How to for each the hashmap?

Smart iteration techniques

Let's get our hands dirty and dig deep into various ways to iterate a Hashmap, addressing different scenarios and efficiency.

Invoke Java 8 magic

From Java 8, use forEach with lambda expressions to subtly slide through entries:

map.forEach((key, value) -> {
    // Let's hangout with key and value
});


Stream for order!

When order matters, trust the combination of stream() and forEachOrdered. It's like getting sushi in a conveyor belt.

map.entrySet().stream().forEachOrdered(e ->
    System.out.println("Key: " + e.getKey() + ", Value: " + e.getValue())
);


Performance matters, go parallel

For large collections, parallelStream() could potentially enhance performance, kinda like having extra hands to sort the laundry.

map.entrySet().parallelStream().forEach(e ->
    System.out.println("Key: " + e.getKey() + ", Value: " + e.getValue())
);


Note: It's like eating the elephant, piece by piece. Use wisely as the overhead might not always lead to performance gains.

Nesting, it's not just for birds

For nested HashMaps, nested for-each loops come to the rescue:

for (Map.Entry<K, Map<K,V>> outerEntry : nestedMap.entrySet()) {
    K outerKey = outerEntry.getKey();
    Map<K,V> innerMap = outerEntry.getValue(); // Let's dive in!
    for (Map.Entry<K, V> innerEntry : innerMap.entrySet()) {
        K innerKey = innerEntry.getKey();
        V innerValue = innerEntry.getValue();
        // Let's dance with inner keys and values
    }
}


Winning against special scenarios

Life's not always straightforward. Hence, we've got some special techniques for those curveball scenarios.

Dodging ConcurrentModificationException

To avoid a crash mid-party (ConcurrentModificationException), party with the Iterator:

Iterator<Map.Entry<K, V>> it = map.entrySet().iterator();
while (it.hasNext()) {
    Map.Entry<K, V> entry = it.next();
    // It's safer to modify map with the iterator's hipster remove method
}


Just the values, you fancy!

To cartwheel over values skipping the keys, use the values() method:

for (V value : map.values()) {
    System.out.println("Value: " + value);
}


Element of surprise using Random

Amalgamate fun with randomness into your iteration logic using Java's Random:

Random rand = new Random();
map.forEach((key, value) -> {
    if (rand.nextBoolean()) { // Nothing like a small game of heads or tails
        // Trigger random task here
    }
});


Populate UI, impress users

Whip up sleek UI components like a ComboBox, using values. Just remember to iterate within the safe house (UI event dispatch thread):

map.values().forEach(value -> comboBox.addItem(value));


For masterclass perfection, know the difference between forEach and forEachOrdered and use wisely according to your taste in order and performance.