Convert HashSet to array in Java

Java HashSet class is used to create a collection that uses a hash table for the storage of elements. It inherits AbstractSet class and implements Set Interface. 

The key points about HashSet are:

• HashSet contains unique elements only.
• HashSet allows null values.
• The insertion of elements in a HashSet is based on a hashcode.
• HashSet is best used for searching problems.

There are two ways of converting HashSet to the array:

1. Traverse through the HashSet and add every element to the array.
2. To convert a HashSet into an array in java, we can use the function of toArray().

Method 1: By traversing the set add elements to the array

We can traverse the Set using a simple for loop and then add elements one by one to the array.

Java

// Java program to convert HashSet to array

import java.io.*;
import java.util.*;

class GFG {
    public static void main(String[] args)
    {
        HashSet<String> set = new HashSet<String>();
        set.add("1");
        set.add("13");
        set.add("27");
        set.add("87");
        set.add("19");

        System.out.println("Hash Set Contains :" + set);
        String arr[] = new String[set.size()];

        int i=0;

        // iterating over the hashset
        for(String ele:set){
          arr[i++] = ele;
        }

        for (String n : arr)
            System.out.println(n);
    }
}

Output

Hash Set Contains :[1, 13, 27, 19, 87]
1
13
27
19
87

Method 2: Using toArray() method

Syntax:

public Object[] toArray()
           or
public <T> T[] toArray(T[] a)

Parameters: This method either accepts no parameters or it takes an array T[] a as a parameter which is the array into which the elements of the list are to be stored if it is big enough; otherwise, a new array of the same runtime type is allocated for this purpose.

Return Value: The function returns an array containing all the elements in this list.

Java

// Java program to convert HashSet to array

import java.io.*;
import java.util.*;

class GFG {
    public static void main(String[] args)
    {
        HashSet<String> set = new HashSet<String>();
        set.add("1");
        set.add("13");
        set.add("27");
        set.add("87");
        set.add("19");

        System.out.println("Hash Set Contains :" + set);
        String arr[] = new String[set.size()];

        // toArray() method converts the set to array
        set.toArray(arr);

        for (String n : arr)
            System.out.println(n);
    }
}

Output

Hash Set Contains :[1, 13, 27, 19, 87]
1
13
27
19
87