LinkedList as a FIFO Queue and Queue Interface

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LinkedList as a FIFO Queue

The java.util.LinkedList class, while implementing java.util.List is a general-purpose implementation of java.util.Queue interface too operating on a FIFO (First In, First Out) principle.

In the example below, with offer() method, the elements are inserted into the LinkedList. This insertion operation is called enqueue. In the while loop below, the elements are removed from the Queue based on FIFO. This operation is called dequeue.

import java.util.*;
 
public class QueueExample {
    public static void main(String[] args) {
        Queue<String> newQueue = new LinkedList<>();
        newQueue.offer("apple");
        newQueue.offer("banana");
        newQueue.offer("orange");
        newQueue.offer("grape");
        newQueue.offer("melon");
 
        while (!newQueue.isEmpty()) {
            System.out.println(newQueue.poll());
        }
    }
}

Output

apple
banana
orange
grape
melon

As seen in the output, the first inserted element "first element" is removed firstly, "second element" is removed in the second place etc

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Queue Interface

Basics

A Queue is a collection for holding elements prior to processing. Queues typically, but not necessarily, order elements in a FIFO (first-in-first-out) manner.

Head of the queue is the element that would be removed by a call to remove or poll. In a FIFO queue, all new elements are inserted at the tail of the queue.

The Queue Interface

public interface Queue<E> extends Collection<E> {
    boolean add(E e);
    boolean offer(E e);
    E remove();
    E poll();
    E element();
    E peek();
}

Each Queue method exists in two forms:

• one throws an exception if the operation fails;
• other returns a special value if the operation fails (either null or false depending on the operation.

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Basic Programs

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Date Class

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Queues and Deques

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• LinkedList as a FIFO Queue and Queue Interface
• Dequeue Interface

Enums

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Properties Class

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Interfaces

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Regular Expressions

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Java Floating Point Operations

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Currency and Money

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Object Cloning

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Recursion

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Converting to and from Strings

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Random Number Generation

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Autoboxing

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