利用了Set不重复的特性

方法一：

public static List removeDuplicateWithOrder(List list) {
        Set set = new HashSet();
        List newList = new ArrayList();
        for (Iterator iter = list.iterator(); iter.hasNext();) {
            Object element = iter.next();
            if (set.add(element))
                newList.add(element);
        }
        return newList;
    } 

方法二：

public static List<String> removeDuplicate(List<String> list)
{
       Set set = new LinkedHashSet<String>();
        set.addAll(list);
        list.clear();
        list.addAll(set);
        return list;
} 

方法三：

import java.util.*; 
class sigleE 
{
	public static void main(String[] args) 
	{
		ArrayList al = new ArrayList();
		al.add("java1");
		al.add("java2");
		al.add("java1");
		al.add("java3");
		System.out.println(al);
		al = list(al);
		System.out.println(al);
	}
	public static ArrayList list(ArrayList al)
	{
		ArrayList newal = new ArrayList();//新建一个中间集合
		for(Iterator it = al.iterator();it.hasNext();)//集合循环
		{
			Object obj = it.next();
			if(!newal.contains(obj))//不包含重复的输出
				newal.add(obj);
		}
		return newal;
	}
}