Java Program to Implement Sparse Array

This Java program is to Implement Sparse array. In computer science, a sparse array is an array in which most of the elements have the same value (known as the default value—usually 0 or null). The occurrence of zero elements in a large array is inefficient for both computation and storage. An array in which there is a large number of zero elements is referred to as being sparse.
Here is the source code of the Java program to implement sparse array. The Java program is successfully compiled and run on a Linux system. The program output is also shown below.

class List
{
    private int index;
    private Object value;
    private List nextindex;
 
    public List(int index)
    {
        this.index = index;
        nextindex = null;
        value = null;
    }
 
    public List()
    {
        index = -1;
        value = null;
        nextindex = null;
    }
 
    public void store(int index, Object value)
    {
        List current = this;
        List previous = null;
 
        List node = new List(index);
        node.value = value;
 
        while (current != null && current.index < index)
        {
            previous = current;
            current = current.nextindex;
        }
 
        if (current == null)
        {
            previous.nextindex = node;
        } else
        {
            if (current.index == index)
            {
                System.out.println("DUPLICATE INDEX");
                return;
            }
            previous.nextindex = node;
            node.nextindex = current;
        }
        return;
    }
 
    public Object fetch(int index)
    {
        List current = this;
        Object value = null;
        while (current != null && current.index != index)
        {
            current = current.nextindex;
        }
        if (current != null)
        {
            value = current.value;
        } else
        {
            value = null;
        }
        return value;
    }
 
    public int elementCount()
    {
        int elementCount = 0;
        for (List current = this.nextindex; (current != null); current = current.nextindex)
        {
            elementCount++;
        }
        return elementCount;
    }
}
 
public class SparseArray
{
    private List start;
    private int index;
 
    SparseArray(int index)
    {
        start = new List();
        this.index = index;
    }
 
    public void store(int index, Object value)
    {
        if (index >= 0 && index < this.index)
        {
            if (value != null)
                start.store(index, value);
        } else
        {
            System.out.println("INDEX OUT OF BOUNDS");
        }
    }
 
    public Object fetch(int index)
    {
        if (index >= 0 && index < this.index)
            return start.fetch(index);
        else 
        {
            System.out.println("INDEX OUT OF BOUNDS");
            return null;
        }
    }
 
    public int elementCount()
    {
        return start.elementCount();
    }
 
    public static void main(String... arg)
    {
        Integer[] iarray = new Integer[5];
        iarray[0] = 1;
        iarray[1] = null;
        iarray[2] = 2;
        iarray[3] = null;
        iarray[4] = null;
 
        SparseArray sparseArray = new SparseArray(5);
        for (int i = 0; i < iarray.length; i++)
        {
            sparseArray.store(i, iarray[i]);
        }
 
        System.out.println("NORMAL ARRAY");
        for (int i = 0 ; i < iarray.length; i++)
        {
            System.out.print(iarray[i] + "\t");
        }
 
        System.out.println("\nSPARSE ARRAY");
        for (int i = 0; i < iarray.length; i++)
        {
            if (sparseArray.fetch(i) != null)
                System.out.print(sparseArray.fetch(i) + "\t");
        }
        System.out.println("The Size of Sparse Array is " + sparseArray.elementCount());
    }
}

$javac SparseArray.java
$java SparseArray
 
NORMAL ARRAY
1	null	2	null	null	
SPARSE ARRAY
1	2	
The Size of Sparse Array 2