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Set to Array in Java

  • Difficulty Level : Easy

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 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 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 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()
        arr = s.toArray(arr);
  
        System.out.println(Arrays.toString(arr));
    }
}
Output:
[Geeks, for]

Method 4 (Using Arrays.copyOf())




// 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 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));
    }
}
Output:
[Geeks, for]

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