Set to Array in Java

Last Updated : 29 Mar, 2024

Given a set (HashSet or TreeSet) of strings in Java, convert it into an array of strings.

Input : Set hash_Set = new HashSet();
        hash_Set.add("Geeks");
        hash_Set.add("For");
Output : String arr[] = {"Geeks", "for"}

Method 1 (Simple) We simply create an empty array. We traverse the given set and one by one add elements to the array.

Java

// Java program to demonstrate conversion of 
// Set to array using simple traversal
import java.util.*;

class Test {
    public static void main(String[] args)
    {
        // Creating a hash set of strings
        Set<String> s = new HashSet<String>();
        s.add("Geeks");
        s.add("for");

        int n = s.size();
        String arr[] = new String[n];

        int i = 0;
        for (String x : s)
            arr[i++] = x;

        System.out.println(Arrays.toString(arr));
    }
}

Output:

[Geeks, for]

Method 2 (Using System.arraycopy())

Java

// Java program to demonstrate conversion of 
// Set to array using simple traversal
import java.util.*;

class Test {
    public static void main(String[] args)
    {
        // Creating a hash set of strings
        Set<String> s = new HashSet<String>();
        s.add("Geeks");
        s.add("for");

        int n = s.size();
        String arr[] = new String[n];

        // Copying contents of s to arr[]
        System.arraycopy(s.toArray(), 0, arr, 0, n);

        System.out.println(Arrays.toString(arr));
    }
}

Output:

[Geeks, for]

Method 3 (Using toArray())

Java

// Java program to demonstrate conversion of 
// Set to array using toArray()
import java.util.*;

class Test {
    public static void main(String[] args)
    {
        // Creating a hash set of strings
        Set<String> s = new HashSet<String>();
        s.add("Geeks");
        s.add("for");

        int n = s.size();
        String arr[] = new String[n];

        // Please refer below post for syntax
        // details of toArray()
        // https://www.geeksforgeeks.org/java/arraylist-array-conversion-java-toarray-methods/
        arr = s.toArray(arr);

        System.out.println(Arrays.toString(arr));
    }
}

Output:

[Geeks, for]

Method 4 (Using Arrays.copyOf())

Java

// Java program to demonstrate conversion of 
// Set to array using Arrays.copyOf()
import java.util.*;

class Test {
    public static void main(String[] args)
    {
        // Creating a hash set of strings
        Set<String> s = new HashSet<String>();
        s.add("Geeks");
        s.add("for");

        String[] arr = 
          Arrays.copyOf(s.toArray(), s.size(), String[].class);

        System.out.println(Arrays.toString(arr));
    }
}

Output:

[Geeks, for]

Method 5 (Using stream in Java) We use stream in Java to convert given set to steam, then stream to array. This works only in Java 8 or versions after that.

Java

// Java program to demonstrate conversion of 
// Set to array using stream
import java.util.*;

class Test {
    public static void main(String[] args)
    {
        // Creating a hash set of strings
        Set<String> s = new HashSet<String>();
        s.add("Geeks");
        s.add("for");

        int n = s.size();
        String[] arr = s.stream().toArray(String[] ::new);

        System.out.println(Arrays.toString(arr));
    }
}