util package and is one of the most commonly used data structures for storing key-value pairs. Iterating over a HashMap efficiently is essential for performing operations like searching, updating, or processing data stored in the map. In this article, we will explore different ways to iterate over hashmap java.

Different Ways to Iterate Over a HashMap

1. Using entrySet() and a For-Each Loop

This is the most common and recommended approach. The entrySet() method returns a set view of the mappings contained in the map.
import java.util.HashMap;
import java.util.Map;

public class HashMapIteration {
public static void main(String[] args) {
HashMap<Integer, String> map = new HashMap<>();
map.put(1, "Apple");
map.put(2, "Banana");
map.put(3, "Cherry");

for (Map.Entry<Integer, String> entry : map.entrySet()) {
System.out.println("Key: " + entry.getKey() + ", Value: " + entry.getValue());
}
}
}
2. Using keySet() to Iterate Over Keys

If you only need the keys, you can use keySet() to retrieve a set of keys and loop through them.
for (Integer key : map.keySet()) {
System.out.println("Key: " + key + ", Value: " + map.get(key));
}
This approach requires an additional lookup (map.get(key)) to retrieve values, making it less efficient than entrySet().

3. Using values() to Iterate Over Values

If you only need to iterate over values without keys, you can use values().
for (String value : map.values()) {
System.out.println("Value: " + value);
}
4. Using Java 8 Streams

With Java 8, you can use streams to iterate over a HashMap in a more functional style.
map.forEach((key, value) -> System.out.println("Key: " + key + ", Value: " + value));
Alternatively, using streams:
map.entrySet().stream().forEach(entry ->
System.out.println("Key: " + entry.getKey() + ", Value: " + entry.getValue()));
5. Using an Iterator

You can use an Iterator to iterate over a HashMap, especially when you need to remove elements while iterating.
Iterator<Map.Entry<Integer, String>> iterator = map.entrySet().iterator();
while (iterator.hasNext()) {
Map.Entry<Integer, String> entry = iterator.next();
System.out.println("Key: " + entry.getKey() + ", Value: " + entry.getValue());
}
Conclusion

Java provides multiple ways to iterate over a HashMap, each with its own advantages. The entrySet() method is the most efficient for iterating over both keys and values, while Java 8 streams offer a modern, concise approach. Using an iterator is useful when modifications are needed during iteration. Choosing the right method depends on your specific use case and performance considerations