How to combine two list string into one list

Question

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];

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, Dec 24 '12 at 10:26

score 4 · Accepted Answer · answered Dec 24 '12 at 09:57

4

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 '12 at 09:57

Aleksander Blomskøld

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score 3 · Answer 2 · answered Dec 24 '12 at 09:58

3

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));

answered Dec 24 '12 at 09:58

maček

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score 3 · Answer 3 · answered Dec 24 '12 at 10:27

3

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.

answered Dec 24 '12 at 10:27

Abhishek_Mishra

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this is better but only if original lists can be modified. – Kiran Mohan Dec 24 '12 at 10:32
If you want the first list not to be modified then you can store it in a temporary list.A very common coding scheme:) – Abhishek_Mishra Dec 24 '12 at 10:36

score 0 · Answer 4 · edited May 23 '17 at 12:02

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);

score 0 · Answer 5 · answered Dec 24 '12 at 09:59

0

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);

answered Dec 24 '12 at 09:59

An Cong Tran

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Sandeep Pathak · Answer 6 · 2012-12-24T10:13:13.680

0

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));

edited Dec 24 '12 at 10:13

answered Dec 24 '12 at 10:00

Sandeep Pathak

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`TreeSet` maintains the data sorted, not ordered. `LinkedHashSet` maintains the data ordered but not sorted. – Luiggi Mendoza Dec 24 '12 at 10:03

score 0 · Answer 7 · answered Dec 24 '12 at 10:02

0

  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);

answered Dec 24 '12 at 10:02

Rahul

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Kiran Mohan · Answer 8 · 2012-12-24T10:29:44.013

0

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);

edited Dec 24 '12 at 10:29

answered Dec 24 '12 at 10:08

Kiran Mohan

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How to combine two list string into one list

8 Answers8