Heap sort is a popular sorting algorithm that is used to sort elements in an array or list. The algorithm works by transforming the input list into a binary heap and then repeatedly removing the largest element and swapping it with the last element of the heap. This process is repeated until the entire list is sorted.

In this article, we will look at how to implement the heap sort algorithm in Java. The code for the heap sort program in Java is as follows:

public class HeapSort {
    public static void sort(int[] arr) {
        int n = arr.length;
 
        // Build heap (rearrange array)
        for (int i = n / 2 - 1; i >= 0; i--)
            heapify(arr, n, i);
 
        // One by one extract an element from heap
        for (int i=n-1; i>=0; i--) {
            // Move current root to end
            int temp = arr[0];
            arr[0] = arr[i];
            arr[i] = temp;
 
            // call max heapify on the reduced heap
            heapify(arr, i, 0);
        }
    }
 
    // To heapify a subtree rooted with node i which is
    // an index in arr[]. n is size of heap
    public static void heapify(int[] arr, int n, int i) {
        int largest = i; // Initialize largest as root
        int l = 2*i + 1; // left = 2*i + 1
        int r = 2*i + 2; // right = 2*i + 2
 
        // If left child is larger than root
        if (l < n && arr[l] > arr[largest])
            largest = l;
 
        // If right child is larger than largest so far
        if (r < n && arr[r] > arr[largest])
            largest = r;
 
        // If largest is not root
        if (largest != i) {
            int swap = arr[i];
            arr[i] = arr[largest];
            arr[largest] = swap;
 
            // Recursively heapify the affected sub-tree
            heapify(arr, n, largest);
        }
    }
 
    /* A utility function to print array of size n */
    public static void printArray(int[] arr) {
        int n = arr.length;
        for (int i=0; i<n; ++i)
            System.out.print(arr[i]+" ");
        System.out.println();
    }
 
    // Driver program
    public static void main(String args[]) {
        int[] arr = {12, 11, 13, 5, 6, 7};
        int n = arr.length;
 
        HeapSort ob = new HeapSort();
        ob.sort(arr);
 
        System.out.println("Sorted array is");
        printArray(arr);
    }
}

In the code above, the function sort takes an array of integers as input and uses the heapify function to sort the array. The heapify function takes three inputs: the array to be sorted, the size of the heap, and the root node.