5 Best Ways to Iterate a Java HashMap: Code Examples & Tips

1. Iterate HashMap using EntrySet with Iterator

Use an Iterator on the entrySet() to access both keys and values.

Map<Integer, String> coursesMap = new HashMap<>();
coursesMap.put(1, "C");
coursesMap.put(2, "C++");
coursesMap.put(3, "Java");
coursesMap.put(4, "Spring Framework");
coursesMap.put(5, "Hibernate ORM framework");

Iterator<Map.Entry<Integer, String>> iterator = coursesMap.entrySet().iterator();
while (iterator.hasNext()) {
    Map.Entry<Integer, String> entry = iterator.next();
    System.out.println(entry.getKey());
    System.out.println(entry.getValue());
}

2. Iterate HashMap using KeySet with Iterator

Iterate over the keys and retrieve values via get().

Map<Integer, String> coursesMap = new HashMap<>();
// (populate map as above)

Iterator<Integer> iterator = coursesMap.keySet().iterator();
while (iterator.hasNext()) {
    Integer key = iterator.next();
    System.out.println(key);
    System.out.println(coursesMap.get(key));
}

3. Iterate HashMap with Enhanced For‑Each Loop

The enhanced for loop simplifies iteration over entrySet().

for (Map.Entry<Integer, String> entry : coursesMap.entrySet()) {
    System.out.println(entry.getKey());
    System.out.println(entry.getValue());
}

4. Iterate HashMap using Lambda Expression

Leverage Map.forEach with a lambda to process each key‑value pair.

coursesMap.forEach((key, value) -> {
    System.out.println(key);
    System.out.println(value);
});

5. Iterate HashMap with Stream API

Use streams to traverse entries in a functional style.

coursesMap.entrySet().stream().forEach(entry -> {
    System.out.println(entry.getKey());
    System.out.println(entry.getValue());
});

Each method prints the key followed by its corresponding value, illustrating the most common patterns for HashMap traversal in Java.