Synchronizing on an object in java, then changing the value of the synchronized-on variable

Question

I came across a code like this

synchronized(obj) {

   obj = new Object();

}

Something does not feel right about this , I am unable to ex

Answer 1

It's a uncommon usage but seems to be of valid in same scenarios. One I found in the codebase of JmDNS:

public Collection getDNSEntryList(String name) {
    Collection entryList = this._getDNSEntryList(name);
    if (entryList != null) {
        synchronized (entryList) {
            entryList = new ArrayList(entryList);
        }
    } else {
        entryList = Collections.emptyList();
    }
    return entryList;
}

What it does is to synchonize on the returned list so this list does not get modified by others and then makes a copy of this list. In this special situation the lock is only needed for the original object.