How do you turn an ArrayList into a Set in Java?

An ArrayList can be converted to a set object using Set constructor. The resultant set will elliminate any duplicate entry present in the list and will contains only the unique values.

Set<String> set = new HashSet<>(list);

Or we can use set.addAll() method to add all the elements of the list to the set.

set.addAll(list);

Using streams as well, we can get a set from a list.

set = list.stream().collect(Collectors.toSet());

Example

Following is the example showing the list to set conversion via multiple ways −

package com.tutorialspoint;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.HashSet;
import java.util.List;
import java.util.Set;
import java.util.stream.Collectors;

public class CollectionsDemo {
   public static void main(String[] args) {
      List<Integer> list = new ArrayList<>(Arrays.asList(1, 2, 3, 4, 4, 5, 5));
      System.out.println("ArrayList: " + list);
      Set<Integer> set = new HashSet<>(list);
      System.out.println("Set: " + set);
      set = new HashSet<>();
      set.addAll(list);
      System.out.println("Set: " + set);
      set = new HashSet<>();
      set = list.stream().collect(Collectors.toSet());
      System.out.println("Set: " + set);
   }
}

Output

This will produce the following result −

ArrayList: [1, 2, 3, 4, 4, 5, 5]
Set: [1, 2, 3, 4, 5]
Set: [1, 2, 3, 4, 5]
Set: [1, 2, 3, 4, 5]