Using SocketChannel in non-blocking mode (option a) can lead to improved performance with lower CPU usage compared to traditional blocking I/O sockets. Non-blocking SocketChannels can handle multiple connections concurrently. Option c is incorrect because non-blocking SocketChannels are often favored for high-throughput scenarios. Option d is not accurate as data integrity is not directly related to blocking or non-blocking mode.

In Java, the shutdown() method of ExecutorService attempts to stop all actively executing tasks and halts the processing of waiting tasks. It's a graceful way to shut down an executor, allowing it to finish executing tasks before terminating. It is essential to manage thread pools effectively in concurrent applications.

The intern() method of the String class is used to add the String to the string pool if it's not already there and returns a reference to that String. This can reduce memory usage by ensuring only one copy of a particular string exists in the string pool, which is useful for memory optimization. The intern() method has been available since early versions of Java, not just in Java 9 and later.

In a single-threaded application with frequent string concatenation, StringBuilder is the most suitable choice. It's efficient because it doesn't create new objects when you modify the string, which can save memory and reduce overhead. StringBuffer is also thread-safe but slightly slower due to synchronization. String creates a new string each time you modify it, and StringJoiner is used for joining strings, not efficient for concatenation.

In Java, the dollar sign ($) is not a valid operator. It's used in variable names and identifiers but not as an operator. The other options (+, -, %) are valid arithmetic operators in Java.

In Java 8 and above, the "forEach()" method is used to perform a specified action for each element of a collection. It provides a concise way to iterate through elements in a collection and apply a given action to each element. The other options do not represent the correct method for this purpose.

Intrinsic locking in synchronized methods/blocks ensures thread safety by preventing multiple threads from executing synchronized code simultaneously. When a thread enters a synchronized block, it acquires the lock associated with the synchronized object, preventing other threads from entering the same synchronized block until the lock is released. This ensures that only one thread can execute the synchronized code at a time, preventing data races and ensuring thread safety.

When you try to execute a DML operation (such as INSERT, UPDATE, DELETE) using the executeQuery() method, option b is correct. It will throw a SQLException because executeQuery() is meant for querying data and returns a ResultSet, which is not applicable to DML operations. Options a and c are incorrect because they suggest that the DML operation can proceed, which is not the case. Option d is also incorrect; it does not represent the actual behavior of executeQuery().

The ObjectOutputStream class in Java is used to serialize objects into a byte stream. It's responsible for writing the state of an object to the output stream. Conversely, ObjectInputStream is used for reading serialized objects from a stream. It is an essential part of Java's serialization mechanism.

The primary difference is that StringBuilder is not synchronized, making it faster but not thread-safe, while StringBuffer is synchronized, making it thread-safe but potentially slower. Immutable means unchangeable, which is not true for either class.