java lock的tryLock为什么总返回true?

Question

Lock lock = new ReentrantLock();  
lock.lock();

// 此处为何返回true，不应该被锁了吗？
System.out.println(lock.tryLock()); // =>true
 
lock.unlock();
 
System.out.println(lock.tryLock());   // => true

Answer 1

ReentrantLock.tryLock()

Returns:
true if the lock was free and was acquired by the current thread, or the lock was already held by the current thread; andfalse otherwise

ReentrantLock.tryLock() 在当前线程已经持有锁的时候，返回 true。