Java LinkedList

In this page:

Introduction to LinkedList
LinkedList as a Queue / Deque
Inserting and Removing Nodes
Iterating over LinkedList
ArrayList vs LinkedList

Introduction to LinkedList

LinkedList implements List using a doubly-linked chain of nodes rather than a contiguous array, so each element only needs to know its neighbors, not a fixed memory block.

Example: Introduction to LinkedList

java

import java.util.LinkedList;
public class Main {
	public static void main(String[] args) {
		LinkedList<String> list = new LinkedList<>(); // chain of nodes
		list.add("a");
		list.add("b");
		System.out.println(list);
	}
}

LinkedList as a Queue / Deque

Because it also implements Deque, LinkedList can be used directly as a queue (FIFO, via offer()/poll()) or a stack (LIFO, via push()/pop()) without needing a separate data structure.

Example: LinkedList as a Queue / Deque

java

import java.util.LinkedList;
public class Main {
	public static void main(String[] args) {
		LinkedList<Integer> queue = new LinkedList<>();
		queue.offer(1); // FIFO
		queue.offer(2);
		System.out.println(queue.poll());
		LinkedList<Integer> stack = new LinkedList<>();
		stack.push(1); // LIFO
		stack.push(2);
		System.out.println(stack.pop());
	}
}

Inserting and Removing Nodes

Inserting or removing a node is fast (O(1)) once you already have a reference to that position, since it's just a matter of relinking neighboring pointers — no shifting of other elements required.

Example: Inserting and Removing Nodes

java

import java.util.LinkedList;
public class Main {
	public static void main(String[] args) {
		LinkedList<String> list = new LinkedList<>();
		list.add("a");
		list.add("c");
		list.add(1, "b"); // fast insert once at that position
		System.out.println(list);
	}
}

Iterating over LinkedList

Iterating a LinkedList works the same way syntactically as an ArrayList (for-each or Iterator), but random access by index is slow (O(n)) since the list has to walk node-by-node from one end to reach a given position.

Example: Iterating over LinkedList

java

import java.util.LinkedList;
public class Main {
	public static void main(String[] args) {
		LinkedList<String> list = new LinkedList<>();
		list.add("a");
		list.add("b");
		for (String item : list) { // same syntax as ArrayList
			System.out.println(item);
		}
	}
}

ArrayList vs LinkedList

Choose ArrayList when you mostly read by index; choose LinkedList when you mostly insert/remove at the ends or in the middle via an iterator — picking the wrong one for your access pattern can hurt performance significantly.

Example: ArrayList vs LinkedList

java

import java.util.ArrayList;
import java.util.LinkedList;
public class Main {
	public static void main(String[] args) {
		ArrayList<Integer> arrayList = new ArrayList<>(); // best for index reads
		LinkedList<Integer> linkedList = new LinkedList<>(); // best for insert/remove at ends
		arrayList.add(1);
		linkedList.addFirst(1);
		System.out.println(arrayList.get(0));
		System.out.println(linkedList.getFirst());
	}
}

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Java LinkedList

Introduction to LinkedList

LinkedList as a Queue / Deque

Inserting and Removing Nodes

Iterating over LinkedList

ArrayList vs LinkedList

Chapter Quiz — Complete all 17 topics to unlock

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