Mastering Java Collections: A Comprehensive Guide (Part 1)

Java Collections Framework (JCF) provides powerful data structures that simplify complex programming tasks. In this blog series, we will explore all collection types and their methods in detail, ensuring you skip none! 1. ArrayList (java.util.ArrayList) Overview ArrayList is a resizable array implementation of the List interface. It allows random access, dynamic resizing, and provides fast read operations (O(1)) but slower insertions/deletions (O(n)). Constructors ArrayList list = new ArrayList(); // Default ArrayList list2 = new ArrayList(20); // With initial capacity ArrayList list3 = new ArrayList(list2); // Copying another list Core Methods Adding Elements list.add(10); // Appends element at the end list.add(1, 20); // Inserts 20 at index 1 Removing Elements list.remove(1); // Removes element at index 1 list.remove(Integer.valueOf(10)); // Removes first occurrence of 10 list.clear(); // Removes all elements Retrieving Elements int val = list.get(0); // Retrieves the first element Updating Elements list.set(0, 99); // Updates the first element to 99 Searching Elements boolean exists = list.contains(99); // Returns true if 99 exists int index = list.indexOf(99); // Returns index of first occurrence int lastIndex = list.lastIndexOf(99); // Returns last occurrence Checking Size and Emptiness int size = list.size(); // Returns number of elements boolean isEmpty = list.isEmpty(); // Checks if empty Iteration for (Integer num : list) { System.out.println(num); } Conversion Object[] arr = list.toArray(); // Converts to Object array Integer[] intArr = list.toArray(new Integer[0]); // Converts to Integer array Sorting list.sort(Comparator.naturalOrder()); // Sorts in ascending order 2. LinkedList (java.util.LinkedList) Overview A LinkedList is a doubly linked list implementation of List and Deque. It allows fast insertions and deletions (O(1)) but slower access (O(n)). Constructors LinkedList linkedList = new LinkedList(); Core Methods Adding Elements linkedList.add("Apple"); // Adds at end linkedList.addFirst("Orange"); // Adds at beginning linkedList.addLast("Banana"); // Adds at end Removing Elements linkedList.remove(); // Removes first element linkedList.remove(1); // Removes element at index 1 linkedList.removeFirst(); // Removes first element linkedList.removeLast(); // Removes last element Retrieving Elements String first = linkedList.getFirst(); // Gets first element String last = linkedList.getLast(); // Gets last element Checking Size and Emptiness int size = linkedList.size(); boolean isEmpty = linkedList.isEmpty(); Iteration for (String item : linkedList) { System.out.println(item); } Queue Methods (Inherited from Deque) linkedList.offer("Grapes"); // Adds element at end String head = linkedList.poll(); // Retrieves and removes first element String peekElement = linkedList.peek(); // Retrieves first element without removing 3. Queue (java.util.Queue) Overview A Queue follows FIFO (First-In-First-Out) principle. It is implemented by LinkedList and PriorityQueue. Core Methods Adding and Removing Elements Queue queue = new LinkedList(); queue.offer(10); // Adds 10 to the queue queue.offer(20); Retrieving Elements int first = queue.poll(); // Retrieves and removes head element int head = queue.peek(); // Retrieves head without removing Checking Size and Emptiness int size = queue.size(); boolean isEmpty = queue.isEmpty(); 4. Stack (java.util.Stack) Overview A Stack follows LIFO (Last-In-First-Out) principle. It extends Vector. Core Methods Adding and Removing Elements Stack stack = new Stack(); stack.push(10); // Pushes element onto stack stack.push(20); Retrieving Elements int top = stack.peek(); // Returns top element without removing int popped = stack.pop(); // Removes and returns top element Checking if Empty boolean isEmpty = stack.empty(); Searching Elements int position = stack.search(10); // Returns 1-based position Conclusion This concludes Part 1 of our Java Collections deep dive. We covered ArrayList, LinkedList, Queue, and Stack, exploring all their methods with examples. Stay tuned for Part 2, where we will cover Deque, HashSet, and HashMap in detail!

Mar 26, 2025 - 19:16

Mastering Java Collections: A Comprehensive Guide (Part 1)

Java Collections Framework (JCF) provides powerful data structures that simplify complex programming tasks. In this blog series, we will explore all collection types and their methods in detail, ensuring you skip none!

1. ArrayList (`java.util.ArrayList`)

Overview

ArrayList is a resizable array implementation of the List interface. It allows random access, dynamic resizing, and provides fast read operations (O(1)) but slower insertions/deletions (O(n)).

Constructors

ArrayList<Integer> list = new ArrayList<>(); // Default
ArrayList<Integer> list2 = new ArrayList<>(20); // With initial capacity
ArrayList<Integer> list3 = new ArrayList<>(list2); // Copying another list

Core Methods

Adding Elements

list.add(10); // Appends element at the end
list.add(1, 20); // Inserts 20 at index 1

Removing Elements

list.remove(1); // Removes element at index 1
list.remove(Integer.valueOf(10)); // Removes first occurrence of 10
list.clear(); // Removes all elements

Retrieving Elements

int val = list.get(0); // Retrieves the first element

Updating Elements

list.set(0, 99); // Updates the first element to 99

Searching Elements

boolean exists = list.contains(99); // Returns true if 99 exists
int index = list.indexOf(99); // Returns index of first occurrence
int lastIndex = list.lastIndexOf(99); // Returns last occurrence

Checking Size and Emptiness

int size = list.size(); // Returns number of elements
boolean isEmpty = list.isEmpty(); // Checks if empty

Iteration

for (Integer num : list) { System.out.println(num); }

Conversion

Object[] arr = list.toArray(); // Converts to Object array
Integer[] intArr = list.toArray(new Integer[0]); // Converts to Integer array

Sorting

list.sort(Comparator.naturalOrder()); // Sorts in ascending order

2. LinkedList (`java.util.LinkedList`)

Overview

A LinkedList is a doubly linked list implementation of List and Deque. It allows fast insertions and deletions (O(1)) but slower access (O(n)).

Constructors

LinkedList<String> linkedList = new LinkedList<>();

Core Methods

Adding Elements

linkedList.add("Apple"); // Adds at end
linkedList.addFirst("Orange"); // Adds at beginning
linkedList.addLast("Banana"); // Adds at end

Removing Elements

linkedList.remove(); // Removes first element
linkedList.remove(1); // Removes element at index 1
linkedList.removeFirst(); // Removes first element
linkedList.removeLast(); // Removes last element

Retrieving Elements

String first = linkedList.getFirst(); // Gets first element
String last = linkedList.getLast(); // Gets last element

Checking Size and Emptiness

int size = linkedList.size();
boolean isEmpty = linkedList.isEmpty();

Iteration

for (String item : linkedList) { System.out.println(item); }

Queue Methods (Inherited from Deque)

linkedList.offer("Grapes"); // Adds element at end
String head = linkedList.poll(); // Retrieves and removes first element
String peekElement = linkedList.peek(); // Retrieves first element without removing

3. Queue (`java.util.Queue`)

Overview

A Queue follows FIFO (First-In-First-Out) principle. It is implemented by LinkedList and PriorityQueue.

Core Methods

Adding and Removing Elements

Queue<Integer> queue = new LinkedList<>();
queue.offer(10); // Adds 10 to the queue
queue.offer(20);

Retrieving Elements

int first = queue.poll(); // Retrieves and removes head element
int head = queue.peek(); // Retrieves head without removing

Checking Size and Emptiness

int size = queue.size();
boolean isEmpty = queue.isEmpty();

4. Stack (`java.util.Stack`)

Overview

A Stack follows LIFO (Last-In-First-Out) principle. It extends Vector.

Core Methods

Adding and Removing Elements

Stack<Integer> stack = new Stack<>();
stack.push(10); // Pushes element onto stack
stack.push(20);

Retrieving Elements

int top = stack.peek(); // Returns top element without removing
int popped = stack.pop(); // Removes and returns top element

Checking if Empty

boolean isEmpty = stack.empty();

Searching Elements

int position = stack.search(10); // Returns 1-based position

Conclusion

This concludes Part 1 of our Java Collections deep dive. We covered ArrayList, LinkedList, Queue, and Stack, exploring all their methods with examples. Stay tuned for Part 2, where we will cover Deque, HashSet, and HashMap in detail!