The JCF class Deque had a method called contains that would return true if an Ob
ID: 3730592 • Letter: T
Question
The JCF class Deque had a method called contains that would return true if an Object was in the deque. For a que, the method could be specified as follows:
public boolean contains(Object o)
//Returns true if this queue contains the specified element.
a. Add this method to the QueueListBased implementation gien in this chapter.
public class QueueListBased implements QueueInterface{
private ListInterface aList;
public QueueListBased(){
aList=new ListReferenceBased();
}
public boolean isEmpty(){
return aList.isEmpty();
}
public void enqueue(Object newItem){
aList.add(aList.size(),newItem);
}
public Object dequeue() throws QueueException{
if(!isEmptry()){
Object queueFront=aList.get(0);
aList.remove(0);
return queueFront;
}else{
throw new QueueException("Queue exception on dequeue: "+ " queue empty");
}
}
public void dequeueAll(){
aList.removeAll();
}
public Object peek() throws QueueException{
if(!isEmptry()){
return aList.get(0);
}else{
throw new QueueException("Queue exception on peek " +" queue emptry");
}
}
}
b. Add this method to the QueueArrayBased implementation given in this chapter.
public class queueArrayBased implements QueueInterface{
private final int MAX_QUEUE=50;
private Object[] items;
private int front, back, count;
public QueueArrayBased(){
items = new Object[MAX_QUEUE];
front=0;
back=MAX_QUEUE-1;
count=0;
}
public boolean isEmptry(){
return count ==0;
}
public boolean isFull(){
return count ==MAX_QUEUE;
}
public void enqueue(Object newItem) throws QueueException{
if(!isFull()){
back=(back+1) %(MAX_QUEUE);
items[back]=newItem;
++count;
}else{
throw new QueueException("QueueException on enqueue: " + "Queue full");
}
}
public Object dequeue() throws QueueException{
if(!isEmptry()){
Object queueFront =items[front];
front=(front+1)%(MAX_QUEUE);
--count;
return queuFront;
}else{
throw new QueueException("QueueExcetion on dequeue: " + "Queue empty");
}
}
public void dequeueAll(){
items=new Object[MAX_QUEUE];
front =0;
back=MAX_QUEUE-1;
count=0;
}
public Object peek() throws QueueException{
if(!isEmptry()){
return items[front];
}else{
thrownew QueueException("Queue exception on peek: "+"Queue empty");
}
}
}
c. Add this method to the QueueReferenceBased implementation given in this chapter.
public class QueueReferenceBased implements QueueInterface{
private Noce lastNode;
public QueueReferenceBased(){
lastNode=null;
}
public boolean isEmpty(){
return lastNode==null;
}
public void dequeAll(){
lastNode=null;
}
public void enqueue(Object newItem){
Node newNode=new Node(newItem);
if(!isEmpty)){
newNode.next=newNode;
}else{
newNode.next=lastNode.next;
lastNode.next=newNode;
}
lastNode=newNode;
}
public Object dequeue() throws QueueException{
if(!isEmpty()){
Node firstNode=lastNode.next;
if(firstNode==lastNode){
lastNode=null;
}else{
lastNode.next=firstNode.next;
}
return firstNode.item;
}else{
throw new QueueExceptioin("QueueException on dequeue:" +"queue empty");
}
}
public Object peek() throws QueueException{
if(!isEmpty)){
Node firstNode = astNode.next;
return firstNode.item;
}else{
throw new QueueException("QueueException on peek:" +queue empty");
}
}
}
Explanation / Answer
a)
public class QueueListBased implements QueueInterface{
private ListInterface aList;
public QueueListBased(){
aList=new ListReferenceBased();
}
public boolean isEmpty(){
return aList.isEmpty();
}
public void enqueue(Object newItem){
aList.add(aList.size(),newItem);
}
public Object dequeue() throws QueueException{
if(!isEmptry()){
Object queueFront=aList.get(0);
aList.remove(0);
return queueFront;
}else{
throw new QueueException("Queue exception on dequeue: "+ " queue empty");
}
}
public void dequeueAll(){
aList.removeAll();
}
public Object peek() throws QueueException{
if(!isEmptry()){
return aList.get(0);
}else{
throw new QueueException("Queue exception on peek " +" queue emptry");
}
}
public boolean contains(Object o){
if(o==null){
return false;
}
int i=0;
while(i<aList.size()){
if(o.equals(aList.get(i))){
return true;
}
i++;
}
return false;
}
}
b)
public class queueArrayBased implements QueueInterface{
private final int MAX_QUEUE=50;
private Object[] items;
private int front, back, count;
public QueueArrayBased(){
items = new Object[MAX_QUEUE];
front=0;
back=MAX_QUEUE-1;
count=0;
}
public boolean isEmptry(){
return count ==0;
}
public boolean isFull(){
return count ==MAX_QUEUE;
}
public void enqueue(Object newItem) throws QueueException{
if(!isFull()){
back=(back+1) %(MAX_QUEUE);
items[back]=newItem;
++count;
}else{
throw new QueueException("QueueException on enqueue: " + "Queue full");
}
}
public Object dequeue() throws QueueException{
if(!isEmptry()){
Object queueFront =items[front];
front=(front+1)%(MAX_QUEUE);
--count;
return queuFront;
}else{
throw new QueueException("QueueExcetion on dequeue: " + "Queue empty");
}
}
public void dequeueAll(){
items=new Object[MAX_QUEUE];
front =0;
back=MAX_QUEUE-1;
count=0;
}
public Object peek() throws QueueException{
if(!isEmptry()){
return items[front];
}else{
thrownew QueueException("Queue exception on peek: "+"Queue empty");
}
}
public boolean contains(Object o){
if(o==null){
return false;
}
int i=front;
while(i<back){
if(o.equals(items[i])){
return true;
}
i++;
}
return false;
}
}
c)
public class QueueReferenceBased implements QueueInterface{
private Noce lastNode;
public QueueReferenceBased(){
lastNode=null;
}
public boolean isEmpty(){
return lastNode==null;
}
public void dequeAll(){
lastNode=null;
}
public void enqueue(Object newItem){
Node newNode=new Node(newItem);
if(!isEmpty)){
newNode.next=newNode;
}else{
newNode.next=lastNode.next;
lastNode.next=newNode;
}
lastNode=newNode;
}
public Object dequeue() throws QueueException{
if(!isEmpty()){
Node firstNode=lastNode.next;
if(firstNode==lastNode){
lastNode=null;
}else{
lastNode.next=firstNode.next;
}
return firstNode.item;
}else{
throw new QueueExceptioin("QueueException on dequeue:" +"queue empty");
}
}
public Object peek() throws QueueException{
if(!isEmpty)){
Node firstNode = astNode.next;
return firstNode.item;
}else{
throw new QueueException("QueueException on peek:" +queue empty");
}
}
public boolean contains(Object o){
if(o==null){
return false;
}
Node itr=firstNode;
while(itr!=lastNode){
if(o.equals(itr.item)){
return true;
}
itr=itr.next;
}
return false;
}
}
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