Queue<String> queue = new LinkedList<>();  // Queue interface uses LL implementation
queue.add("John");
queue.add("Jane");
queue.add("Bob");
// Collections has a toArray convertion
Object[] arr = queue.toArray();

// Empty queue
System.out.println("Empty Queue");
while (queue.size() > 0) // Interate while size
    System.out.println(queue.remove());

// Iterate of array
System.out.println("Iterate over Array");
for (Object a : arr) // Type is Object from convertion
    System.out.println(a);

/* This is wrapper class...
 Objective would be to push more functionality into this Class to enforce consistent definition
 */
public abstract class Generics {
	public final String masterType = "Generic";
	private String type;	// extender should define their data type

	// generic enumerated interface
	public interface KeyTypes {
		String name();
	}
	protected abstract KeyTypes getKey();  	// this method helps force usage of KeyTypes

	// getter
	public String getMasterType() {
		return masterType;
	}

	// getter
	public String getType() {
		return type;
	}

	// setter
	public void setType(String type) {
		this.type = type;
	}
	
	// this method is used to establish key order
	public abstract String toString();

	// static print method used by extended classes
	public static void print(Generics[] objs) {
		// print 'Object' properties
		System.out.println(objs.getClass() + " " + objs.length);

		// print 'Generics' properties
		if (objs.length > 0) {
			Generics obj = objs[0];	// Look at properties of 1st element
			System.out.println(
					obj.getMasterType() + ": " + 
					obj.getType() +
					" listed by " +
					obj.getKey());
		}

		// print "Generics: Objects'
		for(Object o : objs)	// observe that type is Opaque
			System.out.println(o);

		System.out.println();
	}
}

public class Alphabet extends Generics {
	// Class data
	public static KeyTypes key = KeyType.title;  // static initializer
	public static void setOrder(KeyTypes key) {Alphabet.key = key;}
	public enum KeyType implements KeyTypes {title, letter}
	private static final int size = 26;  // constant used in data initialization

	// Instance data
	private final char letter;
	
	/*
	 * single letter object
	 */
	public Alphabet(char letter)
	{
		this.setType("Alphabet");
		this.letter = letter;
	}

	/* 'Generics' requires getKey to help enforce KeyTypes usage */
	@Override
	protected KeyTypes getKey() { return Alphabet.key; }

	/* 'Generics' requires toString override
	 * toString provides data based off of Static Key setting
	 */
	@Override
	public String toString()
	{
		String output="";
		if (KeyType.letter.equals(this.getKey())) {
			output += this.letter;
		} else {
			output += super.getType() + ": " + this.letter;
		}
		return output;
	}

	// Test data initializer for upper case Alphabet
	public static Alphabet[] alphabetData()
	{
		Alphabet[] alphabet = new Alphabet[Alphabet.size];
		for (int i = 0; i < Alphabet.size; i++)
		{
			alphabet[i] = new Alphabet( (char)('A' + i) );
		} 	
		return alphabet;
	}
	
	/* 
	 * main to test Animal class
	 */
	public static void main(String[] args)
	{
		// Inheritance Hierarchy
		Alphabet[] objs = alphabetData();

		// print with title
		Alphabet.setOrder(KeyType.title);
		Alphabet.print(objs);

		// print letter only
		Alphabet.setOrder(KeyType.letter);
		Alphabet.print(objs);
	}
	
}
Alphabet.main(null);

public class Animal extends Generics {
	// Class data
	public static KeyTypes key = KeyType.title;  // static initializer
	public static void setOrder(KeyTypes key) { Animal.key = key; }
	public enum KeyType implements KeyTypes {title, name, age, color}

	// Instance data
	private final String name;
	private final int age;
	private final String color;

	/* constructor
	 *
	 */
	public Animal(String name, int age, String color)
	{
		super.setType("Animal");
		this.name = name;
		this.age = age;
		this.color = color;
	}

	/* 'Generics' requires getKey to help enforce KeyTypes usage */
	@Override
	protected KeyTypes getKey() { return Animal.key; }
	
	/* 'Generics' requires toString override
	 * toString provides data based off of Static Key setting
	 */
	@Override
	public String toString()
	{
		String output="";
		if (KeyType.name.equals(this.getKey())) {
			output += this.name;
		} else if (KeyType.age.equals(this.getKey())) {
			output += "00" + this.age;
			output = output.substring(output.length() - 2);
		} else if (KeyType.color.equals(this.getKey())) {
			output += this.color;
		} else {
			output += super.getType() + ": " + this.name + ", " + this.color + ", " + this.age;
		}
		return output;
		
	}

	// Test data initializer
	public static Animal[] animals() {
		return new Animal[]{
				new Animal("Lion", 8, "Gold"),
				new Animal("Pig", 3, "Pink"),
				new Animal("Robin", 7, "Red"),
				new Animal("Cat", 10, "Black"),
				new Animal("Kitty", 1, "Calico"),
				new Animal("Dog", 14, "Brown")
		};
	}
	
	/* main to test Animal class
	 * 
	 */
	public static void main(String[] args)
	{
		// Inheritance Hierarchy
		Animal[] objs = animals();

		// print with title
		Animal.setOrder(KeyType.title);
		Animal.print(objs);

		// print name only
		Animal.setOrder(KeyType.name);
		Animal.print(objs);
	}

}
Animal.main(null);

public class Cupcake extends Generics {
	// Class data
	public static KeyTypes key = KeyType.title;  // static initializer
	public static void setOrder(KeyTypes key) {Cupcake.key = key;}
	public enum KeyType implements KeyTypes {title, flavor, frosting, sprinkles}

	// Instance data
	private final String frosting;
	private final int sprinkles;
	private final String flavor;

	// Constructor
	Cupcake(String frosting, int sprinkles, String flavor)
	{
		this.setType("Cupcake");
		this.frosting = frosting;
		this.sprinkles = sprinkles;
		this.flavor = flavor;
	}

	/* 'Generics' requires getKey to help enforce KeyTypes usage */
	@Override
	protected KeyTypes getKey() { return Cupcake.key; }

	/* 'Generics' requires toString override
	 * toString provides data based off of Static Key setting
	 */
	@Override
	public String toString() {		
		String output="";
		if (KeyType.flavor.equals(this.getKey())) {
			output += this.flavor;
		} else if (KeyType.frosting.equals(this.getKey())) {
			output += this.frosting;
		} else if (KeyType.sprinkles.equals(this.getKey())) {
			output += "00" + this.sprinkles;
			output = output.substring(output.length() - 2);
		} else {
			output = super.getType() + ": " + this.flavor + ", " + this.frosting + ", " + this.sprinkles;
		}
		return output;
	}

	// Test data initializer
	public static Cupcake[] cupcakes() {
		return new Cupcake[]{
				new Cupcake("Red", 4, "Red Velvet"),
			    new Cupcake("Orange", 5, "Orange"),
			    new Cupcake("Yellow", 6, "Lemon"),
			    new Cupcake("Green", 7, "Apple"),
			    new Cupcake("Blue", 8, "Blueberry"),
			    new Cupcake("Purple", 9, "Blackberry"),
			    new Cupcake("Pink", 10, "Strawberry"),
			    new Cupcake("Tan", 11, "Vanilla"),
			    new Cupcake("Brown", 12, "Chocolate"),
		};
	}
	
	public static void main(String[] args)
	{
		// Inheritance Hierarchy
		Cupcake[] objs = cupcakes();

		// print with title
		Cupcake.setOrder(KeyType.title);
		Cupcake.print(objs);

		// print flavor only
		Cupcake.setOrder(KeyType.flavor);
		Cupcake.print(objs);
	}
	
}
Cupcake.main(null);

/**
 *  Implementation of a Double Linked List;  forward and backward links point to adjacent Nodes.
 *
 */

 public class LinkedList<T>
 {
     private T data;
     private LinkedList<T> prevNode, nextNode;
 
     /**
      *  Constructs a new element
      *
      * @param  data, data of object
      * @param  node, previous node
      */
     public LinkedList(T data, LinkedList<T> node)
     {
         this.setData(data);
         this.setPrevNode(node);
         this.setNextNode(null);
     }
 
     /**
      *  Clone an object,
      *
      * @param  node  object to clone
      */
     public LinkedList(LinkedList<T> node)
     {
         this.setData(node.data);
         this.setPrevNode(node.prevNode);
         this.setNextNode(node.nextNode);
     }
 
     /**
      *  Setter for T data in DoubleLinkedNode object
      *
      * @param  data, update data of object
      */
     public void setData(T data)
     {
         this.data = data;
     }
 
     /**
      *  Returns T data for this element
      *
      * @return  data associated with object
      */
     public T getData()
     {
         return this.data;
     }
 
     /**
      *  Setter for prevNode in DoubleLinkedNode object
      *
      * @param node, prevNode to current Object
      */
     public void setPrevNode(LinkedList<T> node)
     {
         this.prevNode = node;
     }
 
     /**
      *  Setter for nextNode in DoubleLinkedNode object
      *
      * @param node, nextNode to current Object
      */
     public void setNextNode(LinkedList<T> node)
     {
         this.nextNode = node;
     }
 
 
     /**
      *  Returns reference to previous object in list
      *
      * @return  the previous object in the list
      */
     public LinkedList<T> getPrevious()
     {
         return this.prevNode;
     }
 
     /**
      *  Returns reference to next object in list
      *
      * @return  the next object in the list
      */
     public LinkedList<T> getNext()
     {
         return this.nextNode;
     }
 
 }

import java.util.Iterator;

/**
 * Queue Iterator
 *
 * 1. "has a" current reference in Queue
 * 2. supports iterable required methods for next that returns a generic T Object
 */
class QueueIterator<T> implements Iterator<T> {
    LinkedList<T> current;  // current element in iteration

    // QueueIterator is pointed to the head of the list for iteration
    public QueueIterator(LinkedList<T> head) {
        current = head;
    }

    // hasNext informs if next element exists
    public boolean hasNext() {
        return current != null;
    }

    // next returns data object and advances to next position in queue
    public T next() {
        T data = current.getData();
        current = current.getNext();
        return data;
    }
}

/**
 * Queue: custom implementation
 * @author     John Mortensen
 *
 * 1. Uses custom LinkedList of Generic type T
 * 2. Implements Iterable
 * 3. "has a" LinkedList for head and tail
 */
public class Queue<T> implements Iterable<T> {
    LinkedList<T> head = null, tail = null;

    /**
     *  Add a new object at the end of the Queue,
     *
     * @param  data,  is the data to be inserted in the Queue.
     */
    public void add(T data) {
        // add new object to end of Queue
        LinkedList<T> tail = new LinkedList<>(data, null);

        if (this.head == null)  // initial condition
            this.head = this.tail = tail;
        else {  // nodes in queue
            this.tail.setNextNode(tail); // current tail points to new tail
            this.tail = tail;  // update tail
        }
    }

    /**
     *  Returns the data of head.
     *
     * @return  data, the dequeued data
     */
    public T delete() {
        T data = this.peek();
        if (this.tail != null) { // initial condition
            this.head = this.head.getNext(); // current tail points to new tail
            if (this.head != null) {
                this.head.setPrevNode(tail);
            }
        }
        return data;
    }

    /**
     *  Returns the data of head.
     *
     * @return  this.head.getData(), the head data in Queue.
     */
    public T peek() {
        return this.head.getData();
    }

    /**
     *  Returns the head object.
     *
     * @return  this.head, the head object in Queue.
     */
    public LinkedList<T> getHead() {
        return this.head;
    }

    /**
     *  Returns the tail object.
     *
     * @return  this.tail, the last object in Queue
     */
    public LinkedList<T> getTail() {
        return this.tail;
    }

    /**
     *  Returns the iterator object.
     *
     * @return  this, instance of object
     */
    public Iterator<T> iterator() {
        return new QueueIterator<>(this.head);
    }
}

/**
 * Queue Manager
 * 1. "has a" Queue
 * 2. support management of Queue tasks (aka: titling, adding a list, printing)
 */
class QueueManager<T> {
    // queue data
    private final String name; // name of queue
    private int count = 0; // number of objects in queue
    public final Queue<T> queue = new Queue<>(); // queue object

    /**
     *  Queue constructor
     *  Title with empty queue
     */
    public QueueManager(String name) {
        this.name = name;
    }

    /**
     *  Queue constructor
     *  Title with series of Arrays of Objects
     */
    public QueueManager(String name, T[]... seriesOfObjects) {
        this.name = name;
        this.addList(seriesOfObjects);
    }

    /**
     * Add a list of objects to queue
     */
    public void addList(T[]... seriesOfObjects) {  //accepts multiple generic T lists
        for (T[] objects: seriesOfObjects)
            for (T data : objects) {
                this.queue.add(data);
                this.count++;
            }
    }

    /**
     * Print any array objects from queue
     */
    public void printQueue() {
        System.out.println(this.name + " count: " + count);
        System.out.print(this.name + " data: ");
        for (T data : queue)
            System.out.print(data + " ");
        System.out.println();
    }
}

/**
 * Driver Class
 * Tests queue with string, integers, and mixes of Classes and types
 */
class QueueTester {
    public static void main(String[] args)
    {
        // Create iterable Queue of Words
        Object[] words = new String[] { "seven", "slimy", "snakes", "sallying", "slowly", "slithered", "southward"};
        QueueManager qWords = new QueueManager("Words", words );
        qWords.printQueue();

        // Create iterable Queue of Integers
        Object[] numbers = new Integer[] { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9};
        QueueManager qNums = new QueueManager("Integers", numbers );
        qNums.printQueue();

        // Create iterable Queue of NCS Generics
        Animal.setOrder(Animal.KeyType.name);
        Alphabet.setOrder(Alphabet.KeyType.letter);
        Cupcake.setOrder(Cupcake.KeyType.flavor);
        // Illustrates use of a series of repeating arguments
        QueueManager qGenerics = new QueueManager("My Generics",
                Alphabet.alphabetData(),
                Animal.animals(),
                Cupcake.cupcakes()
        );
        qGenerics.printQueue();

        // Create iterable Queue of Mixed types of data
        QueueManager qMix = new QueueManager("Mixed");
        qMix.queue.add("Start");
        qMix.addList(
                words,
                numbers,
                Alphabet.alphabetData(),
                Animal.animals(),
                Cupcake.cupcakes()
        );
        qMix.queue.add("End");
        qMix.printQueue();
    }
}
QueueTester.main(null);