在Java中，`synchronized`等同于`synchronized（this）`？(In Java, is `synchronized` equivalent to `synchronized (this)`?)

 我正在查看DatagramSocket的源代码，我发现了这个： 
 
public void disconnect() {
    synchronized (this) {
        if (isClosed())
            return;
        if (connectState == ST_CONNECTED) {
            impl.disconnect ();
        }
        connectedAddress = null;
        connectedPort = -1;
        connectState = ST_NOT_CONNECTED;
    }
}
 
 我对同步方法的理解是他们锁定了this 。 那么代码是否等同于以下内容？ 
 
public synchronized void disconnect() {
    if (isClosed())
        return;
    if (connectState == ST_CONNECTED) {
        impl.disconnect ();
    }
    connectedAddress = null;
    connectedPort = -1;
    connectState = ST_NOT_CONNECTED;
}
 
 语言设计者选择不在此使用同步方法是否有原因？ 

I was looking through the source code for DatagramSocket and I found this: 
 
public void disconnect() {
    synchronized (this) {
        if (isClosed())
            return;
        if (connectState == ST_CONNECTED) {
            impl.disconnect ();
        }
        connectedAddress = null;
        connectedPort = -1;
        connectState = ST_NOT_CONNECTED;
    }
}
 
My understanding of synchronized methods is that they lock on this. So is the code equivalent to the following? 
 
public synchronized void disconnect() {
    if (isClosed())
        return;
    if (connectState == ST_CONNECTED) {
        impl.disconnect ();
    }
    connectedAddress = null;
    connectedPort = -1;
    connectState = ST_NOT_CONNECTED;
}
 
Is there a reason why the language designers chose not to use a synchronized method here?

原文：https://stackoverflow.com/questions/32474815