Question

I’ve seen a different approach of using the FOR loop like this after create a “List” object type.

List<Focus> focuses = new ArrayList<Focus>();
String my_string = "";
for (Focus obj1 : list_obj_x) {
    my_string += obj1;
}

I don’t understand how this FOR loop works in this situation.

Thanks

Answer 1

The enhanced for loop can be used with any object that implements Iterable<X> and with arrays. It is equivalent to using a for loop with an iterator (in case of an iterable):

// with Iterables:

Iterable<String> iterableStrings = getListOfStrings();

// standard for loop
for (Iterator<String> it = iterableStrings.iterator(); it.hasNext(); ) {
   String s = it.next();
   System.out.println(s);
}

// enhanced for loop
for (String s : iterableStrings) {
   System.out.println(s);
}

// with arrays:

String[] stringArray = getStringArray();

// standard for loop
for (int i = 0; i < stringArray.length; i++) {
   String s = stringArray[i];
   System.out.println(s);
}

// enhanced for loop
for (String s : stringArray) {
   System.out.println(s);
}

It’s usage is not limited to “indexed collections” like lists and arrays.

Reference

JLS 14.14.2