java里有没有专门判断List里有重复的数据

public static void main(String[] args)

    {
        List<String> list = new ArrayList<String>();
        list.add("aa");
        list.add("bb");
        list.add("cc");
        list.add("dd");
        list.add("bb");
        list.add("ee");
        list.add("dd");
        list.add("ff");
          
        String temp = "";
        for (int i = 0; i < list.size() - 1; i++)
        {
            temp = list.get(i);
            for (int j = i + 1; j < list.size(); j++)
            {
                if (temp.equals(list.get(j)))
                {
                    System.out.println("第" + (i + 1) + "个跟第" + (j + 1) + "个重复，值是：" + temp);
                }
            }
        }
    }

 

package testCollection;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

import entity.Student;

public class ListRepeatData {
    public static void main(String[] args) {
        test();
    }

    public static void test() {
        List<Student> list = new ArrayList<Student>();
        Student s1 = new Student("1", "cxx1");
        Student s2 = new Student("2", "cxx2");
        Student s3 = new Student("3", "cxx1");
        Student s4 = new Student("4", "cxx2");
        Student s5 = new Student("5", "cxx1");
        Student s6 = new Student("6", "cxx2");
        Student s7 = new Student("7", "cxx3");
        list.add(s1);
        list.add(s2);
        list.add(s3);
        list.add(s4);
        list.add(s5);
        list.add(s6);
        list.add(s7);
        Map<String, List<String>> map = new HashMap<String, List<String>>();
        for (Student s : list) {
            if (map.containsKey(s.getName())) {
                List<String> rList = map.get(s.getName());
                rList.add(s.getId());
            } else {
                List<String> rList = new ArrayList<String>();
                rList.add(s.getId());
                map.put(s.getName(), rList);
            }
        }
        System.out.println(map.toString());
    }
}