How do I efficiently iterate over each entry in a Java Map?

Consider:

Map<String, String> map = ...
for (Map.Entry<String, String> entry : map.entrySet()) {
    System.out.println(entry.getKey() + "/" + entry.getValue());
}

In Java 8 you can do it clean and fast using the new lambdas features:

final long[] i = {0};
map.forEach((k, v) -> i[0] += k + v);