In Java, the HashMap class is a widely used data structure that allows you to store key-value pairs. Sometimes, you may need to iterate over the elements of a HashMap to perform certain operations. In this article, we will explore different ways to iterate over a HashMap in Java.

Method 1: Using EntrySet

The entrySet() method in the HashMap class returns a set view of the key-value pairs contained in the map. We can use this set to iterate over the elements of the HashMap.

HashMap<Integer, String> map = new HashMap<>();
map.put(1, "Apple");
map.put(2, "Banana");
map.put(3, "Orange");

for (Map.Entry<Integer, String> entry : map.entrySet()) {
    int key = entry.getKey();
    String value = entry.getValue();
    System.out.println("Key: " + key + ", Value: " + value);
}

In the above code, we use a for-each loop to iterate over the entrySet() of the HashMap. We retrieve the key-value pair from each entry using the getKey() and getValue() methods, and then print them.

Method 2: Using KeySet

The keySet() method in the HashMap class returns a set view of the keys contained in the map. We can use this set to iterate over the keys and retrieve their corresponding values from the HashMap.

HashMap<Integer, String> map = new HashMap<>();
map.put(1, "Apple");
map.put(2, "Banana");
map.put(3, "Orange");

for (Integer key : map.keySet()) {
    String value = map.get(key);
    System.out.println("Key: " + key + ", Value: " + value);
}

Here, we use a for-each loop to iterate over the keySet() of the HashMap. For each key, we use the get() method to retrieve the corresponding value from the HashMap.

Conclusion

Iterating over a HashMap in Java is essential when you need to manipulate or perform operations on the key-value pairs. In this article, we have explored two common methods for iterating over a HashMap using entrySet() and keySet().

Remember to choose the appropriate method depending on your specific use case.