二分查找

long[] a = {1, 2, 3, 4, 7, 3, 5, 10, 23, 89, 44};
int i = binarySearch(a, 4);
System.out.println(i);

public static int binarySearch(long[] a, long key) {

    int low = 0;
    int high = a.length - 1;

    while (low <= high) {
        int mid = (low + high) >>> 1;
        long midVal = a[mid];

        if (midVal < key) {
            low = mid + 1;
        } else if (midVal > key) {
            high = mid - 1;
        } else {
            return mid;
        }
    }
    return -1;
}