Queue-linked list queue

Queues represented by linked lists are more efficient in insertion and deletion.

/** Node class used by linked structures. <br/> * this class and its data members are <br/> * visible only within the package datastructures. */</P> <p> package datastructures; </P> <p> class chainnode <br/> {<br/> // package visible data members <br/> object element; <br/> chainnode next; </P> <p> // package visible constructors <br/> chainnode () {}</P> <p> chainnode (object element) <br/> {This. element = element ;}</P> <p> chainnode (object element, chainnode next) <br/> {This. element = element; <br/> This. next = next ;}< br/>}< br/>

 

/** A linked queue class */</P> <p> package datastructures; </P> <p> public class incluqueue implements queue <br/> {<br/> // data members <br/> protected chainnode front; <br/> protected chainnode rear; </P> <p> // constructors <br/>/** create an empty queue */<br/> Public incluqueue (INT initialcapacity) <br/>{< br/> // The default initial value of front is null <br/>}</P> <p> Public writable Queue () <B R/> {This (0 );} </P> <p> // methods <br/>/** @ return true iff queue is empty */<br/> Public Boolean isempty () <br/> {return front = NULL ;} </P> <p>/** @ return the element at the front of the queue <br/> * @ return NULL if the queue is empty */<br/> Public object getfrontelement () <br/>{< br/> If (isempty () <br/> return NULL; <br/> else <br/> return front. element; <br/>}</P> <p>/** @ return the E LEMENT at the rear of the queue <br/> * @ return NULL if the queue is empty */<br/> Public object getrearelement () <br/>{< br/> If (isempty () <br/> return NULL; <br/> else <br/> return rear. element; <br/>}</P> <p>/** insert theelement at the rear of the queue */<br/> Public void put (Object theelement) <br/>{< br/> // create a node for theelement <br/> chainnode P = new chainnode (theelement, n Ull); </P> <p> // append P to the chain <br/> If (front = NULL) <br/> front = P; // empty queue <br/> else <br/> rear. next = P; // nonempty queue <br/> rear = P; <br/>}</P> <p>/** remove an element from the front of the queue <br/> * @ return removed element <br/> * @ return null if the queue is empty */<br/> Public object remove () <br/>{< br/> If (isempty () <br/> return NULL; <br/> Object fronte LEMENT = front. element; <br/> front = front. next; <br/> If (isempty () <br/> rear = NULL; // enable garbage collection <br/> return frontelement; <br/>}</P> <p>/** Test Program */<br/> Public static void main (string [] ARGs) <br/>{< br/> int X; <br/> queue q = new queue Queue (3 ); <br/> // Add a few elements <br/> q. put (New INTEGER (1); <br/> q. put (New INTEGER (2); <br/> q. put (New INTEGER (3); <br/> q. Put (New INTEGER (4); </P> <p> // delete all elements <br/> while (! Q. isempty () <br/>{< br/> system. out. println ("rear element is" + q. getrearelement (); <br/> system. out. println ("front element is" + q. getfrontelement (); <br/> system. out. println ("removed the element" + q. remove (); <br/>}< br/>