How to write a intersection and union methods for sets in Java

Question

I'm new to using sets and for one of the exercise to learn how to use sets, I have been given a template file "SetInt" and a completed test file "TestSetInt". I know that I should use retainAll() and addAll() but the test class has asked me to write methods. Anyone have any idea how to write these two methods? Any help would be appreciated.

SetInt is the file which I have to add methods to and goes as follows:

public class SetInt 
{
    int[] setArray = new int[52];

public void add(int a)
{
    if (a < setArray.length-2)
    {
        setArray[a] = a;
    }
}
/* add a to the set in the correct position
 *@param a the value to be added
 **/    

public SetInt intersection(SetInt anySet)
{       
    return anySet;
}
/* returns the set of integers common to both
 * the set passed in as an argument and the set the
 * method is called on
 * @param anySet - the set to be intersected
 * @return a set containing the result of the intersection
*/

public SetInt union(SetInt anySet)
{   
    return anySet;
}
/* returns the set of integers which are in either the 
 * set passed in as an argument or the set the method
 * is called on
 * @param anySet - one of the sets in the union
 * @return a set containing the result of the union
*/

}

Here is TestSetInt, a file provided for me which I have to run to see if my methods work correctly:

public class TestSetInt
{
    public TestSetInt()
    {
        SetInt test1 = new SetInt();
        SetInt test2 = new SetInt();

//      adding numbers to the 2 sets
        for(int i = 2; i<49;i=i+3)
        {
            test1.add(i);
        }
        System.out.println();

        for(int i = 2; i<49;i=i+4)
        {
            test2.add(i);
        }
        System.out.println();

//      testing intersection
        SetInt interx = new SetInt();
        interx=test2.intersection(test1);

//      testing union       
        SetInt unionx = test1.union(test2);

    }

    public static void main (String args[])
    {
        TestSetInt practice = new TestSetInt(); 
    }
}

Answer 1

this works :)

SetInt Class

public class SetInt {
    int[] setArray = new int[52];

    public void add(int a) {
        if (a < setArray.length - 2) {
            setArray[a] = a;
        }
    }

    /*
     * add a to the set in the correct position
     * 
     * @param a the value to be added
     */

    public SetInt intersection(SetInt anySet) {
        SetInt temp = new SetInt();
        for (int i = 0; i < setArray.length; i++) {
            for (int j = 0; j < anySet.setArray.length; j++) {
                if (setArray[i] == anySet.setArray[j]) {
                    temp.setArray[i] = setArray[i];
                }
            }
        }
        return temp;
    }

    /*
     * returns the set of integers common to both the set passed in as an
     * argument and the set the method is called on
     * 
     * @param anySet - the set to be intersected
     * 
     * @return a set containing the result of the intersection
     */

    public SetInt union(SetInt anySet) {
        SetInt temp = new SetInt();
        for (int i = 0; i < setArray.length; i++) {
            for (int j = 0; j < anySet.setArray.length; j++) {
                temp.setArray[i] = setArray[i];
                if (anySet.setArray[j] != 0) {
                    temp.setArray[j] = anySet.setArray[j];
                }
            }
        }
        return temp;
    }
    /*
     * returns the set of integers which are in either the set passed in as an
     * argument or the set the method is called on
     * 
     * @param anySet - one of the sets in the union
     * 
     * @return a set containing the result of the union
     */

}

TestSetInt

public class TestSetInt {
    public TestSetInt() {
        SetInt test1 = new SetInt();
        SetInt test2 = new SetInt();

        // adding numbers to the 2 sets
        for (int i = 2; i < 49; i = i + 3) {
            test1.add(i);
        }
        printSetInt(test1);

        for (int i = 2; i < 49; i = i + 4) {
            test2.add(i);
        }
        printSetInt(test2);

        // testing intersection
        SetInt interx = new SetInt();
        interx = test2.intersection(test1);
        printSetInt(interx);

        // testing union
        SetInt unionx = test1.union(test2);
        printSetInt(unionx);

    }

    public void printSetInt(SetInt set) {
        for (int i : set.setArray) {
            System.out.print(i + ",");
        }
        System.out.println();
    }

    public static void main(String args[]) {
        TestSetInt practice = new TestSetInt();
    }

}