Java: check if array is heap

Perhaps this is what you want:

public static void main(String... args) {
    int[] A = {50, 45, 40, 35, 20, 25, 20};
    int[] B = {45, 50, 40, 35, 20, 25, 20};
    System.out.println(isMaxHeap(A));
    System.out.println(isMaxHeap(B));
}

private static boolean isMaxHeap(int[] arr) {
    int N = arr.length;
    for (int i = (N - 2) / 2; i > -1; --i) { // start from the first internal node who has children;
        int j = 2 * i + 1; // the left child;
        if (j < N - 1 && arr[i] < arr[j+1]) j++; // select the bigger child;
        if (arr[i] < arr[j]) return false; // if parent is smaller than the child;
    }
    return true;
}

But do please show some efforts next time before asking.