You can iterate a HashSet by using either forEach(Consumer), since Java 8, or for-each loop, Iterator, and SplitIterator
The iteration order is unpredictable as HashSet has no guarantee to it
Index-loops such as for-index, while-index, do-while-index cannot be used to iterate a HashSet as it has no support on retrieving element by index
Let's walk through the below examples to explore them in more details
Iterate with Java 8+ forEach(Consumer)
Use forEach(Consumer), since Java 8, to iterate over a HashSet
NullPointerException will be thrown if the specified consumer action or the caller HashSet is null
@Test
public void iterateWithForEachConsumer() {
Set<Integer> set = new HashSet<>(Set.of(3, 1, 2));
set.forEach(ele -> System.out.printf("%d ", ele));
}
Iterate with a for-each loop
- Use a for-each loop to iterate over a HashSet
@Test
public void iterateWithForEach() {
Set<Integer> set = new HashSet<>(Set.of(3, 1, 2));
for (int ele : set) {
System.out.printf("%d ", ele);
}
}
Iterate with Iterator and SplitIterator
Use Iterator and SplitIterator to iterate over a collection in normal and parallel respectively
You can remove an element when iterating with an iterator while other methods can't
@Test
public void iterateWithIterator() {
Set<Integer> set = new HashSet<>(Set.of(3, 1, 2));
Iterator<Integer> iterator = set.iterator();
while (iterator.hasNext()) {
System.out.printf("%d ", iterator.next());
}
}
Conclusion
In this tutorial, we learned some ways to iterate over a HashSet by using Java 8+ forEach(Consumer), for-each loop and iterator. You can find the full source code as below