向下调整建小根堆的Java代码

下面是建立小根堆的Java代码示例：

public class MinHeap {

    private int[] heap;
    private int size;
    private int capacity;

    public MinHeap(int capacity) {
        this.capacity = capacity;
        this.size = 0;
        this.heap = new int[capacity + 1];
    }

    public void insert(int value) {
        if (size >= capacity) {
            return;
        }

        size++;
        int index = size;
        heap[index] = value;

        while (index > 1 && heap[index] < heap[index / 2]) {
            swap(index, index / 2);
            index = index / 2;
        }
    }

    public void heapify(int index) {
        int smallest = index;
        int left = 2 * index;
        int right = 2 * index + 1;

        if (left <= size && heap[left] < heap[smallest]) {
            smallest = left;
        }

        if (right <= size && heap[right] < heap[smallest]) {
            smallest = right;
        }

        if (smallest != index) {
            swap(index, smallest);
            heapify(smallest);
        }
    }

    public int extractMin() {
        if (size == 0) {
            return -1;
        }

        int min = heap[1];
        heap[1] = heap[size];
        size--;

        heapify(1);

        return min;
    }

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