        // Effects: if n < 0 throws IllegalArgumentException else
        //  initializes this to be the polynomial c*x^n
        if(power < 0){
            throw new IllegalArgumentException("Polynomial(int, int) constructor");
        }

        if(constant == 0) {
            terms = new int[1];
            degree = 0;
            return;
        }

        terms = new int[power+1];

        for(int i=0; i<power; i++) {
            terms[i] = 0;
        }

        terms[power] = constant;
        degree = power;
    }

    private Polynomial(int power) {
        terms = new int[power+1];
        degree = power;
    }

    // Methods
    public int degree() {
        // Effects: Returns the degree of this, i.e., the largest exponent
        //  with a non-zero coefficient.  Returns 0 is this is the zero polynomial
        return degree;
    }

    public int coefficient(int degree) {
        // Effects: Returns the coefficient of the term of this whose exponent is degree
        if(degree < 0 || degree > this.degree) {
            return 0;
        }
        else {
            return terms[degree];
        }
    }

    public Polynomial subtract(Polynomial other) throws NullPointerException {
        // Effects: if other is null throws a NullPointerException else
        //  returns the Polynomial this - other
        return add(other.minus());
    }

    public Polynomial minus() {
        // Effects: Returns the polynomial - this
        Polynomial result = new Polynomial(degree);
        for(int i=0; i<=degree; i++) {
            result.terms[i] = -this.terms[i];
        }
        return result;
    }

    public Polynomial add(Polynomial other) throws NullPointerException {
        // Effects: If other is null throws NullPointerException else
        //  returns the Polynomial this + other
        Polynomial larger, smaller;
        if (degree > other.degree){
            larger = this;
            smaller = other;
        }
        else {
            larger = other;
            smaller = this;
        }

        int newDegree = larger.degree;

        if (degree == other.degree) {
            for(int k = degree; k > 0 ; k--) {
                if (this.terms[k] + other.terms[k] != 0) {
                    break;
                }
                else {
                    newDegree --;
                }
            }
        }


        Polynomial newPoly = new Polynomial(newDegree);
        int i;
        for (i=0; i <= smaller.degree && i <= newDegree; i++){
            newPoly.terms[i] = smaller.terms[i] + larger.terms[i];
        }

        for(int j=i; j <= newDegree; j++) {
            newPoly.terms[j] = larger.terms[j];
        }

        return newPoly;
    }

    public Polynomial multiply(Polynomial other) throws NullPointerException {
        // Effects: If other is null throws NullPointerException else
        //  returns the Polynomial this * other
        if ((other.degree == 0 && other.terms[0] == 0) ||
                (this.degree==0 && this.terms[0] == 0)) {
                    return new Polynomial();
        }

        Polynomial newPoly = new Polynomial(degree + other.degree);

        newPoly.terms[degree + other.degree] = 0;

        for(int i=0; i<=degree; i++) {
            for (int j=0; j<= other.degree; j++) {
                newPoly.terms[i+j] = newPoly.terms[i+j] + this.terms[i] * other.terms[j];
            }
        }
        return newPoly;
    }

回答by Falmarri

At quick glance, looks like this is a problem

乍一看，看起来这是一个问题

for(int i = 0; i < arrayList.size(); i++)
{
    Polynomial polynomial = new Polynomial(arrayList.get(i), arrayList.get(i+1));
    polynomialarraylist.add(polynomial);
    System.out.println("coef" + arrayList.get(i));
    System.out.println("degree" + arrayList.get(i+1));
    i++;
}

You're doing i++ twice here.

你在这里做了两次 i++。

Also, you posted WAY too much code. No one wants to read that much. You're just lucky that, assuming this is the problem, I happened to glance at that.

此外，您发布了太多代码。没有人想读那么多。你很幸运，假设这是问题所在，我碰巧瞥了一眼。

Also that will throw an arrayindexoutofboundserror since you're doing .get(i+1)

这也会抛出一个 arrayindexoutofboundserror 因为你在做 .get(i+1)

回答by Meat

the constructor is set up the way it is because the get(i) gets you the coefficient and the i+1 gets you the degree from the arraylist parameter since when you call add, without those the arraylist contents would be off

构造函数的设置方式是因为 get(i) 为您提供系数，而 i+1 为您提供来自 arraylist 参数的度数，因为当您调用 add 时，如果没有这些，则 arraylist 内容将关闭

THe constructor is suppose to take an Arraylist and put them inisde of an arraylist of polynomials. using the odds as the coefficient and the evens as the degrees of the polynomials.

构造函数假设采用一个 Arraylist 并将它们放入多项式数组列表中。使用赔率作为系数，将偶数作为多项式的次数。