public static int BF(String str,String sub) {
        if(str==null || sub==null) {
            return -1;
        }
        int lenStr=str.length();
        int lenSub=sub.length();
        if(lenStr==0 || lenSub==0) {
            return -1;
        }
        int i=0;
        int j=0;
        while(i<lenStr && j<lenSub) {
            if(str.charAt(i)==sub.charAt(j)) {
                i++;
                j++;
            }else {
                i=i-j+1;
                j=0;
            }
        }
        if(j>=lenSub) {//注意 =
            return i-j;
        }
        return -1;
    }
    public static void main1(String[] args) {
        System.out.println(BF("kdjfoeiaw","jfoe"));//2
        System.out.println(BF("kdjfoeiaw","kdjf"));//0
        System.out.println(BF("kdjfoeiaw","jfoeo"));//-1

    }
}