How do I add and retrieve elements from a list on a FIFO basis

In this Q&A, we'll go over how to add and retrieve elements from a Queue on a First In First Out  (FIFO) basis.

Java collections framework provides the Queue interface and multiple concrete implementations.  In this Q&A we'll go over how to achieve it using LinkedList.

LinkedList is also a Queue.  You can add or poll for elements using it.

In the example below, please note the difference between the poll() and remove() methods.

import java.util.LinkedList;

import java.util.NoSuchElementException;

public class QueueTest {

    public static void fifoQueue() {

        LinkedList<Integer> li = new LinkedList<>();

        for(int i = 0; i < 1000; ++i )

            li.add(i);

        for(int i = 0; i < 1000; ++i ) {

            Integer i1 = li.poll();

            assert ( i1 == i);

        }

        // returns null if there are no elements

        Integer i2 = li.poll();

        assert(  i2 == null );

        int s = li.size();

        assert( s == 0 );

        try {

            // throws an exception if there are no elements

            Integer r = li.remove();

        } catch( Exception e ) {

            assert( e instanceof NoSuchElementException);

            System.out.println("NoSuchElementException assertion passed");

        }

        System.out.println("all assertions passed");

    }

    public static void main( String[] args ) {

        fifoQueue();

    }

}