/** * Book: Data Structures and Algorithms in Java, by Robert LaFore * Chapter 4: * queue.java * demonstrates queue * to compile this code: javac queue.java * to run this program: java QueueApp */ class Queue { private int maxSize; private long[] queArray; private int front; private int rear; private int nItems; public Queue(int s) { // constructor maxSize = s; queArray = new long[maxSize]; front = 0; rear = -1; nItems = 0; } public void insert(long j) { // put item at rear of queue if (rear == maxSize-1) // deal with wraparound rear = -1; queArray[++rear] = j; // increment rear and insert nItems++; // one more item } public long remove() { // take item from front of queue long temp = queArray[front++]; // get value and incr front if (front == maxSize) // deal with wraparound front = 0; nItems--; // one less item return temp; } public long peekFront() { // peek at front of queue return queArray[front]; } public boolean isEmpty() { // true if queue is empty return (nItems==0); } public boolean isFull() { // true if queue is full return (nItems==maxSize); } public int size() { // number of items in queue return nItems; } } // end class Queue class QueueApp { public static void main(String[] args) { Queue theQueue = new Queue(5); // queue holds 5 items theQueue.insert(10); // insert 4 items theQueue.insert(20); theQueue.insert(30); theQueue.insert(40); theQueue.remove(); // remove 3 items theQueue.remove(); // (10, 20, 30) theQueue.remove(); theQueue.insert(50); // insert 4 more items theQueue.insert(60); // (wraps around) theQueue.insert(70); theQueue.insert(80); while (!theQueue.isEmpty()) { // remove and display all items long n = theQueue.remove(); // (40, 50, 60, 70, 80) System.out.print(n + " "); } System.out.println(""); } }