20162316刘诚昊 用数组实现循环队列

20162316刘诚昊 2017-2018-2 《Java程序设计》用数组实现循环队列

实验要求

过程

import Week_5.EmptyCollectionException;

public class CircularArrayQueue<T> implements QueueADT<T>
{
private final int DEFAULT_CAPACITY = 10;
private int front, rear, count;
private T[] queue;

/*
* Creates an empty queue using the default capacity.
*/
public CircularArrayQueue()
{
front = rear = count = 0;
queue = (T[]) (new Object[DEFAULT_CAPACITY]);
}

/**

* Adds the specified element to the rear of this queue, expanding

* the capacity of the queue array if necessary.

*/
public void enqueue (T element)
{
if (size() == queue.length)
expandCapacity();

queue[rear] = element;
rear = (rear+1) % queue.length;

count++;
}

/**
* Removes the element at the front of this queue and returns a
* reference to it. Throws an EmptyCollectionException if the
* queue is empty.
*/
public T dequeue() throws EmptyCollectionException
{
if (isEmpty())
throw new EmptyCollectionException ("queue");

T result = queue[front];
queue[front] = null;
front = (front+1) % queue.length;

count--;

return result;
}

/*
* Returns a reference to the element at the front of this queue.
* The element is not removed from the queue.  Throws an
* EmptyCollectionException if the queue is empty.
*/
public T first() throws EmptyCollectionException
{
if (isEmpty())
throw new EmptyCollectionException ("queue");

return queue[front];
}

public boolean isEmpty()
{
return (count == 0);
}

public int size()
{
return count;
}

public String toString()
{
String result = "";

for(int num = 0; num<count; num++){
result = result + queue[(front+num)%queue.length] + " ";
}

return result;
}

/**

* Creates a new array to store the contents of this queue with

* twice the capacity of the old one.

*/
public void expandCapacity()
{
T[] larger = (T[])(new Object[queue.length *2]);

for(int scan=0; scan < count; scan++)
{
larger[scan] = queue[front];
front=(front+1) % queue.length;
}

front = 0;
rear = count;
queue = larger;
}
}

public class CircularArrayQueueTest extends TestCase {
CircularArrayQueue CAQ = new CircularArrayQueue();
public void testDequeue() throws Exception {
CAQ.enqueue(01);
CAQ.enqueue(02);
assertEquals(01,CAQ.dequeue());
assertEquals(02,CAQ.dequeue());
}

public void testFirst() throws Exception {
CAQ.enqueue(01);
CAQ.enqueue(02);
assertEquals(01,CAQ.first());
}

public void testIsEmpty() throws Exception {
assertEquals(true,CAQ.isEmpty());
CAQ.enqueue(01);
assertEquals(false,CAQ.isEmpty());
}

public void testSize() throws Exception {
CAQ.enqueue(01);
CAQ.enqueue(02);
CAQ.enqueue(03);
CAQ.enqueue(04);
assertEquals(4,CAQ.size());
}

public void testToString() throws Exception {
CAQ.enqueue(01);
CAQ.enqueue(02);
CAQ.enqueue(03);
CAQ.enqueue(04);
assertEquals(1+ " " + 2+" " +3+" " +4 + " ",CAQ.toString()
);
}

}