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List to Set in Java

Last Updated : 11 Dec, 2018
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Given a list (ArrayList or LinkedList), convert it into a set (HashSet or TreeSet) of strings in Java. Method 1 (Simple) We simply create an list. We traverse the given set and one by one add elements to the list. Java 
// Java program to demonstrate conversion of // list to set using simple traversal import java.util.*; class Test {  public static void main(String[] args)  {  // Creating a list of strings  List<String> aList = Arrays.asList("Geeks", "for",  "GeeksQuiz", "GeeksforGeeks", "GFG");  Set<String> hSet = new HashSet<String>();  for (String x : aList)  hSet.add(x);  System.out.println("Created HashSet is");  for (String x : hSet)  System.out.println(x);  // We can created TreeSet same way  } }
Method 2 (Using HashSet or TreeSet Constructor) Java 
// Java program to demonstrate conversion of // list to set using constructor import java.util.*; class Test {  public static void main(String[] args)  {  // Creating a list of strings  List<String> aList = Arrays.asList("Geeks", "for",  "GeeksQuiz", "GeeksforGeeks", "GFG");  // Creating a hash set using constructor  Set<String> hSet = new HashSet<String>(aList);  System.out.println("Created HashSet is");  for (String x : hSet)  System.out.println(x);  System.out.println("Created TreeSet is");  Set<String> tSet = new TreeSet<String>(aList);  System.out.println("Created TreeSet is");  for (String x : tSet)  System.out.println(x);  } }
Method 3 (Using addAll method) Java 
// Java program to demonstrate conversion of // Set to array using addAll() method. import java.util.*; class Test {  public static void main(String[] args)  {  // Creating a list of strings  List<String> aList = Arrays.asList("Geeks", "for",  "GeeksQuiz", "GeeksforGeeks", "GFG");  Set<String> hSet = new HashSet<String>(aList);  hSet.addAll(aList);  System.out.println("Created HashSet is");  for (String x : hSet)  System.out.println(x);  Set<String> tSet = new TreeSet<String>(aList);  tSet.addAll(aList);  System.out.println("Created TreeSet is");  for (String x : tSet)  System.out.println(x);  } }
Method 4 (Using stream in Java) We use stream in Java to convert given list to stream, then stream to set. This works only in Java 8 or versions after that. Java 
// Java program to demonstrate conversion of // Set to list using stream import java.util.*; import java.util.stream.*; class Test {  public static void main(String[] args)  {  // Creating a list of strings  List<String> aList = Arrays.asList("Geeks", "for",  "GeeksQuiz", "GeeksforGeeks", "GFG");  // Converting to set using stream  Set<String> set = aList.stream().collect(Collectors.toSet());  for (String x : set)  System.out.println(x);  } }

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