Resizable lists and the Collections Framework.
✍️ 2 exercises in this lessonThe Collections Framework provides ready-made data structures. ArrayList is a resizable array:
List<String> list = new ArrayList<>();add(), get(i), set(i, v), remove(), size(), contains()Collections.sort(list) or list.sort(...)List.of(...) creates an unmodifiable list.Collections hold objects, so primitives are wrapped: Integer, Double, Boolean.
Mastering Java ArrayList & Collections helps you write clean and reliable Java code. Follow standard conventions, test edge cases, and keep logic simple. Try running the code example below and complete the exercises to build confidence.
import java.util.*;
public class Main {
public static void main(String[] args) {
List<String> cities = new ArrayList<>();
cities.add("Lahore");
cities.add("Karachi");
cities.add("Islamabad");
cities.remove("Karachi");
cities.add(0, "Peshawar");
Collections.sort(cities);
System.out.println(cities);
System.out.println("Size: " + cities.size());
System.out.println(cities.contains("Lahore"));
List<Integer> nums = new ArrayList<>(List.of(5, 3, 9));
nums.sort(Comparator.reverseOrder());
System.out.println(nums);
}
}[Islamabad, Lahore, Peshawar] Size: 3 true [9, 5, 3]
Check what you learned in “Java ArrayList & Collections”.
Add an item to the list.
cities.("Lahore");
Which interface does ArrayList implement?
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