java collection 取第一个

List<String> list = new ArrayList<>();
list.add("Element 1");
list.add("Element 2");

if (!list.isEmpty()) {
    String firstElement = list.get(0);
    System.out.println("First element: " + firstElement);
}

Queue<String> queue = new LinkedList<>();
queue.add("Element 1");
queue.add("Element 2");

if (!queue.isEmpty()) {
    String firstElement = queue.peek();
    System.out.println("First element: " + firstElement);
}

Set<String> set = new HashSet<>();
set.add("Element 1");
set.add("Element 2");

if (!set.isEmpty()) {
    List<String> list = new ArrayList<>(set);
    String firstElement = list.get(0);
    System.out.println("First element: " + firstElement);
}