6. The Enhanced For Loop
The enhanced for loop iterates over any Iterable or array cleanly, but it cannot provide an index, cannot remove elements safely, and iterates a copy of the loop variable.
Explanation
The enhanced for loop (for (Type x : collection)) is syntactic sugar over Iterator. For arrays, the compiler generates a standard indexed loop; for Iterable implementations, it calls iterator() and loops with hasNext()/next().
Key limitations: you cannot remove elements during iteration using the loop variable — call iterator.remove() via an explicit Iterator, or use collection.removeIf(predicate) (Java 8+). You also do not get the index automatically; if you need both the value and the index, use a classic for (int i = 0; ...) loop.
Mutating the loop variable (x = something) only changes the local copy, not the original element in the collection — a common beginner mistake with primitives. For objects, you can still mutate the object's state via its methods, but reassigning x does nothing to the collection.
Example
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
public class EnhancedForLoop {
public static void main(String[] args) {
List<String> names = new ArrayList<>(List.of("Alice", "Bob", "Charlie"));
// Basic enhanced for
for (String name : names) {
System.out.println(name);
}
// WRONG: ConcurrentModificationException
// for (String name : names) {
// if (name.startsWith("B")) names.remove(name); // throws!
// }
// CORRECT: removeIf (Java 8+)
names.removeIf(n -> n.startsWith("B"));
System.out.println("After removeIf: " + names); // [Alice, Charlie]
// CORRECT: explicit Iterator for remove
List<Integer> nums = new ArrayList<>(List.of(1, 2, 3, 4, 5));
Iterator<Integer> it = nums.iterator();
while (it.hasNext()) {
if (it.next() % 2 == 0) it.remove();
}
System.out.println("Odds only: " + nums); // [1, 3, 5]
// Need index? Use classic for
String[] arr = {"a", "b", "c"};
for (int i = 0; i < arr.length; i++) {
System.out.println(i + ": " + arr[i]);
}
}
}