java collections

class User { public int userId; public String username; public String address; public User(int userId, String username, String address) { this.userId = userId; this.username = username; this.address = address; } } class UserIdComparator implements Comparator<User> { public int compare(User user1, User user2) { if (user1.userId == user2.userId) { return 0; } else if (user1.userId >…

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public int compareTo(Object obj) class Test { public static void main(String[] args) { List<String> list = new ArrayList<>(); list.add(“Python”); list.add(“Java”); list.add(“JavaScript”); list.add(“Ruby”); list.add(“Kotlin”); System.out.println(“Before sorting:”); System.out.println(list); // sorting the list Collections.sort(list); System.out.println(“After sorting:”); System.out.println(list); } } Output: Before sorting: [Python, Java, JavaScript, Ruby, Kotlin] After sorting: [Java, JavaScript, Kotlin, Python, Ruby] Sorting the array of…

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Queue queue1 = new LinkedList(); Queue queue2 = new PriorityQueue(); class Test { public static void main(String[] args) { Queue<String> queue = new LinkedList(); queue.offer(“Steve”); queue.offer(“Megan”); queue.offer(“Ryan”); queue.offer(“Melissa”); System.out.println(queue); } } Output: [Steve, Megan, Ryan, Melissa]   We can also use the add(Object o) method to add elements to the Queue. In this example, we will…

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HashMap<K, V> map = new HashMap<>(); Map<Integer, String> map = new HashMap<>(); class Test { public static void main(String[] args) { Map<Integer, String> map = new HashMap<>(); map.put(1, “Java”); map.put(7, “Python”); map.put(10, “Ruby”); map.put(3, “Kotlin”); System.out.println(map); } } Output: {1=Java, 3=Kotlin, 7=Python, 10=Ruby} class Test { public static void main(String[] args) { Map<Integer, String> map…

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HashSet<String> set = new HashSet<>(); Set<String> set = new HashSet<>(); class Test { public static void main(String[] args) { Set<String> set = new HashSet<>(); set.add(“Java”); set.add(“Kotlin”); set.add(“Python”); set.add(“Ruby”); System.out.println(set); } } Output: [Java, Ruby, Kotlin, Python] class Test { public static void main(String[] args) { Set<String> set = new HashSet<>(); set.add(“Kotlin”); set.add(“Java”); set.add(“Ruby”); set.add(“Python”); Set<String>…

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LinkedList<String> list = new LinkedList<>(); List<Integer> list = new LinkedList<>(); class Test { public static void main(String[] args) { List<String> list = new LinkedList<>(); list.add(“Steve”); list.add(“Megan”); list.add(“Melissa”); list.add(“Ryan”); System.out.println(list); } } Output: [Steve, Megan, Melissa, Ryan] class Test { public static void main(String[] args) { List<String> list = new LinkedList<>(); list.add(“Steve”); list.add(“Megan”); list.add(“Melissa”); list.add(“Ryan”); List<String>…

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ArrayList<String> list = new ArrayList<>(); List<Integer> list = new ArrayList<>(); class Test { public static void main(String[] args) { List<String> list = new ArrayList<>(); list.add(“Steve”); list.add(“Megan”); list.add(“Melissa”); list.add(“Ryan”); System.out.println(list); } } Output: [Steve, Megan, Melissa, Ryan]   Using the addAll() method, we can add all the elements of an existing list to the newly created…

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Iterator<T> iterator()   Method Description   public boolean add(E e) It is used to insert an element in this collection.   public boolean addAll(Collection<? extends E> c) It is used to insert the specified collection elements in the invoking collection.   public boolean remove(Object element) It is used to delete an element from the collection.…

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