[Java] Queue, Deque

When I was studying Java Gold, it came out, so I scribbled it.

Queue<E> Inherit Collection \ . That is, it is a thing for using multiple data together like an array. Then, when I looked up the word Queue on a certain English translation site to see what makes it different from other collections,

** Rows (people and vehicles waiting for their turn) **

And that. The inside of () is miso.

In other words, it has a data structure called "FIFO (First-in-First-out)" that allows you to retrieve the first thing you put in. People who are waiting for their turn will come first, and those who are in line will come first.

That's why it's sometimes called a "queue".

However, it does not mean that it has to be a separate FIFO implementation.

Method

QueueTest.java

import java.util.Queue;
import java.util.ArrayDeque;

public class QueueTest {
    public void myQueue() {
        Queue<Integer> queueTest = new ArrayDeque<Integer>();
        for(int i=0; i < 10; i++) {
            //Insert value into queue
            queueTest.add(i);
        }
        //Insert value into queue
        queueTest.offer(100);

        System.out.println(queueTest);
        
        //Extract the beginning
        Integer r = queueTest.remove();
        System.out.println("remove value: " + r);

        //See top
        System.out.println(queueTest.element());

        //Extract the beginning
        Integer p = queueTest.poll();
        System.out.println("poll value: " + p);

        //See top
        System.out.println(queueTest.peek());

        System.out.println(queueTest);
    }
}

Execution result:

[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 100]
remove value: 0
1
poll value: 1
2
[2, 3, 4, 5, 6, 7, 8, 9, 100]

Deque<E> Inherit Queue \ . The official name is "Double Ended Queue" As the name implies, it is a queue that allows you to insert and delete elements from both ends.

By the way, Deque seems to be read as "deck". I thought, "Isn't it'dequeue'...", but with "dequeue" which means "operation to retrieve data" It was a mess. There must be someone who made the same mistake.

Method

Why isn't it the reference elementFirst / Last for the exception throw ...

DequeTest.java

import java.util.Deque;
import java.util.ArrayDeque;

public class DequeTest {
    public void myDeque() {
        Deque<Integer> dequeTest = new ArrayDeque<Integer>();
        for(int i=0; i < 10; i++) {
            //Insert value into queue from beginning
            dequeTest.addFirst(i);
        }

        System.out.println(dequeTest);

        //Extract the end
        Integer r = dequeTest.removeLast();
        System.out.println("remove value: " + r);

        //See end
        System.out.println(dequeTest.getLast());

        //Extract the beginning
        Integer p = dequeTest.pollFirst();
        System.out.println("poll value: " + p);

        //See top
        System.out.println(dequeTest.peekFirst());

        System.out.println(dequeTest);
    }
}

Execution result:

[9, 8, 7, 6, 5, 4, 3, 2, 1, 0]
remove value: 0
1
poll value: 9
8
[8, 7, 6, 5, 4, 3, 2, 1]

You can see that the insertion order of the values from 0 to 9 is the reverse of Queue. Since it can be inserted from both directions, it can also be used as a stack that uses the "LIFO (Last-in-First-out) / last-in-first-out method".