Question

I have a test code for an ADT of LinkedList, which implements interface NumList.java, and is implemented in a NumLinkedList.java, and am using it in a NumSet.java.

I am trying to make it so that my NumSet has methods where I can create a set from a double array input, and use intercept/union and print methods to use and print the data.

but my test code is showing that my test NumSet values are empty, namely testProof and testProof2.

So now my testProof is returning an empty variable, which means nothing is saving into it.

static public NumSet intersect(NumSet S1, NumSet S2) //check 2nd for and if//
{
    NumSet intersectAnswer = new NumSet();

    for (int i = 0; i < S1.set.size()-1; i++)
    {
        for(int j = 0; j < S2.set.size()-1; j++)
        {
            double FUZZ = 0.0001;
            if (Math.abs(S1.set.lookup(i) - S2.set.lookup(j)) < FUZZ) // double values, this is more precise than ==.
                {
                    intersectAnswer.set.insert(1, S1.set.lookup(i));
                }
        }
    }

    return intersectAnswer;

}

is the method for testProof, and the following is where testProof is defined.

public static void main(String[] args)
{
    double[] a = {1.3,2,3,4,101.9};
    double[] b = {3,7,13,901,-29.1,0.05};

    NumArrayList test;
    test = new NumArrayList();
    test.printTest(); //runs test code in NumList


    //ok below is running. what is wrong with intersect?
    NumSet test2;
    test2 = new NumSet(a);
    NumSet test4;
    test4 = new NumSet(b);
    NumSet testProof;
    NumSet testProof2;

    test2.print(); //print out test 2
    System.out.println();
    test4.print();
    System.out.println();
    testProof = intersect(test2,test4);

I have initialized as

public class NumSet
{
private NumList set;

    public NumSet(double[] sth)
    {
        //moves elements of sth into set.
        set = new NumLinkedList();
        for(int i = 0; i < sth.length; i++)
        {
            set.insert(0,sth[i]);
        }
        set.removeDuplicates();
    }

    public NumSet()
    {
        set = new NumLinkedList();
    }

int numSet = 0;

and my intercept, union and print are below:

public NumSet intersect(NumSet S1, NumSet S2) //check 2nd for and if//
{
    NumSet intersectAnswer = new NumSet();

    for (int i = 0; i < S1.set.size()-1; i++)
    {
        for(int j = 0; j < S2.set.size()-1; j++)
        {
            if (S1.set.lookup(i) == S2.set.lookup(j))
                {
                intersectAnswer.set.insert(0, S1.set.lookup(i));
                }
        }
    }

    // intersectAnswer.set.removeDuplicates();  unnecessary, sets are already removed of duplicates
    return intersectAnswer;

}

public NumSet union(NumSet S1, NumSet S2)
{   //check logic.
    NumSet unionAnswer = new NumSet();

    for (int i = 1; i < S1.set.size()+1; i++)
    {
        unionAnswer.set.insert(1, S1.set.lookup(i));
    }

    for (int i = 1; i < S2.set.size()+1; i++)
    {
        unionAnswer.set.insert(1, S2.set.lookup(i)); 
    }
    unionAnswer.set.removeDuplicates();
    return unionAnswer;
}

public void print() 
{
    for (int i = 0; i < set.size()-1; i++)
    {
        System.out.print(set.lookup(i) + ",");

    }
    System.out.print(set.lookup(set.size()-1));
}

the lookup and size are referred to from my NumLinkedList.java and are as below

public int size() // measure size of list by counting counter++;
{


    return nItem; 
}


public double lookup(int i) 
{
    if( i <0 || i >= size()) //cannot lookup nonexistant object
    {
        System.out.println("out of bounds " + i + " < 0 or > " + size() );
        //how do I break out of this loop?
        System.out.println("just returning 0 for the sake of the program");

        return 0;
    }

    if(i == 0)
    {
        return head.value;
    }

    double answer = 0;
    Node currNode = head;
    for(int j = 0; j < i+1; j++) //move to ith node and save value
    {
        answer = currNode.value;    
        currNode = currNode.next;   
    }

    return answer;
}

and finally my test code is as below, where testProof and testProof2 are.

public static void main(String[] args)
{
    double[] a = {1.3,2,3,4,101.9};
    double[] b = {3,7,13,901,-29.1,0.05};

    NumArrayList test;
    test = new NumArrayList();
    test.printTest(); //runs test code in NumList


    //ok below is running. what is wrong with intersect?
    NumSet test2;
    test2 = new NumSet(a);
    NumSet test4;
    test4 = new NumSet(b);
    NumSet testProof;
    NumSet testProof2;

    test2.print();
    System.out.println();
    testProof = test2.intersect(test2, test4);
    System.out.println("tried intersect");
    testProof.print(); 
    System.out.println();
    System.out.println("tried test.print()");
    testProof2 = test2.union(test2,test4);
    System.out.println("tried union");
    testProof2.print(); 
    System.out.println();
    System.out.println("NumSet ran fully.");

Answer 1

I’d suggest you implement you NumSet Class with integer values rather than double values while you debug because comparing two double values tends to add some unneeded complexity to your code at this debug stage.

You might want to look at your removeDuplicates() method, I think that might hold the answer to your problem. Unfortunately I don’t see it within the code you posted.

Actually, this part of code within the intersect() method is destined to fail from the start,

if (S1.set.lookup(i) == S2.set.lookup(j))

Because of your use of doubles, == is a very imprecise method of comparing two different values, a better way would be to allow for a certain amount of precision error, i.e.

double final FUZZ = 0.0001
if (Math.abs(S1.set.lookup(i) - S2.set.lookup(j)) < FUZZ )
    //...