Stacks and Queues (Basic Data Structures)

This lesson covers implementing a stack and a queue in Java, so you understand how to pick the right way to add and remove data for the job. It's for anyone searching "Java Deque stack queue usage."

A stack is "last in, first out," and a queue is "first in, first out." It helps to picture the difference between "a stack of books" and "a line of people."

The example uses a double-ended queue, Deque<String>, showing it act as a stack with push() and pop(), and as a queue with offer() and poll(). One flexible data structure can play both roles.

A common early mistake is not tracking which methods to call for stack behavior versus queue behavior. Even with the same Deque type, you need to correctly choose the right methods for your purpose.

In real projects, the mechanism that manages function calls is itself built on a stack — an important data structure that connects to core computer science concepts.

📖 Reference code

Deque<String> stack = new ArrayDeque<>();
stack.push("A");
stack.push("B");
System.out.println(stack.pop());

Deque<String> queue = new ArrayDeque<>();
queue.offer("A");
queue.offer("B");
System.out.println(queue.poll());

✍️ Your code

Type your code, then press "Run"

🧪 This site can't compile or run Java directly, so it checks on the spot whether what you typed matches the reference code (scoring happens entirely in your browser — nothing is sent anywhere).