Comparing two ArrayLists and remove duplicates from original ArrayList

Question

I have two Custom Arraylist:

List<Item> before = new ArrayList<Item>();
List<ItemEx> after = new ArrayList<ItemEx>();

before.add(new Item(1L,"test1"));
before.add(new Item(2L,"test2"));
before.add(new Item(3L,"test3"));

after.add(new ItemEx(1L,"test4"));
after.add(new ItemEx(2L,"test5"));
after.add(new ItemEx(4L,"test6")); 
after.add(new ItemEx(5L,"test7"));

I want to store the elements in the List<ItemEx> after and the element shoulds be after the removing of common element is {3L, 4L, 5L}.

add items from both list into HASHSET, after that you get only, 1L,2L,3L,4L,5Lin hashset — Divyesh Patel
– Divyesh Patel, Commented May 29, 2017 at 8:22
after.removeAll(before) works if you can somehow compare the objects correctly (maybe override .equals method). @DivyeshPatel how does this remove common elements from after list? — XtremeBaumer
– XtremeBaumer, Commented May 29, 2017 at 8:24
HASHSET allows only unique entry, so it store only unique data — Divyesh Patel
– Divyesh Patel, Commented May 29, 2017 at 8:26

IntelliJ Amiya · Accepted Answer · 2017-05-29 09:04:56Z

2

FYI

List<Item> & List<ItemEx> should be SAME TYPE .

Logic

List<String> before = new ArrayList<String>();
List<String> after = new ArrayList<String>(); 
List<String> list_checking = new ArrayList<String>(before);
                            list_checking.addAll(after);
                            List<String> list_common = new ArrayList<String>(before);
                            list_common.retainAll(after);
                            list_checking.removeAll(list_common);

edited May 29, 2017 at 9:04

answered May 29, 2017 at 8:51

IntelliJ Amiya

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1 Comment

Shikha Ratra Over a year ago

my ArrayList is not of same type

Divyesh Patel · Accepted Answer · 2017-05-29 08:28:53Z

0

Try this :

HashSet hs = new HashSet();
hs.addAll(before);
hs.addAll(after);
after.clear();
after.addAll(hs);

Now, in after list you get desire values.

answered May 29, 2017 at 8:28

Divyesh Patel

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Comments

R.Shanmukha sai · Accepted Answer · 2017-05-29 08:57:00Z

0

Its simple. Take a copy of the existing one into a temporary Variable if you want for future use.

ArrayList temporiginalArrList=OriginalArrayList; //here 'T' can be a specific object to want to save

OriginalArrayList.removeAll(secondArrayList);

answered May 29, 2017 at 8:57

R.Shanmukha sai

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