How does the Java 'for each' loop work?

Question

Consider:

List<String> someList = new ArrayList<String>();
// add "monkey", "donkey", "skeleton key" to someList

for (String item : someList) {
    System.out.println(item);
}

What would the equivalent for loop look like without using the for each syntax?

Answer 1

Prior to Java 8, you need to use the following:

Iterator<String> iterator = someList.iterator();

while (iterator.hasNext()) {
    String item = iterator.next();
    System.out.println(item);
}

However, with the introduction of Streams in Java 8 you can do same thing in much less syntax. For example, for your someList you can do:

someList.stream().forEach(System.out::println);

You can find more about streams here.

Answer 2

The for-each loop in Java uses the underlying iterator mechanism. So it's identical to the following:

Iterator<String> iterator = someList.iterator();

while (iterator.hasNext()) {
  String item = iterator.next();
  System.out.println(item);
}