jdk1.5并发包中ReentrantLock的创建可以指定构造函数的boolean类型来得到公平锁或非公平锁，关于两者区别，java并发编程实践里面有解释

公平锁： Threads acquire a fair lock in the order in which they requested it
非公平锁：a nonfair lock permits barging: threads requesting a lock can jump ahead of the queue
of waiting threads if the lock happens to be available when it is requested.

公平锁，就是很公平，在并发环境中，每个线程在获取锁时会先查看此锁维护的等待队列，如果为空，或者当前线程线程是等待队列的第一个，就占有锁，否则就会加入到等待队列中，以后会按照FIFO的规则从队列中取到自己

非公平锁比较粗鲁，上来就直接尝试占有锁，如果尝试失败，就再采用类似公平锁那种方式

//公平获取锁 java.util.concurrent.locks.ReentrantLock$FairSync.java


}

//非公平获取锁 java.util.concurrent.locks.ReentrantLock$UnFairSync.java

final boolean nonfairTryAcquire(int acquires) {
final Thread current = Thread.currentThread();
int c = getState();
if (c == 0) {

//如果当前没有线程占有锁，当前线程直接通过cas指令占有锁，管他等待队列，就算自己排在队尾也是这样
if (compareAndSetState(0, acquires)) {
setExclusiveOwnerThread(current);
return true;
}
}
else if (current == getExclusiveOwnerThread()) {
int nextc = c + acquires;
if (nextc < 0) // overflow
throw new Error("Maximum lock count exceeded");
setState(nextc);
return true;
}
return false;
}