forEach loop Java 8 for Map entry set

Maybe the best way to answer the questions like "which version is faster and which one shall I use?" is to look to the source code:

map.forEach() - from Map.java

default void forEach(BiConsumer<? super K, ? super V> action) {
    Objects.requireNonNull(action);
    for (Map.Entry<K, V> entry : entrySet()) {
        K k;
        V v;
        try {
            k = entry.getKey();
            v = entry.getValue();
        } catch(IllegalStateException ise) {
            // this usually means the entry is no longer in the map.
            throw new ConcurrentModificationException(ise);
        }
        action.accept(k, v);
    }
}

javadoc

map.entrySet().forEach() - from Iterable.java

default void forEach(Consumer<? super T> action) {
    Objects.requireNonNull(action);
    for (T t : this) {
        action.accept(t);
    }
}

javadoc

This immediately reveals that map.forEach() is also using Map.Entry internally. So I would not expect any performance benefit in using map.forEach() over the map.entrySet().forEach(). So in your case the answer really depends on your personal taste :)

For the complete list of differences please refer to the provided javadoc links. Happy coding!

Read the javadoc: Map<K, V>.forEach() expects a BiConsumer<? super K,? super V> as argument, and the signature of the BiConsumer<T, U> abstract method is accept(T t, U u).

So you should pass it a lambda expression that takes two inputs as argument: the key and the value:

map.forEach((key, value) -> {
    System.out.println("Key : " + key + " Value : " + value);
});

Your code would work if you called forEach() on the entry set of the map, not on the map itself:

map.entrySet().forEach(entry -> {
    System.out.println("Key : " + entry.getKey() + " Value : " + entry.getValue());
});