String.indexOf()实现

public static void main(String[] args) { String haystack = "aaaaasdfasof"; String needle = "df"; char[] hs = haystack.toCharArray(); int hl = hs.length; char[] ns = needle.toCharArray(); int nl = ns.length; //haystack是空字符串时needle是空返回0否则-1 if (0 >= hl) { System