arrayqueue.java

JAVA 所有包

/*
 * @(#)ArrayQueue.java	1.7 05/11/17
 * 
 * Copyright 2006 Sun Microsystems, Inc. All rights reserved.
 * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 */

package com.sun.jmx.remote.internal;

import java.util.AbstractList;
import java.util.Iterator;

public class ArrayQueue<T> extends AbstractList<T> {
    public ArrayQueue(int capacity) {
	this.capacity = capacity + 1;
	this.queue = (T[]) new Object[capacity + 1];
	this.head = 0;
	this.tail = 0;
    }

    public void resize(int newcapacity) {
	int size = size();
	if (newcapacity < size)
	    throw new IndexOutOfBoundsException("Resizing would lose data");
	newcapacity++;
	if (newcapacity == this.capacity)
	    return;
	T[] newqueue = (T[]) new Object[newcapacity];
	for (int i = 0; i < size; i++)
	    newqueue[i] = get(i);
	this.capacity = newcapacity;
	this.queue = newqueue;
	this.head = 0;
	this.tail = size;
    }

    public boolean add(T o) {
	queue[tail] = o;
	int newtail = (tail + 1) % capacity;
	if (newtail == head)
	    throw new IndexOutOfBoundsException("Queue full");
	tail = newtail;
	return true; // we did add something
    }

    public T remove(int i) {
	if (i != 0)
	    throw new IllegalArgumentException("Can only remove head of queue");
	if (head == tail)
	    throw new IndexOutOfBoundsException("Queue empty");
	T removed = queue[head];
	queue[head] = null;
	head = (head + 1) % capacity;
	return removed;
    }

    public T get(int i) {
	int size = size();
	if (i < 0 || i >= size) {
	    final String msg = "Index " + i + ", queue size " + size;
	    throw new IndexOutOfBoundsException(msg);
	}
	int index = (head + i) % capacity;
	return queue[index];
    }

    public int size() {
	// Can't use % here because it's not mod: -3 % 2 is -1, not +1.
	int diff = tail - head;
	if (diff < 0)
	    diff += capacity;
	return diff;
    }

    private int capacity;
    private T[] queue;
    private int head;
    private int tail;
}