这里有一个不影响列表排序的方法:

ArrayList l1 = new ArrayList();
ArrayList l2 = new ArrayList();

Iterator iterator = l1.iterator();

while (iterator.hasNext()) {
    YourClass o = (YourClass) iterator.next();
    if(!l2.contains(o)) l2.add(o);
}

L1是原始列表，l2是没有重复项的列表 (确保你的类有equals方法，根据你想要代表的相等)

@jonathan-stafford的解决方案是可以的。但这并没有保持列表的顺序。

如果你想保留列表的顺序，你必须使用这个:

public static <T> void removeDuplicate(List <T> list) {
Set <T> set = new HashSet <T>();
List <T> newList = new ArrayList <T>();
for (Iterator <T>iter = list.iterator();    iter.hasNext(); ) {
   Object element = iter.next();
   if (set.add((T) element))
      newList.add((T) element);
   }
   list.clear();
   list.addAll(newList);
}

这只是为了完成答案。很好!

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);
        }


    }
}

还有来自Guava的ImmutableSet作为一个选项(这里是文档):

ImmutableSet.copyOf(list);

public static void main(String[] args){
    ArrayList<Object> al = new ArrayList<Object>();
    al.add("abc");
    al.add('a');
    al.add('b');
    al.add('a');
    al.add("abc");
    al.add(10.3);
    al.add('c');
    al.add(10);
    al.add("abc");
    al.add(10);
    System.out.println("Before Duplicate Remove:"+al);
    for(int i=0;i<al.size();i++){
        for(int j=i+1;j<al.size();j++){
            if(al.get(i).equals(al.get(j))){
                al.remove(j);
                j--;
            }
        }
    }
    System.out.println("After Removing duplicate:"+al);
}

代码:

List<String> duplicatList = new ArrayList<String>();
duplicatList = Arrays.asList("AA","BB","CC","DD","DD","EE","AA","FF");
//above AA and DD are duplicate
Set<String> uniqueList = new HashSet<String>(duplicatList);
duplicatList = new ArrayList<String>(uniqueList); //let GC will doing free memory
System.out.println("Removed Duplicate : "+duplicatList);

注意:肯定会有内存开销。