A sparse array is a data structure that is used to efficiently store arrays that contain mostly empty or default values. This reduces memory usage and improves performance when working with large arrays that have a majority of empty elements.

In Java, we can create a sparse array by using a Map implementation, such as HashMap or TreeMap, where the keys represent the indices of the array and the values represent the corresponding elements.

Let’s see an example of how to create a sparse array in Java using a HashMap:

import java.util.HashMap;
import java.util.Map;

public class SparseArrayExample {
    public static void main(String[] args) {
        Map<Integer, String> sparseArray = new HashMap<>();

        // Inserting elements
        sparseArray.put(0, "Apple");
        sparseArray.put(2, "Banana");
        sparseArray.put(4, "Orange");

        // Accessing elements
        System.out.println(sparseArray.get(0)); // Output: Apple
        System.out.println(sparseArray.get(1)); // Output: null
        System.out.println(sparseArray.get(2)); // Output: Banana
        System.out.println(sparseArray.get(3)); // Output: null
        System.out.println(sparseArray.get(4)); // Output: Orange

        // Checking if an index exists
        System.out.println(sparseArray.containsKey(0)); // Output: true
        System.out.println(sparseArray.containsKey(1)); // Output: false
        System.out.println(sparseArray.containsKey(2)); // Output: true

        // Removing elements
        sparseArray.remove(2);
        System.out.println(sparseArray.containsKey(2)); // Output: false
    }
}

In the example above, we create a HashMap called sparseArray to store the sparse array. We then insert elements at specific indices using the put method. We can access elements using the get method by providing the desired index. If an index doesn’t exist, the method will return null.

To check if an index exists in the sparse array, we use the containsKey method. We can also remove elements by using the remove method, passing the index as an argument.

Using a HashMap (or any other Map implementation) for sparse arrays provides fast access to elements by index, reduces memory usage, and avoids the need to store default values for non-existent elements.

By using sparse arrays, we can optimize our code and save memory when dealing with large arrays that contain mostly empty elements.

#java #sparsearray