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);}