public Set<Object> findDuplicates(List<Object> list) {
        Set<Object> items = new HashSet<Object>();
        Set<Object> duplicates = new HashSet<Object>();
        for (Object item : list) {
            if (items.contains(item)) {
                duplicates.add(item);
                } else { 
                    items.add(item);
                    } 
            } 
        return duplicates;
        }

你可以在下面使用嵌套循环:

ArrayList<Class1> l1 = new ArrayList<Class1>();
ArrayList<Class1> l2 = new ArrayList<Class1>();

        Iterator iterator1 = l1.iterator();
        boolean repeated = false;

        while (iterator1.hasNext())
        {
            Class1 c1 = (Class1) iterator1.next();
            for (Class1 _c: l2) {
                if(_c.getId() == c1.getId())
                    repeated = true;
            }
            if(!repeated)
                l2.add(c1);
        }

import java.util.*;
class RemoveDupFrmString
{
    public static void main(String[] args)
    {

        String s="appsc";

        Set<Character> unique = new LinkedHashSet<Character> ();

        for(char c : s.toCharArray()) {

            System.out.println(unique.add(c));
        }
        for(char dis:unique){
            System.out.println(dis);
        }


    }
}

用于自定义对象列表

   public List<Contact> removeDuplicates(List<Contact> list) {
    // Set set1 = new LinkedHashSet(list);
    Set set = new TreeSet(new Comparator() {

        @Override
        public int compare(Object o1, Object o2) {
            if (((Contact) o1).getId().equalsIgnoreCase(((Contact) o2).getId()) /*&&
                    ((Contact)o1).getName().equalsIgnoreCase(((Contact)o2).getName())*/) {
                return 0;
            }
            return 1;
        }
    });
    set.addAll(list);

    final List newList = new ArrayList(set);
    return newList;
}

Set<String> strSet = strList.stream().collect(Collectors.toSet());

是删除副本的最简单方法。

你也可以这样做，保持秩序:

// delete duplicates (if any) from 'myArrayList'
myArrayList = new ArrayList<String>(new LinkedHashSet<String>(myArrayList));