public class ArrayBlockingQueue<E> extends AbstractQueue<E> implements BlockingQueue<E>, java.io.Serializable {
/** 隊列元素 數組 */
private final E[] items;
/** 獲取、刪除元素時的索引（take, poll 或 remove操作） */
private int takeIndex;
/** 添加元素時的索引（put, offer或 add操作） */
private int putIndex;
/** 隊列元素的數目*/
private int count;
/** 鎖 */
private final ReentrantLock lock;
/** 獲取操作時的條件 */
private final Condition notEmpty;
/** 插入操作時的條件 */
private final Condition notFull;
//超出數組長度時，重設為0
final int inc(int i) {
return (++i == items.length)? 0 : i;
}
/**
* 插入元素（在獲得鎖的情況下才調用）
*/
private void insert(E x) {
items[putIndex] = x;
putIndex = inc(putIndex);
++count;
notEmpty.signal();
}
/**
* 獲取并移除元素（在獲得鎖的情況下才調用）
*/
private E extract() {
final E[] items = this.items;
E x = items[takeIndex];
items[takeIndex] = null;
takeIndex = inc(takeIndex);//移到下一個位置
--count;
notFull.signal();
return x;
}
/**
* 刪除i位置的元素
*/
void removeAt(int i) {
final E[] items = this.items;
// if removing front item, just advance
if (i == takeIndex) {
items[takeIndex] = null;
takeIndex = inc(takeIndex);
} else {
// 把i后面的直到putIndex的元素都向前移動一個位置
for (;;) {
int nexti = inc(i);
if (nexti != putIndex) {
items[i] = items[nexti];
i = nexti;
} else {
items[i] = null;
putIndex = i;
break;
}
}
}
--count;
notFull.signal();
}
/**
*構造方法，指定容量，默認策略（不是按照FIFO的順序訪問）
*/
public ArrayBlockingQueue(int capacity) {
this(capacity, false);
}
/**
*構造方法，指定容量及策略
*/
public ArrayBlockingQueue(int capacity, boolean fair) {
if (capacity <= 0)
throw new IllegalArgumentException();
this.items = (E[]) new Object[capacity];
lock = new ReentrantLock(fair);
notEmpty = lock.newCondition();
notFull = lock.newCondition();
}
/**
* 通過集合構造
*/
public ArrayBlockingQueue(int capacity, boolean fair,
Collection<? extends E> c) {
this(capacity, fair);
if (capacity < c.size())
throw new IllegalArgumentException();
for (Iterator<? extends E> it = c.iterator(); it.hasNext();)
add(it.next());
}
/**
* 插入元素到隊尾（super調用offer方法）
* public boolean add(E e) {
* if (offer(e))
* return true;
* else
* throw new IllegalStateException("Queue full");
* }
* 將指定的元素插入到此隊列的尾部（如果立即可行且不會超過該隊列的容量），
* 在成功時返回 true，如果此隊列已滿，則拋出 IllegalStateException。
*/
public boolean add(E e) {
return super.add(e);
}
/**
* 將指定的元素插入到此隊列的尾部（如果立即可行且不會超過該隊列的容量），
* 在成功時返回 true，如果此隊列已滿，則返回 false。
*/
public boolean offer(E e) {
if (e == null) throw new NullPointerException();
final ReentrantLock lock = this.lock;
lock.lock();
try {
if (count == items.length)
return false;
else {
insert(e);
return true;
}
} finally {
lock.unlock();
}
}
/**
* 將指定的元素插入此隊列的尾部，如果該隊列已滿，則等待可用的空間。
*/
public void put(E e) throws InterruptedException {
if (e == null) throw new NullPointerException();
final E[] items = this.items;
final ReentrantLock lock = this.lock;
lock.lockInterruptibly();
try {
try {
while (count == items.length)
notFull.await();
} catch (InterruptedException ie) {
notFull.signal(); // propagate to non-interrupted thread
throw ie;
}
insert(e);
} finally {
lock.unlock();
}
}
/**
* 將指定的元素插入此隊列的尾部，如果該隊列已滿，則在到達指定的等待時間之前等待可用的空間。
*/
public boolean offer(E e, long timeout, TimeUnit unit)
throws InterruptedException {
if (e == null) throw new NullPointerException();
long nanos = unit.toNanos(timeout);
final ReentrantLock lock = this.lock;
lock.lockInterruptibly();
try {
for (;;) {
if (count != items.length) {
insert(e);
return true;
}
if (nanos <= 0)//如果時間到了就返回
return false;
try {
nanos = notFull.awaitNanos(nanos);
} catch (InterruptedException ie) {
notFull.signal(); // propagate to non-interrupted thread
throw ie;
}
}
} finally {
lock.unlock();
}
}
//獲取并移除此隊列的頭，如果此隊列為空，則返回 null。
public E poll() {
final ReentrantLock lock = this.lock;
lock.lock();
try {
if (count == 0)
return null;
E x = extract();
return x;
} finally {
lock.unlock();
}
}
//獲取并移除此隊列的頭部，在元素變得可用之前一直等待（如果有必要）。
public E take() throws InterruptedException {
final ReentrantLock lock = this.lock;
lock.lockInterruptibly();
try {
try {
while (count == 0)
notEmpty.await();
} catch (InterruptedException ie) {
notEmpty.signal(); // propagate to non-interrupted thread
throw ie;
}
E x = extract();
return x;
} finally {
lock.unlock();
}
}
//獲取并移除此隊列的頭部，在指定的等待時間前等待可用的元素（如果有必要）。
public E poll(long timeout, TimeUnit unit) throws InterruptedException {
long nanos = unit.toNanos(timeout);
final ReentrantLock lock = this.lock;
lock.lockInterruptibly();
try {
for (;;) {
if (count != 0) {
E x = extract();
return x;
}
if (nanos <= 0)
return null;
try {
nanos = notEmpty.awaitNanos(nanos);
} catch (InterruptedException ie) {
notEmpty.signal(); // propagate to non-interrupted thread
throw ie;
}
}
} finally {
lock.unlock();
}
}
//獲取但不移除此隊列的頭；如果此隊列為空，則返回 null。
public E peek() {
final ReentrantLock lock = this.lock;
lock.lock();
try {
return (count == 0) ? null : items[takeIndex];
} finally {
lock.unlock();
}
}
/**
* 返回此隊列中元素的數量。
*/
public int size() {
final ReentrantLock lock = this.lock;
lock.lock();
try {
return count;
} finally {
lock.unlock();
}
}
/**
*返回在無阻塞的理想情況下（不存在內存或資源約束）此隊列能接受的其他元素數量。
*/
public int remainingCapacity() {
final ReentrantLock lock = this.lock;
lock.lock();
try {
return items.length - count;
} finally {
lock.unlock();
}
}
/**
* 從此隊列中移除指定元素的單個實例（如果存在）。
*/
public boolean remove(Object o) {
if (o == null) return false;
final E[] items = this.items;
final ReentrantLock lock = this.lock;
lock.lock();
try {
int i = takeIndex;
int k = 0;
for (;;) {
if (k++ >= count)
return false;
if (o.equals(items[i])) {
removeAt(i);
return true;
}
i = inc(i);
}
} finally {
lock.unlock();
}
}
/**
* 如果此隊列包含指定的元素，則返回 true。
*/
public boolean contains(Object o) {
if (o == null) return false;
final E[] items = this.items;
final ReentrantLock lock = this.lock;
lock.lock();
try {
int i = takeIndex;
int k = 0;
while (k++ < count) {
if (o.equals(items[i]))
return true;
i = inc(i);
}
return false;
} finally {
lock.unlock();
}
}
……
}