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package DataStructures.Queues;

import java.util.ArrayList;

/**

* This class implements a GenericArrayListQueue.

* <p>

* A GenericArrayListQueue data structure functions the same as any specific-typed queue.

* The GenericArrayListQueue holds elemets of types to-be-specified at runtime.

* The elements that are added first are the first to be removed (FIFO)

* New elements are added to the back/rear of the queue.

*

*/

public class GenericArrayListQueue<T> {

/**

* The generic ArrayList for the queue

* T is the generic element

*/

ArrayList<T> _queue = new ArrayList<T>();

/**

* Checks if the queue has elements (not empty)

*

* @return True if the queue has elements. False otherwise.

*/

private boolean hasElements() {

return !_queue.isEmpty();

}

/**

* Checks what's at the front of the queue

*

* @return If queue is not empty, element at the front of the queue. Otherwise, null

*/

public T peek() {

T result = null;

if(this.hasElements()) { result = _queue.get(0); }

return result;

}

/**

* Inserts an element of type T to the queue.

*

* @param element of type T to be added

* @return True if the element was added successfully

*/

public boolean add(T element) {

return _queue.add(element);

}

/**

* Retrieve what's at the front of the queue

*

* @return If queue is not empty, element retrieved. Otherwise, null

*/

public T poll() {

T result = null;

if(this.hasElements()) { result = _queue.remove(0); }

return result;

}

/**

* Main method

*

* @param args Command line arguments

*/

public static void main(String[] args) {

GenericArrayListQueue<Integer> queue = new GenericArrayListQueue<Integer>();

System.out.println("Running...");

assert queue.peek() == null;

assert queue.poll() == null;

assert queue.add(1) == true;

assert queue.peek() == 1;

assert queue.add(2) == true;

assert queue.peek() == 1;

assert queue.poll() == 1;

assert queue.peek() == 2;

assert queue.poll() == 2;

assert queue.peek() == null;

assert queue.poll() == null;

System.out.println("Finished.");

}

}