In Java, when you define a new exception by extending an existing exception class, it's called "Customization of exception." This process allows you to create your own exception classes that suit your application's specific needs while maintaining compatibility with Java's exception hierarchy.

To read data from an InputStream object connected to a socket, you typically use the read() method. This method reads a single byte of data and returns an integer representation of that byte. You can then cast it to the appropriate data type. The other options are not standard methods for reading from sockets.

To ensure that a particular section of code does not have concurrent access by multiple threads, you can use the ReentrantLock class from the java.util.concurrent package. This allows you to create a lock that multiple threads can use to synchronize access to a critical section of code. Unlike synchronized methods, it provides more fine-grained control over locking.

In Java, the wait() method is used for inter-thread communication and is typically used with synchronization mechanisms like synchronized blocks. It releases the lock and allows other threads to execute, whereas sleep() pauses the thread but retains the lock, making it unsuitable for inter-thread communication.

In Java, the ! (logical NOT) operator is used to invert or negate the value of a boolean expression. It changes true to false and vice versa, making it a fundamental operator for boolean logic in Java.

The InputStream and OutputStream classes are part of the java.io package in Java. These classes are used for reading and writing data in a byte-oriented manner, making them essential for I/O operations.

When a thread tries to access a synchronized block in Java, it must first obtain the "Lock" on the object. This ensures that only one thread can execute the synchronized code block at a time, preventing race conditions.

The correct answer is getPort(). In Java, the URL class provides the getPort() method, which allows you to obtain the port number of a URL. This is useful when working with network-related tasks where you need to know the port associated with a particular URL.

In Java, the commonly used class for reading characters from a file is FileReader. It is part of the java.io package and is specifically designed for character input. Other options like FileWriter, FileInputReader, and FileOutputReader are not standard classes in Java for file reading.

The executeQuery() method in JDBC is used to execute SQL queries that return a ResultSet, typically used for SELECT statements. The executeUpdate() method is used for executing SQL queries that modify the database, such as INSERT, UPDATE, or DELETE statements. The other options mentioned are not valid JDBC methods.