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package horstmann.ch03_queue;
/**
A first-in, first-out bounded collection of messages.
*/
public class MessageQueue
{
/**
Constructs an empty message queue.
@param capacity the maximum capacity of the queue
<p><b>Precondition:</b> capacity > 0
*/
public MessageQueue(int capacity)
{
elements = new Message[capacity];
count = 0;
head = 0;
tail = 0;
}
/**
Remove message at head.
@return the message that has been removed from the queue
<p><b>Precondition:</b> size() > 0
*/
public Message remove()
{
Message r = elements[head];
head = (head + 1) % elements.length;
count--;
return r;
}
/**
Append a message at tail.
@param aMessage the message to be appended
<p><b>Precondition:</b> !isFull();
*/
public void add(Message aMessage)
{
elements[tail] = aMessage;
tail = (tail + 1) % elements.length;
count++;
}
/**
Get the total number of messages in the queue.
@return the total number of messages in the queue
*/
public int size()
{
return count;
}
/**
Checks whether this queue is full
@return true if the queue is full
*/
public boolean isFull()
{
return count == elements.length;
}
/**
Get message at head.
@return the message that is at the head of the queue
<p><b>Precondition:</b> size() > 0
*/
public Message peek()
{
return elements[head];
}
private Message[] elements;
private int head;
private int tail;
private int count;
}
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