How to Iterate Through Set in Java

1. Iterate Over Set/HashSet in Java Using Enhanced for Loop
2. Iterate a Vector Using Enumeration in Java
3. Iterate Over Set/HashSet in Java by Converting It Into an Array
4. Iterate Over Set/HashSet in Java by Using the stream() Method of the Array Class

This article will introduce how to iterate through Set or HashSet in Java without using the Iterator. An iterator is used to return the elements in random order. This task can be accomplished using various methods other than an iterator.

Iterate Over Set/HashSet in Java Using Enhanced for Loop

for-each loop in Java is also called an enhanced for loop. It is used to iterate through elements of arrays and collections in Java.

Here we have created a Set named mySet using the HashSet class, a collection of string elements. By calling the add() method on mySet we have added elements to mySet.

Using the enhanced for loop, we can iterate over each element inside the collection and print it out, as shown in the code. For each element s of type String in mySet, we can iterate over it. Note that elements iterate in an unordered collection.

import java.util.HashSet;
import java.util.Set;

public class IterateOverHashSet {
  public static void main(String[] args) {
    Set<String> mySet = new HashSet<>();
    mySet.add("Apple");
    mySet.add("Banana");
    mySet.add("Mango");

    for (String s : mySet) {
      System.out.println("s is : " + s);
    }
  }
}

Output:

s is : Mango
s is : Apple
s is : Banana

Iterate a Vector Using Enumeration in Java

Vector implements the List interface, which helps us create resizeable arrays similar to the ArrayList class. Firstly, we created a Set of string type elements using the HashSet class, later added elements to it using the add() method.

myset is then passed to the constructor of the Vector class, and then the elements() method is called on it to enumerate through the elements of Vector.

We then use a while loop to print till the Enumeration (e) has more elements. Consecutive calls to the method nextElements() return successive elements of the series.

import java.util.Enumeration;
import java.util.HashSet;
import java.util.Set;
import java.util.Vector;

public class IterateOverHashSet {
  public static void main(String[] args) {
    Set<String> mySet = new HashSet<>();
    mySet.add("Apple");
    mySet.add("Banana");
    mySet.add("Mango");

    Enumeration e = new Vector(mySet).elements();
    while (e.hasMoreElements()) {
      System.out.println(e.nextElement());
    }
  }
}

Output:

Mango
Apple
Banana

Iterate Over Set/HashSet in Java by Converting It Into an Array

We first create a Set of the String type elements and add items to mySet. To iterate over the elements, we convert our mySet to an array using the toArray() method. The toArray() method returns an array that has the same elements as in HashSet.

Then by using a for loop, we can loop over all the elements in the new array named myArray. Print each element, as shown in the code below.

import java.util.HashSet;
import java.util.Set;

public class IterateOverHashSet {
  public static void main(String[] args) {
    Set<String> mySet = new HashSet<>();
    mySet.add("Apple");
    mySet.add("Banana");
    mySet.add("Mango");

    String[] myArray = mySet.toArray(new String[mySet.size()]);
    for (int index = 0; index < myArray.length; index++) {
      System.out.println("element : " + myArray[index]);
    }
  }
}

Output:

element : Mango
element : Apple
element : Banana

Iterate Over Set/HashSet in Java by Using the stream() Method of the Array Class

In the code shown below, we first create a Set of String type elements using the HashSet class in Java. Then we add items to it by calling the add() method on its instance fruits.

The stream() method returns a sequential stream of collection. We convert our Set of String - fruits, into a stream. Later we displayed the elements of the stream using a lambda expression.

import java.util.HashSet;
import java.util.Set;
import java.util.stream.Stream;

public class Simple {
  public static void main(String args[]) {
    Set<String> fruits = new HashSet<>();
    fruits.add("Apple");
    fruits.add("Banana");
    fruits.add("Mango");

    Stream<String> stream = fruits.stream();
    stream.forEach((fruit) -> System.out.println(fruit));
  }
}

Output:

Apple
Mango
Banana