HashSet extends AbstractSet and implements the Set interface. It creates a collection that uses a hash table for storage. It stores information by using a mechanism called hashing. In hashing, the informational content of a key is used to determine a unique value, called its hash code.
There are three simple ways to iterate over a HashSet, which is the following :
- Using Iterator
- Without using Iterator (using for loop)
- Using for-each loop
Method 1: Iterator method
In this method, we iterate HashSet with the help of iterator. First, we make an iterator to iterate HashSet with the help of the iterator() method in Java.
// Create a iterator of integer type to iterate HashSet Iterator<Integer> it = set.iterator();
And then iterate HashSet with the help of hasNext() and Next() method in Java. Where hasNext() method check whether HashSet has elements or not and, Next() method access the data of HashSet.
Note: Use Next() method only one time after hasNext().
Example:
Java
// Java program to iterate the HashSet// using iterator import java.util.*; class GFG { public static void main(String[] args) { // Creating a new HashSet for iteration HashSet<Integer> set = new HashSet<>(); // Add data to HashMap set.add(10); set.add(20); // Duplicates not allowed in HashMap, so avoid by // HashMap set.add(10); set.add(50); // Duplicates not allowed in HashMap, so avoid by // HashMap set.add(50); // Create a iterator of type integer to iterate // HashSet Iterator<Integer> it = set.iterator(); System.out.println( "Iterate HashSet using iterator : "); // Iterate HashSet with the help of hasNext() and // next() method while (it.hasNext()) { // Print HashSet values System.out.print(it.next() + " "); } }} |
Iterate HashSet using iterator : 50 20 10
Method 2: Iterate using for loop
In this method, we iterate HashSet using a simple for loop. Below is the implementation of this approach:
Example:
Java
// Java program to iterate the HashSet// using for loop import java.util.*; class GFG { public static void main(String[] args) { // Creating a new HashSet for iteration HashSet<String> set = new HashSet<>(); // Add data to HashSet set.add("Hello"); set.add("geeks"); set.add("on"); // duplicates not allowed in HashMap, so avoid by // HashMap set.add("geeks"); set.add("for"); // duplicates not allowed in HashMap, so avoid by // HashMap set.add("geeks"); System.out.println( "Iterate HashSet using for loop : "); // Iterate throw a simple for loop for (String ele : set) { // Print HashSet data System.out.print(ele + " "); } }} |
Iterate HashSet using for loop : Hello geeks for on
Method 3: Using forEach() method
In this method, we iterate HashSet using forEach() loop in Java. Below is the implementation of this method:
Example:
Java
// Java program to iterate using forEach() loop import java.util.*; class GFG { public static void main(String[] args) { // Creating a new HashSet for iteration HashSet<String> set = new HashSet<>(); // Add data to HashSet set.add("Hello"); set.add("geeks"); set.add("on"); // duplicates not allowed in HashMap, so avoid by // HashMap set.add("geeks"); set.add("for"); // duplicates not allowed in HashMap, so avoid by // HashMap set.add("geeks"); System.out.println( "Iterate HashSet using forEach loop : "); // Iterate throw a forEach method in Java set.forEach(System.out::println); }} |
Iterate HashSet using forEach loop : Hello geeks for on