Java - Distinct List of Objects

Question

I have a list/collection of objects that may or may not have the same property values. What\'s the easiest way to get a distinct list of the objects with equal properties? I

Answer 1

Java 8:

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

See java.util.stream.Stream#distinct.

Answer 2

If you're using Eclipse Collections, you can use the method distinct().

ListIterable<Integer> integers = Lists.mutable.with(1, 3, 1, 2, 2, 1);
Assert.assertEquals(
    Lists.mutable.with(1, 3, 2),
    integers.distinct());

The advantage of using distinct() instead of converting to a Set and then back to a List is that distinct() preserves the order of the original List, retaining the first occurrence of each element. It's implemented by using both a Set and a List.

MutableSet<T> seenSoFar = Sets.mutable.with();
int size = list.size();
for (int i = 0; i < size; i++)
{
    T item = list.get(i);
    if (seenSoFar.add(item))
    {
        targetCollection.add(item);
    }
}
return targetCollection;

If you cannot convert your original List into an Eclipse Collections type, you can use ListAdapter to get the same API.

MutableList<Integer> distinct = ListAdapter.adapt(integers).distinct();

Note: I am a committer for Eclipse Collections.

Answer 3

Actually lambdaj implements this feature through the selectDistinctArgument method

http://lambdaj.googlecode.com/svn/trunk/html/apidocs/ch/lambdaj/Lambda.html#selectDistinctArgument(java.lang.Object,%20A)