List to Set in Java

11 Dec, 2018
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 program to demonstrate conversion of// list to set using simple traversalimport 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 program to demonstrate conversion of// list to set using constructorimport 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 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 program to demonstrate conversion of// Set to list using streamimport 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);    }}
Java-ArrayList
Java-Collections
java-hashset
java-LinkedList
java-list
Java-List-Programs
Java-Set-Programs
java-stream
Java-Stream-programs
java-treeset
Java
Java
Java-Collections
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