Simple way to compare 2 ArrayLists

Question

I have 2 arraylists of string object   List lt String gt  sourceList   new ArrayList lt String gt     List lt String gt  destinationList   new ArrayList lt String gt       I have some logic where i need to process the source list and will end up with the destination list  The destination list will have some additional elements added to the source list or removed from source list   My expected output is 2 ArrayList of string where the first list should have all the strings removed from the source and second list should have all the strings newly added to the source   Any simpler method to achieve this

User · Answer

If your requirement is to maintain the insertion order plus check the contents of the two arraylist then you should do following:

List<String> listOne = new ArrayList<String>();
List<String> listTwo = new ArrayList<String>();

listOne.add("stack");
listOne.add("overflow");

listTwo.add("stack");
listTwo.add("overflow");

boolean result = Arrays.equals(listOne.toArray(),listTwo.toArray());

This will return true.

However, if you change the ordering for example:

listOne.add("stack");
listOne.add("overflow");

listTwo.add("overflow");
listTwo.add("stack");

boolean result = Arrays.equals(listOne.toArray(),listTwo.toArray());

will return false as ordering is different.

User · Answer

This should check if two lists are equal  it does some basic checks first  i e  nulls and lengths   then sorts and uses the collections equals method to check if they are equal   public  boolean equalLists List lt String gt  a  List lt String gt  b               Check for sizes and nulls      if  a    null  amp  amp  b    null  return true        if   a    null  amp  amp  b   null      a    null  amp  amp  b   null      a size      b size                   return false                Sort and compare the two lists               Collections sort a       Collections sort b             return a equals b

User · Answer

private int compareLists List lt String gt  list1  List lt String gt  list2       Collections sort list1       Collections sort list2        int maxIteration   0      if list1 size      list2 size      list1 size    lt  list2 size             maxIteration   list1 size          else           maxIteration   list2 size               for  int index   0  index  lt  maxIteration  index              int result   list1 get index  compareTo list2 get index            if  result    0                continue            else               return result                      return list1 size   - list2 size

User · Answer

As far as I understand it correctly  I think it s easiest to work with 4 lists   - Your sourceList  - Your destinationList  - A removedItemsList  - A newlyAddedItemsList

User · Answer

Convert the List in to String and check whether the Strings are same or not  import java util ArrayList  import java util List             author Rakesh KR        public class ListCompare        public static boolean compareList List ls1 List ls2           return ls1 toString   contentEquals ls2 toString    true false            public static void main String   args             ArrayList lt String gt  one    new ArrayList lt String gt             ArrayList lt String gt  two    new ArrayList lt String gt              one add  one            one add  two            one add  six             two add  one            two add  two            two add  six             System out println  Output1      compareList one two             two add  ten             System out println  Output2      compareList one two

User · Answer

Convert Lists to  Collection and use removeAll      Collection lt String gt  listOne   new ArrayList Arrays asList  a   b    c    d    e    f    g         Collection lt String gt  listTwo   new ArrayList Arrays asList  a   b     d    e    f    gg    h           List lt String gt  sourceList   new ArrayList lt String gt  listOne       List lt String gt  destinationList   new ArrayList lt String gt  listTwo         sourceList removeAll  listTwo        destinationList removeAll  listOne           System out println  sourceList        System out println  destinationList      Output    c  g   gg  h     EDIT   other way  more clear     Collection lt String gt  list   new ArrayList Arrays asList  a   b    c    d    e    f    g          List lt String gt  sourceList   new ArrayList lt String gt  list       List lt String gt  destinationList   new ArrayList lt String gt  list        list add  boo        list remove  b         sourceList removeAll  list        list removeAll  destinationList          System out println  sourceList        System out println  list      Output    b   boo

User · Answer

List lt String gt  oldList   Arrays asList  a    b    c    d    e    f    List lt String gt  modifiedList   Arrays asList  a    b    c    d    e    g     List lt String gt  added   new HashSet lt  gt  modifiedList   List lt String gt  removed   new HashSet lt  gt  oldList    modifiedList stream   filter removed  remove  forEach added  remove       added items System out println added      removed items System out println removed

User · Answer

The simplest way is to iterate through source and destination lists one by one like this   List lt String gt  newAddedElementsList   new ArrayList lt String gt     List lt String gt  removedElementsList   new ArrayList lt String gt     for String ele   sourceList       if destinationList contains ele            continue       else          removedElementsList add ele           for String ele   destinationList       if sourceList contains ele            continue       else          newAddedElementsList add ele             Though it might not be very efficient if your source and destination lists have many elements but surely its simpler

User · Answer

boolean isEquals List lt String gt  firstList  List lt String gt  secondList       ArrayList lt String gt  commons   new ArrayList lt  gt          for  String s2   secondList            for  String s1   firstList               if s2 contains s1                   commons add s2                                     firstList removeAll commons       secondList removeAll commons       return   firstList size    gt  0    secondList size    gt  0

User · Answer

The answer is given in  dku-rajkumar post   ArrayList commonList   CollectionUtils retainAll list1 list2

[java] Simple way to compare 2 ArrayLists

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