Java Compare Two List s object values

Question

I have two list   ListA lt MyData gt  listA   new ArrayList lt MyData gt      and ListB lt MyData gt  listB   new ArrayList lt MyData gt    both contain object of type MyData and MyData contain these variables   MyData       String name      boolean check       ListA and ListB both contains MyData objects  now I have to compare both the list s object values here name as well check variable like if ListA contains these object values   ListA     Ram  true    Hariom  true    Shiv  true     and ListB also contain   ListB     Ram  true    Hariom  true    Shiv  true     then i have to compare lists and return false because both list are same  But if ListA contains  ListA     Ram  true    Hariom  true    Shiv  false     and ListB Contain   ListB     Ram  true    Hariom  true    Shiv  true     then I have to compare lists and return true because both list are not same   or vice-versa so any slight change in the any list values I have to return true  One thing I have to mentioned here objects can be in any order

User · Answer

String myData1   list1 toString    String myData2   list2 toString    return myData1 equals myData2    where   list1 - List lt MyData gt  list2 - List lt MyData gt    Comparing the String worked for me  Also NOTE I had overridden toString   method in MyData class

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Logic should be something like    First step  For class MyData implements Comparable interface  override the compareTo method as per the per object requirement  Second step  When it comes to list comparison  after checking for nulls    2 1 Check the size of both lists  if equal returns true else return false  continue to object iteration 2 2 If step 2 1 returns true  iterate over elements from both lists and invoke something like    listA get i  compareTo listB get i     This will be as per the code mentioned in step-1

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It s been about 5 years since then and luckily we have Kotlin now  Comparing of two lists now looks is as simple as   fun areListsEqual list1   List lt Any gt   list2   List lt Any gt     Boolean           return list1    list2     Or just feel free to omit it at all and use equality operator

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I found a very basic example of List comparison at List Compare This example verifies the size first and then checks the availability of the particular element of one list in another

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First  implement the MyData equals Object o  and MyData hashCode   methods  Once you implemented the equals method  you can iterate over the lists as follows   if ListA    null  amp  amp  ListB    null      return false  if ListA    null  amp  amp  ListB    null      return true  if ListA    null  amp  amp  ListB    null      return true  int max   ListA size    gt  ListB size     ListA size     ListB size    for int i   0  i  lt  max  i          myData1   ListA get i       myData2   ListB get i       if  myData1 equals myData2             return true          return false

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See if this works   import java util ArrayList  import java util List    public class ArrayListComparison        public static void main String   args            List lt MyData gt  list1   new ArrayList lt MyData gt             list1 add new MyData  Ram   true            list1 add new MyData  Hariom   true            list1 add new MyData  Shiv   true            list1 add new MyData  Shiv   false            List lt MyData gt  list2   new ArrayList lt MyData gt             list2 add new MyData  Ram   true            list2 add new MyData  Hariom   true            list2 add new MyData  Shiv   true             System out println  Lists are equal     listEquals list1  list2               private static boolean listEquals List lt MyData gt  list1  List lt MyData gt  list2            if list1 size      list2 size                return true          for  MyData myData   list1                if  list2 contains myData                   return true                    return false           class MyData      String name      boolean check        public MyData String name  boolean check            super            this name   name          this check   check             Override     public int hashCode             final int prime   31          int result   1          result   prime   result    check   1231   1237           result   prime   result     name    null    0   name hashCode             return result             Override     public boolean equals Object obj            if  this    obj              return true          if  obj    null              return false          if  getClass      obj getClass                return false          MyData other    MyData  obj          if  check    other check              return false          if  name    null                if  other name    null                  return false            else if   name equals other name               return false          return true

User · Answer

ArrayList already have support for this  with the equals method  Quoting the docs           In other words  two lists are defined to be equal if they contain the same elements in the same order    It does require you to properly implement equals in your MyData class   Edit   You have updated the question stating that the lists could have different orders  In that case  sort your list first  and then apply equals

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Using java 8 removeIf to compare similar items  public int getSimilarItems        List lt String gt  one   Arrays asList  milan    dingo    elpha    hafil    meat    iga    neeta peeta        List lt String gt  two   new ArrayList lt  gt  Arrays asList  hafil    iga    binga    mike    dingo       Cannot remove directly from array backed collection     int initial   two size         two removeIf one  contains       return initial - two size

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You can subtract one list from the other using CollectionUtils subtract  if the result is an empty collection  it means both lists are the same  Another approach is using CollectionUtils isSubCollection or CollectionUtils isProperSubCollection   For any case you should implement equals and hashCode methods for your object

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I think you can sort both lists and convert to List if some of them was a HashSet colleciton   java utils Collections package lets you do it   List lt Category gt  categoriesList   new ArrayList lt  gt     Set lt Category gt  setList   new HashSet lt  gt     Collections sort categoriesList   List lt Category gt  fileCategories   new ArrayList lt  gt  setList   Collections sort fileCategories    if categoriesList size      fileCategories size    amp  amp  categoriesList containsAll fileCategories           Do something

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It s not the most efficient solution but the most terse code would be   boolean equalLists   listA size      listB size    amp  amp  listA containsAll listB     Update    WesleyPorter is right  The solution above will not work if duplicate objects are in the collection  For a complete solution you need to iterate over a collection so duplicate objects are handled correctly   private static boolean cmp  List lt   gt  l1  List lt   gt  l2            make a copy of the list so the original list is not changed  and remove   is supported     ArrayList lt   gt  cp   new ArrayList lt  gt   l1        for   Object o   l2             if    cp remove  o                   return false                      return cp isEmpty        Update 28-Oct-2014    RoeeGavriel is right  The return statement needs to be conditional  The code above is updated

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I know it s old question but in case anyone needs it  I use this in my application and it works well  i used it to check if the cart has been changed or not     private boolean validateOrderProducts Cart cart        boolean doesProductsChanged   false      if  originalProductsList size      cart getCartItemsList   size              for  Product originalProduct   originalProductsList                if   doesProductsChanged                    for  Product cartProduct   cart getCartProducts                          if  originalProduct getId      cartProduct getId                              if  originalProduct getPivot   getProductCount      cartProduct getCount                                  doesProductsChanged   true                                 cart has been changed - gt  break from inner loop                             break                                                  else                           doesProductsChanged   false                                                        else                      cart is already changed - gt  break from first loop                 break                                else              some products has been added or removed  simplest case of Change          return true            return doesProductsChanged

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This can be done easily through Java8 using forEach and removeIf method   Take two lists  Iterate from listA and compare elements inside listB  Write any condition inside removeIf method   Hope this will help  listToCompareFrom forEach entity - gt  listToRemoveFrom removeIf x - gt  x contains entity

User · Answer

Override the equals method in your class and use  Collection equals   method to check for equality

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I got this solution for above problem   public boolean compareLists List lt MyData gt  prevList  List lt MyData gt  modelList            if  prevList size      modelList size                  for  MyData modelListdata   modelList                    for  MyData prevListdata   prevList                        if  prevListdata getName   equals modelListdata getName                                 amp  amp  prevListdata isCheck      modelListdata isCheck                              return  true                                                                            else              return true                    return false            EDITED -  How can we cover this    Imagine if you had two arrays  A  true  B  true  C  true and  A  true  B  true  D  true  Even though array one has C and array two has D there s no check that will catch that Mentioned by  Patashu   SO for that i have made below changes   public boolean compareLists List lt MyData gt  prevList  List lt MyData gt  modelList            if  prevList   null  amp  amp  modelList  null  amp  amp  prevList size      modelList size                  boolean indicator   false              for  MyData modelListdata   modelList                    for  MyData prevListdata   prevList                        if  prevListdata getName   equals modelListdata getName                                 amp  amp  prevListdata isCheck      modelListdata isCheck                              return  true                                             if  modelListdata getName   equals prevListdata getName                               indicator   false                          break                        else                         indicator   true                                                             if  indicator              return true                          else              return true                    return false

[java] Java Compare Two List's object values?

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