Last Updated : 11 Jul, 2025
Java Set is a part of java.util package and extends java.util.Collection interface. It does not allow the use of duplicate elements and at max can accommodate only one null element. Few important features of the Java Set interface are as follows:
In this post different methods to convert a List interface to Set in Java are discussed:
Way 1: Naive Approach: The naive solution is to create an empty set and add every element of the specified list to the newly created set. Below is the implementation of the naive approach:
Java
// Java Program to convert
// List to Set in Java 8
import java.util.*;
import java.util.stream.*;
import java.util.function.Function;
class GFG {
// Generic function to convert list to set
public static <T> Set<T> convertListToSet(List<T> list)
{
// create an empty set
Set<T> set = new HashSet<>();
// Add each element of list into the set
for (T t : list)
set.add(t);
// return the set
return set;
}
public static void main(String args[])
{
// Create a stream of integers
List<String> list = Arrays.asList("GeeksForGeeks",
"Geeks",
"forGeeks",
"A computer portal",
"for",
"Geeks");
// Print the List
System.out.println("List: " + list);
// Convert List to stream
Set<String> set = convertListToSet(list);
// Print the Set
System.out.println("Set from List: " + set);
}
}
Output:
List: [GeeksForGeeks, Geeks, forGeeks, A computer portal, for, Geeks] Set from List: [Geeks, for, GeeksForGeeks, A computer portal, forGeeks]
Way 2: Using Constructor: HashSet constructor can take another collection object to construct a new set containing the elements of the specified list. Below is the implementation of the above approach:
Java
// Java Program to convert
// List to Set in Java 8
import java.util.*;
import java.util.stream.*;
class GFG {
// Generic function to convert list to set
public static& lt;
T& gt;
Set& lt;
T& gt;
convertListToSet(List& lt; T & gt; list)
{
// create a set from the List
return new HashSet& lt;
>
(list);
}
public static void main(String args[])
{
// Create a stream of integers
List& lt;
String& gt; list = Arrays.asList("GeeksForGeeks",
"Geeks",
"forGeeks",
"A computer portal",
"for",
"Geeks");
// Print the List
System.out.println(" List : " + list);
// Convert List to stream
Set& lt;
String& gt;
set = convertListToSet(list);
// Print the Set
System.out.println(" Set from List
: "
+ set);
}
}
Output:
List: [GeeksForGeeks, Geeks, forGeeks, A computer portal, for, Geeks] Set from List: [Geeks, for, GeeksForGeeks, A computer portal, forGeeks]
Way 3: Using Java 8 Stream API: HashSet constructor can take another collection object to construct a new set containing the elements of the specified list. Below is the implementation of the above approach:
Java
// Java Program to convert
// List to Set in Java 8
import java.util.*;
import java.util.stream.*;
class GFG {
// Generic function to convert list to set
public static <T> Set<T> convertListToSet(List<T> list)
{
// create a set from the List
return list.stream().collect(Collectors.toSet());
}
public static void main(String args[])
{
// Create a stream of integers
List<String> list = Arrays.asList("GeeksForGeeks",
"Geeks",
"forGeeks",
"A computer portal",
"for",
"Geeks");
// Print the List
System.out.println("List: " + list);
// Convert List to stream
Set<String> set = convertListToSet(list);
// Print the Set
System.out.println("Set from List: " + set);
}
}
Output:
List: [GeeksForGeeks, Geeks, forGeeks, A computer portal, for, Geeks] Set from List: [Geeks, for, GeeksForGeeks, A computer portal, forGeeks]
Way 4: Using Guava Sets.newHashSet(): Sets.newHashSet() creates a mutable HashSet instance containing the elements of the specified list. Below is the implementation of the above approach:
Java
// Java Program to convert
// List to Set in Java 8
import java.util.*;
import java.util.stream.*;
class GFG {
// Generic function to convert list to set
public static <T> Set<T> convertListToSet(List<T> list)
{
// create a set from the List
return return Sets.newHashSet(list);
}
public static void main(String args[])
{
// Create a stream of integers
List<String> list = Arrays.asList("GeeksForGeeks",
"Geeks",
"forGeeks",
"A computer portal",
"for",
"Geeks");
// Print the List
System.out.println("List: " + list);
// Convert List to stream
Set<String> set = convertListToSet(list);
// Print the Set
System.out.println("Set from List: " + set);
}
}
Output:
List: [GeeksForGeeks, Geeks, forGeeks, A computer portal, for, Geeks] Set from List: [Geeks, for, GeeksForGeeks, A computer portal, forGeeks]
Way 5: Using addAll() method in Collection package
In this, we can convert the list items to set by using addAll() method. For this, we have to import the package java.util.Collection.
This addAll(Collection c) method is a boolean datatype. It is used to add the collection of one object to the collection of another object
Java
import java.util.*;
import java.util.stream.*;
class GFG {
// Generic function to convert list to set
public static <T> Set<T> convertListToSet(List<T> list)
{
// create a set from the List using addAll() method
HashSet<T> set = new HashSet<>();
set.addAll(list);
return set;
}
public static void main(String args[])
{
// Create a stream of integers
List<String> list = Arrays.asList(
"GeeksForGeeks", "Geeks", "forGeeks",
"A computer portal", "for", "Geeks");
// Print the List
System.out.println("List: " + list);
// Convert List to stream
Set<String> set = convertListToSet(list);
// Print the Set
System.out.println("Set from List: " + set);
}
}
Output:
List: [GeeksForGeeks, Geeks, forGeeks, A computer portal, for, Geeks] Set from List: [Geeks, for, GeeksForGeeks, A computer portal, forGeeks]
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