How to compare two Arraylists which contain objects of the same class in Java?

Question

I have 2 lists of different sizes which belong to the same class Officer which has attributes:

Integer id;
Integer level; 
String role;

I want to compare these two lists list1 and list2 so that I can generate two new lists insertLst and deleteList.

Both list 1 and list2 contain unique elements.

insertLst: This list contains items in list1 and not in list2.

deleteList: This list contains items in list2 and not in list1.

I have no idea how this should be done , might be using The org.apache.commons.collections.CollectionUtils API .

Could you suggest me a java code for generating these two lists insertLst and deleteList?

Make a copy of your original lists and use the removeAll() method on each list. Make sure that your class has overrided the equals() method. — Vasu
– Vasu, Commented Jun 6, 2013 at 11:09

Community · Accepted Answer · 2017-05-23 12:24:56Z

3

If you want to use org.apache.commons.collections.CollectionUtils then you should use subtract method.

Collection<Officer> insertList= CollectionUtils.subtract(list1, list2);
Collection<Officer> deleteList = CollectionUtils.subtract(list2, list1);

or you could write it like this (passing empty lists that are filled in method) not to add another library to your dependencies:

static <T> void process(List<T> list1, List<T> list2, List<T> insertList, List<T> deleteList) {
    for (T t: list1) {
        if (!list2.contains(t)) {
            insertList.add(t);
        }
    }
    for (T t: list2) {
        if (!list1.contains(t)) {
            deleteList.add(t);
        }
    }
}

Don't forget to override equals and hashcode methods for you class Officer in both cases. Please refer here for explanation

edited May 23, 2017 at 12:24

CommunityBot

11 silver badge

answered Jun 6, 2013 at 11:34

Tala

8,9685 gold badges36 silver badges38 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

jlordo · Accepted Answer · 2013-06-06 11:09:05Z

1

Make sure your Officer class overrides the equals() (and hashCode()) method and it will be really easy:

List<Officer> list1 = ... // your list1
List<Officer> list2 = ... // your list2
List<Officer> insertLst = new ArrayList<>(list1);
insertLst.removeAll(list2);
List<Officer> deleteList= new ArrayList<>(list2);
deleteList.removeAll(list1);

answered Jun 6, 2013 at 11:09

jlordo

37.9k7 gold badges63 silver badges84 bronze badges

5 Comments

fge Over a year ago

.equals() and hashCode()!

user2336315 Over a year ago

When you override equals, override hashCode too

jlordo Over a year ago

@fge: is hashCode() necessary for lists?

fge Over a year ago

@jlordo honestly, I don't know, but I'd never go about implementing .equals() only since you break the Object contract... And you'd have bad surprises if you decided on a Set ;)

jlordo Over a year ago

@fge: the object contract is a good point here. I don't think hashCode() is used in this particualr use case.

user1946562 · Accepted Answer · 2013-06-06 11:09:33Z

0

final List<Officer> one = new ArrayList<Officer>();
...
final List<Officer> two = new ArrayList<Officer>();
...
final List<Officer> insertList = new ArrayList<Officer>(one);
insertList.removeAll(two);
final List<Officer> removeList = new ArrayList<Officer>(two);
removeList.removeAll(one);

Edit: As jlordo said, make sure you override hashCode and Equals

answered Jun 6, 2013 at 11:09

user1946562

Comments

MaVRoSCy · Accepted Answer · 2013-06-06 11:12:19Z

0

You have to loop through the two lists ....

One way to do this could be this one:

ArrayList <Officer> list1= ....
ArrayList <Officer> list2= ....
ArrayList <Officer> insertList= new  ArrayList <Officer>();
ArrayList <Officer> deleteList= new  ArrayList <Officer>();

for(Officer x:list1){
  for(Officer y:list2){
     //business logic here
     if(x.id==y.id){
       insertList.add(x); //example code to add an Object in a List
     }
  }
}

The business logic part is up to you... you can compare data between the two lists and decide what goes where...

Hope this helps

answered Jun 6, 2013 at 11:12

MaVRoSCy

17.9k15 gold badges87 silver badges129 bronze badges

Collectives™ on Stack Overflow

How to compare two Arraylists which contain objects of the same class in Java?

4 Answers 4

Comments

5 Comments

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

4 Answers 4

Comments

5 Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related