Question

Hello!

I have a problem in my code please I need help, I don't know How I can wright precondition, so I need help about assertion of pre_condition of peek. Java OOP

Task is!

Improve the circular array implementation of the bounded queue by growing the elements array when the queue is full. Add assertions to check all preconditions of the methods of the bounded queue implementation.

My code is!

public class MessageQueue{

public MessageQueue(int capacity){

elements = new Message[capacity];

count = 0;

head = 0;

tail = 0;

}

/*

   @return the message that has been removed from the queue

   @precondition size() > 0

*/

public Message remove()

{

assert count > 0:"Empty Queue"; //check if elements are there

Message m = elements[head];

head = (head + 1) % elements.length;

count--;

return m;

}

public void add(Message aMessage)

{

if(isFull()){

Message[] new_elements = new Message[count + 1];//Create a new message array by increasing size 1

int i ,j,n;//copy the contents to the new array

for(i=head,j= 0,n=0;n<count; i=(i+1)%elements.length,j++,n++){

new_elements [j] = elements[i];

}

//add the new message at the end of new elements

new_elements [count]= aMessage;

//make elements point to new element

elements = new Message[new_elements.length];

elements = new_elements;

//update the tail,head and count

tail = (count +1)%elements.length;

head=0;

count++;

}

else{

elements[tail] =aMessage;

tail =(tail+1)%elements.length;

count++;

}

}

public int size()

{

return count;

}

public boolean isFull()

{

return count == elements.length;

}

public Message peek()

{

return elements[head];

}

private Message[] elements;

private int head;

private int tail;

private int count;

}

;=================================

public class Message { //greate class message

private String text; //declare of variable

public Message(String text){

this.text=text; //define the variable text

}

//define get text function

public String getText(){

return text;}}

=============================================

public class MessageQueueTest {

public static void main(String[] args) {

MessageQueue tex = new MessageQueue(4);

tex.add(new Message("Hello"));

tex.add(new Message("There !"));

tex.add(new Message("This"));

tex.add(new Message("Massege"));

tex.add(new Message("is :"));

System.out.println("The size is: "+ tex.size());

System.out.println("The head is:"+ tex.peek().getText()+" befor removing");

System.out.println("Remove the head: "+ tex.remove().getText());

tex.add(new Message("greater than the old orginal size"));

while(tex.size()>0)

System.out.println(tex.remove().getText());

}}

==================================

Regardes!

Answer 1

class MessageQueue{

public MessageQueue(int capacity){

elements = new Message[capacity];

count = 0;

head = 0;

tail = 0;

}

/*

@return the message that has been removed from the queue

@precondition size() > 0

*/

public Message remove()

{

assert count > 0:"Empty Queue"; //check if elements are there

Message m = elements[head];

head = (head + 1) % elements.length;

count--;

return m;

}

public void add(Message aMessage)

{

assert count == elements.length:"Queue is full"; //check if elements are there

if(isFull()){

Message[] new_elements = new Message[count + 1];//Create a new message array by increasing size 1

int i ,j,n;//copy the contents to the new array

for(i=head,j= 0,n=0;n<count; i=(i+1)%elements.length,j++,n++){

new_elements [j] = elements[i];

}

//add the new message at the end of new elements

new_elements [count]= aMessage;

//make elements point to new element

elements = new Message[new_elements.length];

elements = new_elements;

//update the tail,head and count

tail = (count +1)%elements.length;

head=0;

count++;

}

else{

elements[tail] =aMessage;

tail =(tail+1)%elements.length;

count++;

}

}

public int size()

{

return count;

}

public boolean isFull()

{

return count == elements.length;

}

public Message peek()

{
assert count == 0:"Empty Queue"; //check if elements are there

return elements[head];

}

private Message[] elements;

private int head;

private int tail;

private int count;

}

//=================================

class Message { //greate class message

private String text; //declare of variable

public Message(String text){

this.text=text; //define the variable text

}

//define get text function

public String getText(){

return text;}}

//=============================================

public class MessageQueueTest {

public static void main(String[] args) {

MessageQueue tex = new MessageQueue(4);

tex.add(new Message("Hello"));

tex.add(new Message("There !"));

tex.add(new Message("This"));

tex.add(new Message("Massege"));

tex.add(new Message("is :"));

System.out.println("The size is: "+ tex.size());

System.out.println("The head is:"+ tex.peek().getText()+" before removing");

System.out.println("Remove the head: "+ tex.remove().getText());

tex.add(new Message("greater than the old orginal size"));

while(tex.size()>0)

System.out.println(tex.remove().getText());
}
}