java字符串排列组合

要生成Java字符串的排列组合，可以使用递归的方法。

以下是一个示例代码，可以输出字符串的所有排列组合：

import java.util.HashSet;
import java.util.Set;

public class Permutations {
    public static Set<String> generatePermutations(String str) {
        Set<String> set = new HashSet<>();
        if (str == null) {
            return set;
        } else if (str.length() == 0) {
            set.add("");
            return set;
        }

        char firstChar = str.charAt(0);
        String remainingStr = str.substring(1);
        Set<String> permutations = generatePermutations(remainingStr);
        for (String permutation : permutations) {
            for (int i = 0; i <= permutation.length(); i++) {
                set.add(insertCharAt(permutation, firstChar, i));
            }
        }
        return set;
    }

    private static String insertCharAt(String str, char c, int index) {
        String start = str.substring(0, index);
        String end = str.substring(index);
        return start + c + end;
    }

    public static void main(String[] args) {
        Set<String> permutations = generatePermutations("abc");
        for (String permutation : permutations) {
            System.out.println(permutation);
        }
    }
}

输出结果为：

acb
cab
bac
cba
bca
abc