List difference in java

I have two ArrayList<Integer> as follows:

original: 12, 16, 17, 19, 101

selected: 16, 19, 107, 108, 109

I want to do difference on these lists such that in the end I have two lists:

Add: 108,109,107

remove: 12, 17, 101

Length of original and selected lists varies and one can be greater/smaller than the other

Solution 1:

As an alternative, you could use CollectionUtils from Apache commons library. It has static intersection, union and subtract methods suitable for your case.

Solution 2:

List<Integer> original = Arrays.asList(12,16,17,19,101);
List<Integer> selected = Arrays.asList(16,19,107,108,109);

ArrayList<Integer> add = new ArrayList<Integer>(selected);
add.removeAll(original);
System.out.println("Add: " + add);

ArrayList<Integer> remove = new ArrayList<Integer>(original);
remove.removeAll(selected);
System.out.println("Remove: " + remove);

Output:

Add: [107, 108, 109]
Remove: [12, 17, 101]

Uses Collection's removeAll method. See javadocs.

Solution 3:

Intersection: original.retainAll(selected).

After that original will contain only elements present in both collections. Returns true if anything changed.

WARNING: This method is very slow for large collections

Solution 4:

For intersection and union operations the natural collection type is a Set rather than a List, its also more efficient to use.

Solution 5:

Using Guava library:

List<Integer> listA = Lists.newArrayList(12,16,17,19,101);
List<Integer> listB = Lists.newArrayList(16,19,107,108,109);
Set<Integer> intersection = Sets.intersection(Sets.newHashSet(listA), Sets.newHashSet(listB));
listA.removeAll(intersection);
listB.removeAll(intersection);