使用ReentrantLock可靠吗？

Question

I searched a lot but was confused with the process of 'ReentrantLock' and normal 'synchronized' .

For example( 1 ):

Object obj = new Object();

synchronized(obj){
//lock is guaranteed to be acquired 
}

example( 2 )

Lock lock = new ReentrantLock();
lock.lock(); //problem here
try{
//dostuff
}
finally{
lock.unlock();
}

My question is:

In example 1 : it is guaranteed to acquire a lock on the object using the synchronized keyword.

But

In example 2 : is it guaranteed that the lock will be acquired using the lock.lock() method?? or will the thread proceed to the next line for the execution?? without acquiring the lock.

I doubt it because, using threads had resulted in unexpected outcomes for me many times.

Answer 1

Only one thread will acquire the lock: this is the contract of ReentrantLock .

Therefore your example 2 is perfectly thread safe.