LinkedList in Java

LinkedList stores elements in nodes, where each node holds a value and pointers to the next and previous nodes. Unlike ArrayList which stores everything in one continuous array, LinkedList elements can be anywhere in memory — connected only through pointers.

This structure means inserting or removing at the front or middle is fast (just reroute pointers), but accessing a specific index is slow (you must follow the chain from the start).

Creating and Using LinkedList

Run this example to see its output.

Line by line:

• list.addFirst("Apple") — inserts at the front in O(1). Very fast.
• list.add(2, "Blueberry") — insert at index 2: LinkedList must walk to that position first (O(n)).
• list.getFirst() and list.getLast() — O(1) access to both ends.
• list.get(1) — O(n) because it walks from the head.

LinkedList as a Queue (FIFO)

Run this example to see its output.

offer() adds to the tail. poll() removes from the head. This is FIFO — first in, first out. Perfect for queuing tasks, requests, or events.

LinkedList as a Deque (Both Ends)

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Deque (double-ended queue) allows adding and removing from both ends. Useful for sliding window problems, undo/redo stacks, and browser history.

LinkedList vs ArrayList — When to Choose

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Choose ArrayList when: you mostly read by index, or add to the end. Choose LinkedList when: you frequently add/remove from both ends, or use it as a queue/deque.

In most real programs, ArrayList is faster because modern CPUs cache contiguous memory very efficiently. Use LinkedList specifically for queue/deque behaviour.

Common Mistake: Using LinkedList for Random Access

If you find yourself using list.get(i) in a loop with LinkedList, switch to ArrayList.

Practice Task

Task: Simulate a printer queue using LinkedList as a Queue<String>. Add 4 print jobs. Print the total number in the queue. Process (poll) each job one by one and print "Printing: [job]". After each print, show how many jobs remain.

Hint: Use queue.size() before and after polling. The loop condition is !queue.isEmpty().

Solution:

Run this example to see its output.

What to observe: poll() removes and returns the first item each time — the queue shrinks. peek() would let you look at the front without removing. Try replacing Queue<String> with Deque<String> and add addFirst() — you can jump a job to the front of the queue.