Two Arraylists have the same elements but in different order, are they equal?

Question

I have two arraylist's, both have 3 elements each. PL1 and INITIAL1 are to array list's. INITIAL1 will be initialized with values, PL1 will be edited dynamically. If both are equal, then an operation will be performed else nothing.

PL1 = [00, 01, 02]
INITIAL1 = [01, 02, 00]

Values are same but in different order. are these two equal?

will I be able to conclude that both are equivalent and perform some operation?

Two array list in java are said to be equal when the contain the same number of element, with same content and in same order. To check it you can use **.equals()** function. — Ayush Mishra, Jun 09 '19 at 06:59
Yeah okay. Check out the link in my previous comment - your question is an exact *dup* of that question. — Nicholas K, Jun 09 '19 at 07:05

Shashank Dwivedi · Answer 1 · 2019-06-09T07:18:18.687

1

Two Lists are considered equal if elements in each List are exactly the same by equals method including their order in Lists. So to answer your questions,

Values are same but in different order. are these two equal?

Since they are in a different order, they are not equal.

will I be able to conclude that both are equivalent and perform some operation?

I don't know why you need to do this but it is possible. You can use HashMap to store INITIALS as key and check if size of PL1 is same as Map's size and Map contains all values in PL1 by equals check.

Or Simply use Apache Commons CollectionUtils.isEqualCollection(Collection a, Collection b)

edited Jun 09 '19 at 07:18

answered Jun 09 '19 at 07:09

Shashank Dwivedi

357
3
8

you can do it without the use of HashMap too. – Ayush Mishra Jun 09 '19 at 07:19
HashSet or HashMap can be used for reducing iteration to least. Otherwise best would be to use the existing Apache library. – Shashank Dwivedi Jun 09 '19 at 07:22

score 0 · Accepted Answer · answered Jun 09 '19 at 07:04

0

if (INITIAL1.size() == PL1.size() && INITIAL1.containsAll(PL1)) {
  //do something
}

answered Jun 09 '19 at 07:04

ivarkol

39
3

Will this work without sorting? – Deep Chhowala Jun 09 '19 at 07:07
1

This is not ideal solution. Consider the following input list1 = [1, 2, 3, 4, 3] & list2 = [1, 2, 3, 4, 4] According to your logic, the answer is true for the above input – IamVickyAV Jun 09 '19 at 07:13
@DeepChhowala, yes without sorting also you can do, check out my answer. I exaplined with code and a link , that might help you. – Ayush Mishra Jun 09 '19 at 07:14
yes, without. Each element of INITIAL1 will be compared with each element of PL1. – ivarkol Jun 09 '19 at 07:15
@ivarkol working. Done Man. Thankyou – Deep Chhowala Jun 09 '19 at 07:53
1

How @IamVickyAV noticed, this solution don't work for lists which have non-unique elements. If your lists have only unique elements use Set instead of List. – ivarkol Jun 09 '19 at 08:14

score 0 · Answer 3 · answered Jun 09 '19 at 07:09

Two array list in java are said to be equal when the contain the same number of element, with same content and in same order. To check it you can use .equals() function

for example:

import java.util.*;
public class HelloWorld{

     public static void main(String []args){
      ArrayList<String> list1=new ArrayList<String>();//Creating arraylist 
      list1.add("Ravi");//Adding object in arraylist    
      list1.add("Vijay");    
      list1.add("Ravi");    
      list1.add("Ajay");    
      //Invoking arraylist object   
      System.out.println(list1); 

      ArrayList<String> list2=new ArrayList<String>();//Creating arraylist 
      list2.add("Ravi");//Adding object in arraylist    
      list2.add("Vijay");    
      list2.add("Ravi");    
      list2.add("Ajay");    
      //Invoking arraylist object   
      System.out.println(list2); 

      if(list1.equals(list2)) {
          System.out.println("yes");
      }
     }
}

your Array list won't evaluate to equal since they have different element in different order.

and if you want that they evaluate to true without sorting then checkout this link

Java ArrayList - how can I tell if two lists are equal, order not mattering?

score 0 · Answer 4 · edited Jun 09 '19 at 08:17

package com.practice;    
import java.util.ArrayList;
import java.util.List;
public class twoArray 
{
    public static void main(String[] args) 
    {
        List<Integer> list1 = new ArrayList<>();
        List<Integer> list2 = new ArrayList<>();

        list1.add(00);
        list1.add(01);
        list1.add(02);
        System.out.println(list1 +" Array list 1");   // [00,01,02] Array list 1

        list2.add(01);
        list2.add(02);
        list2.add(00);
        System.out.println(list2 +" Array list 2");   // [01,02,00] Array list 2

        System.out.println(list1.equals(list2));       // output: **false**         
    }
}

I hope after going through this example you got an idea. As the ArrayList internally uses the index (position) to store the values. As per your requirements [00,01,02] and [01,02,00] the values are same and the ordering is different and hence your using ArrayList it returns false! And it's not equal and and you won't be able to perform any operations.

The best solution for this is you just sort both PL1 and INITIAL1 and it returns true.

Two Arraylists have the same elements but in different order, are they equal?

4 Answers4