可以在方法级别同步被Lock代替吗？

Question

When writing a thread safe class, we use synchronized keyword at two places in code,

1.Method level synchronization

2.Synchronized blocks

As far as I can think of, interfaces like Lock ( java.util.concurrent.locks.Lock )can be used in place of synchronized only at block level but not at method level. or is there a way?

I don't have any real need of it but just curios since heard discussions that Lock can be a replacement for synchronized .

public class SampleClass {
    public synchronized void method(){
      .....
    }
}

Answer 1

There is no special syntax for "acquire the Lock at the beginning of the method, and release it at the end," like there is for synchronized .

You can, of course, just do that yourself:

public void method() {
    lock.lock();
    try {
        // rest of the method
    } finally {
        lock.unlock();
    }
}

Answer 2

As we all know

public class SampleClass {
    public synchronized void method(){
      .....
    }
}

and

public class SampleClass {
    public void method(){
        synchronized(this) {
           .....
        }
    }
}

is equivalent for all practical purposes.

So you need to change method synchronization to equivalent block synchronization and the later can be replaced by Lock

Answer 3

No, there's no way to do this since java.util.concurrent —and therefore Lock or any other implementation as well—is just a library, whereas synchronized is part of the Java Language Specification .

Regarding " Lock can be a replacement for synchronized", Brian Goetz discusses this in "Java Concurrency in Practice" in chapter 13.4:

ReentrantLock is an advanced tool for situations where intrinsic locking is not practical. Use it if you need its advanced features: timed, polled, or interruptible lock acquisition, fair queueing, or non-block-structured locking. Otherwise, prefer synchronized.