Java - Enhanced for (For-Each) Loop

Java SE 8 Documentation: The For-Each Loop

Enhanced for (For-Each) Loop

Java의 Enhanced for Loop는 Java 5에서 도입된 새로운 반복 구문

• 배열 또는 Iterable 인터페이스를 구현하는 클래스(java SE 17)
• 코드를 간결하게, 가독성을 향상

기존의 for 루프와 비교

// 기존의 for 루프
int[] numbers = {1, 2, 3, 4, 5};
for (int i = 0; i < numbers.length; i++) {
    System.out.println(numbers[i]);
}

// Enhanced for 루프 (foreach)
int[] numbers = {1, 2, 3, 4, 5};
for (int number : numbers) {
    System.out.println(number);
}

Iterator 사용 시 가독성

List suits = ...;
List ranks = ...;
List sortedDeck = new ArrayList();

// BROKEN - throws NoSuchElementException!
for (Iterator i = suits.iterator(); i.hasNext(); )
    for (Iterator j = ranks.iterator(); j.hasNext(); )
        sortedDeck.add(new Card(i.next(), j.next()));

여기서 하위 반복문의 i.next() 호출이 너무 많고 가독성이 떨어진다.

for (Suit suit : suits)
    for (Rank rank : ranks)
        sortedDeck.add(new Card(suit, rank));

Java SE 8 Documentation: The For-Each Loop The program needs access to the iterator in order to remove the current element. The for-each loop hides the iterator, so you cannot call remove. Therefore, the for-each loop is not usable for filtering. Similarly it is not usable for loops where you need to replace elements in a list or array as you traverse it. Finally, it is not usable for loops that must iterate over multiple collections in parallel.