How to Convert Set to List (HashSet to ArrayList)
This tutorial shows you how to convert Set to List in Java using different ways.
Convert Set to List Example
package com.sneppets.example;
import java.util.ArrayList;
import java.util.HashSet;
import java.util.List;
import java.util.Set;
import java.util.stream.Collectors;
public class ConvertSetToListExample {
public static void main(String[] args) {
System.out.println("Set elements..");
Set<String> hashSet = new HashSet<>();
hashSet.add("a");
hashSet.add("b");
hashSet.add("c");
hashSet.add("d");
for(String str : hashSet) {
System.out.println(str);
}
System.out.println("Convert Set to List....");
System.out.println("Method 1: ArrayList Constructor");
//Using ArrayList constructor
List<String> list = new ArrayList<>(hashSet);
printList(list);
System.out.println("Method 2: Java 8 Stream");
//Using Java 8
List<String> listJava8 = hashSet.stream().collect(Collectors.toList());
printList(listJava8);
}
private static void printList(List<String> list) {
for(String str : list) {
System.out.println(str);
}
}
}
Ouput
Set elements.. a b c d Convert Set to List.... Method 1: ArrayList Constructor a b c d Method 2: Java 8 Stream a b c d
1. Constructor
You can make use to ArrayList constructor ArrayList(Collection<? extends E> c) which can be used to construct list containing the elements of specified collection as an argument.
List<String> list = new ArrayList<>(hashSet);
2. Java 8 Stream
Using Java 8, you can make use of Stream API to convert a Set to List by performing collect operation on the stream and then use Collectors.toList() to accumulate elements into a List as shown.
List<String> listJava8 = hashSet.stream().collect(Collectors.toList());
3. Other Libraries
There are other libraries and utils available to perform this conversion like Guava and oracle.javatools.util.ImmutableList<E>
3.1 Guava’s Lists.newArrayList()
//Method to convert set to list
public List<String> convertToList(Set<String> set)
{
return Lists.newArrayList(set);
}
3.2 ImmutableList.copyOf()
//Method to convert set to list
public List<String> convertToList(Set<String> set)
{
return ImmutableList.copyOf(set);
}
Also See
- How to manipulate Java 8 Stream data sources or objects?
- Replace element in ArrayList at specific index
- Convert Integer List to int array
- Round up a Float value to an Int value