Java Data Structure Cheat Sheet - Queue

Queue is an interface in Java.

There are multiple implementation choices, but using LinkedList is common and performs as the usual queue as expected.

https://docs.oracle.com/javase/8/docs/api/java/util/Queue.html

Main methods are:

• boolean add(E e)
• E element()
• E remove()

and there exists the alternative ones as:

• boolean offer(E e)
• E peek()
• E poll()

The first group throws an Exception whereas the second one returns "special value".

They are all O(1).

Example

import java.util.LinkedList;
import java.util.Queue;

public class QueueExample {
  public static void main(String[] args) {
    Queue<Integer> q = new LinkedList<Integer>();

    q.add(1); // or q.offer(1)
    q.add(2);
    q.add(3);

    System.out.println(q.element()); // 1. you can also use q.peek()

    while (!q.isEmpty()) { // isEmpty() is from Collection
      int n = q.remove(); // or q.poll()
      System.out.println(n); // 1, 2, 3
    }
  }
}