Comparing two ArrayList

[Joe San]

Guys,

I want to compare two ArrayLists and extract the values that do not match. How could I do this? The ArrayList simply containes numbers.

[Campbell Ritchie]

Are you supposed to do it the proper way with the methods of the List interfaceor are you supposed to do it the hard way by iterating through both Lists?

[Campbell Ritchie]

Follow the method links from List to Collection, then to Set, that might give better hints what they are supposed to do.

[Joe San]

I have two Lists, one is big (with a max of 10 elements) and one is small which can be either equal or less than the other List. I want to compare both these Lists and get the ones that do not match.

[Balu Sadhasivam]

Jothi,

Add your first list to a Set. Then add each object from second list to the same set. If it already exists "add()" method would return false . If its false add it to a temporary array !!

[Rob Spoor]

Perhaps you can play around with the bulk operators: addAll, removeAll and retainAll. You may need to use some extra collections for that to work, because these methods modify the original.

[Campbell Ritchie]

Now Rob has hinted about three methods . . .

Close examination of the corresponding methods in the java.util.Set interface will give some very useful information.

[Prasad Kumbhare]

I would do it using , contains method. Some steps would be

1) using iterator traverse through second list which has less elements
2) get next element from second list
3) use contains method to check if that element exists in first list which is big one. If no then add it into temp list
4) Once loop got executed your temp list will have elements from second list which are not there from first list.

I hope this helps.

Thanks

[Ganesh Gowtham]

Hi please use Collection Utils of Apache to do this Job .

  //import org.apache.commons.collections.CollectionUtils;
	List<Integer> firstList = new ArrayList<Integer>();
	firstList.add(1);
	firstList.add(2);
	firstList.add(3);
	firstList.add(4);
	List<Integer> secondList = new ArrayList<Integer>();
	secondList.add(1);
	secondList.add(2);
	secondList.add(5);
	Collection disJointList = CollectionUtils.disjunction(firstList, secondList);
	for (Object object : disJointList) {
		System.out.println(disJointList);
		//output is [4, 3, 5]
	}  

Hope this helps !!!

[Seetharaman Venkatasamy]

Rob Prime wrote:Perhaps you can play around with the bulk operators: addAll, removeAll and retainAll. You may need to use some extra collections for that to work, because these methods modify the original.

Really Good Hint . and i am wondering how you are point out exactly Everytime

[Rob Spoor]

Experience mostly, plus a pretty good knowledge of parts of the API.