队列--数组循环队列

 队列一般用循环数组表示。

package dataStructures; public interface Queue { public boolean isEmpty(); public Object getFrontElement(); public Object getRearElement(); public void put(Object theObject); public Object remove(); }

 

/** a queue class that uses a one-dimensional array */ package dataStructures; public class ArrayQueue implements Queue { // data members int front; // one counterclockwise from first element int rear; // position of rear element of queue Object [] queue; // element array // constructors /** create a queue with the given initial capacity */ public ArrayQueue(int initialCapacity) { if (initialCapacity < 1) throw new IllegalArgumentException ("initialCapacity must be >= 1"); queue = new Object [initialCapacity + 1]; // default front = rear = 0 } /** create a queue with initial capacity 10 */ public ArrayQueue() {// use default capacity of 10 this(10); } // methods /** @return true if queue is empty */ public boolean isEmpty() {return front == rear;} /** @return front element of queue * @return null if queue is empty */ public Object getFrontElement() { if (isEmpty()) return null; else return queue[(front + 1) % queue.length]; } /** @return rear element of queue * @return null if the queue is empty */ public Object getRearElement() { if (isEmpty()) return null; else return queue[rear]; } /** insert theElement at the rear of the queue */ public void put(Object theElement) { // increase array length if necessary if ((rear + 1) % queue.length == front) {// double array size // allocate a new array Object [] newQueue = new Object [2 * queue.length]; // copy elements into new array int start = (front + 1) % queue.length; if (start < 2) // no wrap around System.arraycopy(queue, start, newQueue, 0, queue.length - 1); else { // queue wraps around System.arraycopy(queue, start, newQueue, 0, queue.length - start); System.arraycopy(queue, 0, newQueue, queue.length - start, rear + 1); } // switch to newQueue and set front and rear front = newQueue.length - 1; rear = queue.length - 2; // queue size is queue.length - 1 queue = newQueue; } // put theElement at the rear of the queue rear = (rear + 1) % queue.length; queue[rear] = theElement; } /** remove an element from the front of the queue * @return removed element * @return null if the queue is empty */ public Object remove() { if (isEmpty()) return null; front = (front + 1) % queue.length; Object frontElement = queue[front]; queue[front] = null; // enable garbage collection return frontElement; } /** test program */ public static void main(String [] args) { int x; ArrayQueue q = new ArrayQueue(3); // add a few elements q.put(new Integer(1)); q.put(new Integer(2)); q.put(new Integer(3)); q.put(new Integer(4)); // remove and add to test wraparound array doubling q.remove(); q.remove(); q.put(new Integer(5)); q.put(new Integer(6)); q.put(new Integer(7)); q.put(new Integer(8)); q.put(new Integer(9)); q.put(new Integer(10)); q.put(new Integer(11)); q.put(new Integer(12)); // delete all elements while (!q.isEmpty()) { System.out.println("Rear element is " + q.getRearElement()); System.out.println("Front element is " + q.getFrontElement()); System.out.println("Removed the element " + q.remove()); } } }