Java排列组合字符串的方法

import org.junit.Test;import java.util.ArrayList;import java.util.HashSet;import java.util.List;public class test2 {  @Test  public void test3() {    String input="abc";    //1.开始排列    List<String> sortResult = sort(input);    System.out.println("排列组合,字符串:"+input);    //2.消除重复列    HashSet h = new HashSet(sortResult);    sortResult.clear();    sortResult.addAll(h);    //3.打印输出    sortResult.forEach(e -> System.out.println(e));    //4.打印个数    System.out.println("排列组合个数：" + sortResult.size());  }  private List<String> sort(String input) {    List<String> sortList = new ArrayList();    if (input == null || "".equals(input)) {      System.out.println("提示：您输入了空字符,请输入有效值！");      return new ArrayList();    }    char leftChar = input.charAt(0);    if (input.length() > 1) {      String rightString = input.substring(1, input.length());      List<String> rightStringSortedList = sort(rightString);      rightStringSortedList.forEach((e) -> {        for (int i = 0; i < e.length() + 1; i++) {          sortList.add(new StringBuffer(e).insert(i, leftChar).toString());        }      });    } else {      sortList.add(String.valueOf(leftChar));    }    return sortList;  }}