删除LinkedList中的重复项

Question

I am a beginner in java. I have written the following code to find duplicates and remove them in a LinkedList but I am getting a ArrayIndexOutOfBounds Exception. please help. Thanks in advance.

    import java.util.*;
    public class LinkedListEx 
{
    public static void main(String[] args)
    {
        LinkedList<Integer> l1 = new LinkedList<Integer>();
        l1.add(1);
        l1.add(2);
        l1.add(1);
        l1.add(4);
        l1.add(1);
        System.out.println(l1);
        int i = l1.size();
        for(int j=0;j<i;j++)
        {
            for(int k=j+1;k<i;k++)
            {
                if(l1.get(j) == l1.get(k)){
                    l1.remove(k);
                }
            }
        }
    }
 }

Answer 1

Don't use get(int) on a LinkedList . It's fine on an ArrayList , but a LinkedList has to traverse the list to find the n'th element.

Use a Set to remember which values have already been seen, and iterate the list using an Iterator .

LinkedList<Integer> l1 = new LinkedList<Integer>();
l1.add(1);
l1.add(2);
l1.add(1);
l1.add(4);
l1.add(1);
System.out.println(l1);

HashSet<Integer> set = new HashSet<Integer>();
for (Iterator<Integer> iter = l1.iterator(); iter.hasNext(); ) {
    Integer value = iter.next();
    if (! set.add(value))
        iter.remove();
}
System.out.println(l1);

Output

[1, 2, 1, 4, 1]
[1, 2, 4]

Answer 2

Use Iterator to traverse through list when you are going to modify the list.

You are removing the items from list, which reduces the size of list but your loop still runs for initial size of list.

Answer 3

Try:

List<Integer> list = new LinkedList<>();
...

Set<Integer> set = new LinkedHashSet<>(list);
// either
list = new LinkedList<>(set);

// or
list.clear();
list.addAll(set);

With Java SE 8 you could also use:

list = list.stream().distinct().collect(Collectors.toCollection(LinkedList::new));

Or if it doesn't have to be a LinkedList (not very often needed in my experience):

list = list.stream().distinct().collect(Collectors.toList());

Answer 4

Your for loop should be more like this and also by updating your variable i :

int i = l1.size();
for(int j=0;j<i-1;j++) {
       for(int k=j+1;k<i;k++) {
           if(l1.get(j) == l1.get(k)) {
               l1.remove(k);
               i--; //Updated size
           }
       }
}