Java : Create new ArrayLists based on some condition from existing ArrayList

I am new to java .

I have 2 ArrayLists of Strings 

List<String> a= [2,14]
List<String> b= [2,3,4,5]

I want two new ArrayLists

1) List has the value which is in b but not in a

  List<String> c= [3,4,5]

2) List has the value a but not in b

  List<String> d=[14]

I tried:

    List<String> c = new ArrayList<String>(b);
    c.removeAll(a);
   System.out.println("c::::::::::::::::::::::::::::::"+c);  // 2,3,4,5

which is not removing the values of List a

Complete Code 

   public static void updatePartyType(List<String> oldPartyKeys, List<String> newPartyKeys, String customerCode) {
   System.out.println("oldPartyKeys--->"+oldPartyKeys);// 2,14
   System.out.println("newPartyKeys--->"+newPartyKeys); // 2,3,4,5

   System.out.println("oldPartyKeys class --->"+oldPartyKeys.getClass());// class java.util.ArrayList

   List<String> newlySelectedPartyKeys = new ArrayList<String>(newPartyKeys);
   newlySelectedPartyKeys.removeAll(oldPartyKeys);
                    System.out.println("newlySelectedPartyKeys::::::::::::::::::::::::::::"+newlySelectedPartyKeys);
Jon Skeet
people
quotationmark

You're really proposing set operations more than list operations - in which case you'd be better off using a HashSet than an ArrayList. Then you could use Collection<E>.removeAll:

Set<String> a = ...;
Set<String> b = ...;

Set<String> c = new HashSet<String>(b);
c.removeAll(a);

Set<String> d = new HashSet<String>(a);
d.removeAll(b);

(This will work for ArrayList as well as HashSet - I've only changed to using sets because it's a more appropriate type when you want set-based operations.)

Or better, use Guava's Sets.difference method:

Set<String> a = ...;
Set<String> b = ...;

Set<String> c = Sets.difference(b, a);
Set<String> d = Sets.difference(a, b);

This will create views on the differences - so changes to the original sets will be reflected in the views. You can effectively take a snapshot of a view by creating a new HashSet:

Set<String> snapshot = new HashSet<String>(c);

people

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