java 输入一个长度为 n 由大小写字母组成的字符串，打印出该字符串中字符的所有排列

您可以使用递归的方式来实现字符串中字符的所有排列。下面是一个示例代码：

import java.util.*;

public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.print("请输入一个字符串：");
        String str = scanner.nextLine();
        List<String> permutations = findPermutations(str);
        System.out.println("字符串中字符的所有排列为：");
        for (String permutation : permutations) {
            System.out.println(permutation);
        }
    }
  
    public static List<String> findPermutations(String str) {
        List<String> permutations = new ArrayList<>();
        if (str == null || str.length() == 0) {
            return permutations;
        }
        char[] chars = str.toCharArray();
        boolean[] visited = new boolean[chars.length];
        StringBuilder sb = new StringBuilder();
        backtrack(chars, visited, sb, permutations);
        return permutations;
    }

    private static void backtrack(char[] chars, boolean[] visited, StringBuilder sb, List<String> permutations) {
        if (sb.length() == chars.length) {
            permutations.add(sb.toString());
            return;
        }
        for (int i = 0; i < chars.length; i++) {
            if (visited[i]) {
                continue;
            }
            visited[i] = true;
            sb.append(chars[i]);
            backtrack(chars, visited, sb, permutations);
            sb.deleteCharAt(sb.length() - 1);
            visited[i] = false;
        }
    }
}

运行这段代码后，您可以输入一个长度为n的由大小写字母组成的字符串。程序将会打印出该字符串中字符的所有排列。

注意：该算法的时间复杂度为O(n!)，当n较大时，可能会消耗较长的时间和内存。