Difference between ArrayList and HashSet in Java

HashSet and ArrayList both are some of the most important classes of the Java Collection framework.

The following are the important differences between ArrayList and HashSet.

Sr. No.	Key	ArrayList	HashSet
1	Implementation	ArrayList is the implementation of the list interface.	HashSet on the other hand is the implementation of a set interface.
2	Internal implementation	ArrayList internally implements array for its implementation.	HashSet internally uses Hashmap for its implementation.
3	Order of elements	ArrayList maintains the insertion order i.e order of the object in which they are inserted.	HashSet is an unordered collection and doesn't maintain any order.
4	Duplicates	ArrayList allows duplicate values in its collection.	On other hand duplicate elements are not allowed in Hashset.
5	Index performance	ArrayList uses index for its performance i.e its index based one can retrieve object by calling get(index) or remove objects by calling remove(index)	HashSet is completely based on object also it doesn't provide get() method.
6	Null Allowed	Any number of null value can be inserted in arraylist without any restriction.	On other hand Hashset allows only one null value in its collection,after which no null value is allowed to be added.

Example of ArrayList vs Hashset

JavaTester.java

import java.io.*;
import java.util.*;
public class JavaTester {
   public static void main(String[] args) throws IOException{
      int n = 5;
      List<Integer> al = new ArrayList<>(n);
      for (int i = 1; i <= n; i++) {
         al.add(i);
      }
      System.out.println(al);
      al.remove(3);
      System.out.println(al);
      for (int i = 0; i < al.size(); i++) {
         System.out.print(al.get(i) + " ");
      }
   }
}

Output

[1, 2, 3, 4, 5]
[1, 2, 3, 5]
1 2 3 5

Example

JavaTester.java

import java.util.HashSet;
import java.util.Set;
public class JavaTester {
   public static void main(String[] args){
      Set<Integer> hs = new HashSet<>();
      hs.add(1);
      hs.add(2);
      hs.add(3);
      hs.add(4);
      hs.add(4);
      for (Integer temp : hs) {
         System.out.print(temp + " ");
      }
   }
}

Output

1 2 3 4