intergerSet implements Comparable

Question

The purpose of this project is:

Create a class called IntegerSet that implements Comparable interface to be used in simple set applications. Each object of class IntegerSet can hold positive integers in the range 0 through 255 and most common set operations are available. A set must be represented internally as an int array of ones and zeros (or a boolean array). Array element a[ i ] is 1 if integer i is in the set and array element a[ j ] is 0 if integer j is not in the set.

and then add some member method to modify it.

I am not familiar with "implements Comparable interface," but here is what I got so far. The driver cannot test it, it shows "Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 256"

Can someone help me find out what the problem is? thanks!

import java.util.Arrays;
public class IntegerSet implements Comparable
{   
private int L = 256;
private int[] a = new int[L];

public IntegerSet()
{
    Arrays.fill(a, 0);
}

public IntegerSet(int n)
{
    a[n] = 1;
}

public IntegerSet(int[] n)
{
    a = n;
}


public IntegerSet union(IntegerSet other)
{
    int[] c = new int[L];
    for(int i = 0; i < L; i++)
    {
        if(this.a[i]==1 || other.a[i] ==1)
            c[i] = 1;
        else
            c[i] = 0;
    }
    IntegerSet temp = new IntegerSet(c);
    return temp;
}

public IntegerSet intersection(IntegerSet other)
{
    int[] c = new int[L];
    for(int i = 0; i < L; i++)
    {
        if(this.a[i]==1 && other.a[i] ==1)
            c[i] = 1;
        else
            c[i] = 0;
    }
    IntegerSet temp = new IntegerSet(c);
    return temp;
}

public IntegerSet difference(IntegerSet other)
{
    int[] c = new int[L];
    for(int i = 0; i < L; i++)
    {
        if(this.a[i] != other.a[i])
            c[i] = 1;
        else
            c[i] = 0;
    }
    IntegerSet temp = new IntegerSet(c);
    return temp;
}

public IntegerSet insertElement(int k)
{
    a[k] = 1;
    IntegerSet temp = new IntegerSet(a);
    return temp;
}

public IntegerSet removeElement(int k)
{
    a[k] = 0;
    IntegerSet temp = new IntegerSet(a);
    return temp;
}

public boolean isElement(int k)
{
    return(a[k] == 1);
}

public String toString()
{
    String str = "";
    for(int i = 0; i < L; i++)
    {
        if(a[i] == 1)
            str += (i + ", ");
    }
    return "{" + str + "}";
}

public IntegerSet copy()
{
    IntegerSet temp = new IntegerSet(a);
    return temp;
}

public boolean subset(IntegerSet other)
{
    boolean sub = true;
    int i = 0;
    while(sub)
    {
        if(this.a[i] == 1)
        {
            if(other.a[i] == 1)
                sub = true;
            else
                sub = false;
        }
        i++;
    }
    return sub;
}

public boolean superset(IntegerSet other)
{
    boolean sup = true;
    int i = 0;
    while(sup)
    {
        if(other.a[i] == 1)
        {
            if(this.a[i] == 1)
                sup = true;
            else
                sup = false;
        }
        i++;
    }
    return sup;
}

public void addAll()
{
    Arrays.fill(a, 1);
}

public void removeAll()
{
    Arrays.fill(a, 0);
}

public int compareTo(Object other) 
{
    // TODO Auto-generated method stub
    return 0;
}

}

and the driver:

public class IntegerSetDriver 
{
    public static void main(String[] args) 
    {
        IntegerSet s1, s2, s3, s4, s5; 
        s1 = new IntegerSet(); // s1 is an empty set, {} 
        s2 = new IntegerSet(5); // s2 is a set with one element, {5} 
        s1.insertElement(1); // s1 is now {1} 
        s3 = s1.copy(); // s3 is now {1} 
        s4 = s1.union(s2); // s4 is now {1, 5} and s1 is still {1} 
        s5 = s4.insertElement(8).removeElement(5); // s4 is now {1, 8} // s5 references s4 

        int result = s3.compareTo(s4); // result is -1 (or < 0) 
        boolean yes = s3.subset(s4); // yes should be true 
        s5.removeAll(); // s4 and s5 both reference same empty set, {} 
       s1.removeElement(500); // invalid element so ignore, s1 is still {1}
    }
}

Generics were introduced more than 10 years ago, and you still don't use them. Your class should implement `Comparable`. Then you'll have to decide when an IntegerSet is bigger, lower or equal to another IntegerSet, and implement these rules. Returning 0 always doesn't make any sense. And if you actually **read** the exception stack trace, you'll see that the exception has nothing to do with your compareTo method, which always returns 0 and has thus 0 chance of throwing an exception. — JB Nizet, May 08 '14 at 05:17

score 0 · Answer 1 · edited May 12 '14 at 22:18

0

You should check your bounds before adding/removing from your int[] a (i.e. 500 is not a valid index).

Also, look at your constructor IntegerSet(input[] n), you cannot just directly "assign" it like that. You need to parse the array and update your local a[] properly.

"n" ranges from 0-255 for values, whereas "a" should only be {1,0}.

A few other things need fixing too.

edited May 12 '14 at 22:18

Sunny Patel

7,830
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answered May 12 '14 at 21:56

nocturnaltek

1

intergerSet implements Comparable

1 Answers1