public static void main(String[] args)    {        List
     
       list = new ArrayList
      
       ();        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
      
        list = new ArrayList
       
        ();        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
        
         > map = new HashMap
         
          >();        for (Student s : list) {            if (map.containsKey(s.getName())) {                List
          
            rList = map.get(s.getName());                rList.add(s.getId());            } else {                List
           
             rList = new ArrayList
            
             (); rList.add(s.getId()); map.put(s.getName(), rList); } } System.out.println(map.toString()); }}