Synchronized statements and separate unsynchronized methods

Question

On the Java documentation online I found the following example:

public void addName(String name) {
    synchronized(this) {
        lastName = name;
        nameCount++;
    }
    nameList.add(name);
}

They state:

Without synchronized statements, there would have to be a separate, unsynchronized method for the sole purpose of invoking nameList.add.

Does someone understand what they mean?

The source can be found here.

Answer 1

The article first introduces synchronized methods - so up to this point, the reader may believe that the unit of granularity of synchronization is a single method.

And indeed, if synchronized blocks/statements didn't exist, the example above could only be accomplished as:

public void addName(String name) {
    doSyncAdd(name);
    nameList.add(name);
}

private synchronized void doSyncAdd(String name) {
    lastName = name;
    nameCount++;
}

So, synchronized statements mean you can keep related code that needs to be synchronized inline. Rather than having to declare a separate method, which both pollutes the namespace and fragments the flow of the code. (Well, factoring out methods is good in moderation but it's nicer to have the choice.)

Answer 2

It means that your code snippet can be rewritten as

public void addName(String name) {
    setName(name)
    nameList.add(name);
}

private synchronized void setName(String name) {
    lastName = name;
    nameCount++;
}

i.e. as synchronized(this) is the same as a synchronized instance (non-static) method the code in the synchronized block can be moved to a synchronized method and called from the unsynchronized method. The effect will be the same.