MaxHeap.java

public class MaxHeap {
    public static void main(String[] args){
        maxHeap heap = new maxHeap(20);
        heap.insert(5);
        heap.insert(3);
        heap.insert(17);
        heap.insert(10);
        heap.insert(84);
        heap.insert(19);

        System.out.println("Max: " + heap.extractMax());  //Should print 84 as the max.
    }
    public static class maxHeap{
        int[] heap;
        int size;
        int capacity;

        public maxHeap(int capacity){
            this.capacity = capacity;
            this.heap = new int[capacity];
            this.size = 0;
        }

        private int parent(int i) { return((i - 1) / 2);}
        private int left(int i) {return(2 * i + 1);}
        private int right(int i) {return(2 * i + 2);}

        public void insert(int data){
            if(size == capacity){
                System.out.println("Heap is Full!");
                return;
            }
            heap[size] = data;
            heapifyUp(size);
            size++;
        }
        public int extractMax(){
            if(size == 0){
                System.out.println("Heap is Empty!");
            };
            int max = heap[0];
            heap[0] = heap[size -1];
            size--;
            heapifyDown(0);
            return max;
        }
        private void heapifyUp(int i){
            while(i > 0 && heap[parent(i)] < heap[i]){
                swap(parent(i), i);
                i = parent(i);
            }
        }
        private void heapifyDown(int i){
            int largest = i;
            int l = left(i);
            int r = right(i);

            if(l < size && heap[l] > heap[largest]) largest = l;
            if(r < size && heap[r] > heap[largest]) largest = r;

            if(largest != i){
                swap(i, largest);
                heapifyDown(largest);
            }
        }
        private void swap(int i, int j){
            int temp = heap[i];
            heap[i] = heap[j];
            heap[j] = temp;
        }
    }
}