class ConnectionPoolManager {
private static final Object LOCK = new Object();
private static ConnectionPoolManager connectionPoolManager = null;
public static ConnectionPoolManager getInstance() {
//这里有两次判断,我理解为减少不必要的同步开销
if (connectionPoolManager == null) {
synchronized (LOCK) {
if (connectionPoolManager == null) {
connectionPoolManager = new ConnectionPoolManager();
}
}
}
return connectionPoolManager;
}
private ConnectionPoolManager(){
super();
}
}
感谢一下下面这个哥们的提醒。