I have two list string different,
List<String> A= [1,2,3,4]; List<String> B= [1,2,5,6]; And I want to combine two list, in new list string in List C = new Arraylist ();
how to combine two list string , be like the example:
C = [1,2,3,4,5,6]; 
- 1A.addAll(B) will add all B elements to ASubin Sebastian– Subin Sebastian2012-12-24 09:57:24 +00:00Commented Dec 24, 2012 at 9:57
- Use a Set implementation for merge without duplicationKiran Mohan– Kiran Mohan2012-12-24 10:01:04 +00:00Commented Dec 24, 2012 at 10:01
- If you got the answer then accept that and if you are still not found desire answer then please paste your problem including exception if it is.Rais Alam– Rais Alam2012-12-24 10:26:34 +00:00Commented Dec 24, 2012 at 10:26
- How to reach this result: C = [1,2] - only unique items?Roman Soviak– Roman Soviak2019-02-17 22:25:28 +00:00Commented Feb 17, 2019 at 22:25
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8 Answers
Use Collection.addAll(), and a TreeSet, to remove duplicates and keep the result sorted.
Set<String> c = new TreeSet<String>(a); //create a Set with all the elements in a c.addAll(b); //add all the elements in b answered Dec 24, 2012 at 9:57
Aleksander Blomskøld
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Comments
This will get them combined
combined = new ArrayList<String>(); combined.addAll(A); combined.addAll(B); This will get the uniques
List<String> uniques = new ArrayList<String>(new HashSet<String>(combined)); 
Comments
Do it like this :
listOne.removeAll(listTwo); listTwo.addAll(listOne); Collections.sort(listTwo); You can remove the third line if you do not want it to be sorted.
2 Comments
Kiran Mohan
this is better but only if original lists can be modified.
Abhishek_Mishra
If you want the first list not to be modified then you can store it in a temporary list.A very common coding scheme:)
Declaration of A and B seems to be wrong.
However, given two lists A and B, to combine them into C, you can use the following code: C.addAll(A); C.addAll(B);
Comments
Set<String> set = new TreeSet<String>(A); // for keeping the output sorted else you can also use java.util.HashSet set.addAll(B); List<String> finalList = new ArrayList<String>(set); 
Comments
There are two ways to merge the results of both lists: using List#addAll or Set#addAll. The main difference between both is heavily explained here: What is the difference between Set and List?
Based on your request, you should merge both lists without repeating the items using a Set
List<String> lstA = new ArrayList<String>(); lstA.add("1"); lstA.add("2"); lstA.add("3"); lstA.add("4"); List<String> lstB = new ArrayList<String>(); lstA.add("1"); lstA.add("2"); lstA.add("5"); lstA.add("6"); Set<String> lstC = new LinkedHashSet<String>(); lstC.addAll(A); lstC.addAll(B); List<String> lstAB = new ArrayList(lstC); 
Comments
List<String> A= new ArrayList<String>(); List<String> B= new ArrayList<String>(); Set<String> set = new TreeSet<String>(A); set.addAll(B); System.out.println(new ArrayList<String>(set)); 
1 Comment
Luiggi Mendoza
TreeSet maintains the data sorted, not ordered. LinkedHashSet maintains the data ordered but not sorted.To get a List<String> in sorted order, use this piece of code
String a[] = {"1","2","3","4"}; String b[] = {"1","2","5","6"}; List<String> A= Arrays.asList(a); List<String> B= Arrays.asList(b); Set<String> CTemp = new TreeSet<>(); CTemp.addAll(A); CTemp.addAll(B); List<String> C = new ArrayList<>(CTemp); 