public class 快速排序 {
    public static void main(String[] args) {
        int[] arr = new int[]{5, 2, 9, 6, 22, 21};
        //System.out.println(Arrays.toString(kuaiPai(arr)));
       //  System.out.println(Arrays.asList("dada", "dda", "ddd"));
        //System.out.println(String.join(",", Arrays.asList("dada", "dda", "ddd")));
        String s="adjj";
        //第一种方法用substring来解决
        System.out.println(s.substring(0, 1).toUpperCase() + s.substring(1));
        //第二种方法用replace来解决
        String replace = s.replace(String.valueOf(s.charAt(0)), String.valueOf(s.charAt(0)).toUpperCase());
        System.out.println(replace);
    }