字符串无法工作的Java插入排序方法

public class InsertionSort {
    public static void insertionSort(String[] arr) {
        int n = arr.length;
        for (int i = 1; i < n; ++i) {
            String key = arr[i];
            int j = i - 1;

            while (j >= 0 && arr[j].compareTo(key) > 0) {
                arr[j + 1] = arr[j];
                j = j - 1;
            }
            arr[j + 1] = key;
        }
    }

    public static void main(String[] args) {
        String[] arr = {"apple", "banana", "orange", "grape", "kiwi"};
        insertionSort(arr);
        for (String s : arr) {
            System.out.print(s + " ");
        }
    }
}