In Java, a parameterized constructor is used to initialize instance variables with values provided as arguments during object creation. This allows objects to be created with different initial states. Option 1 is incorrect as the default constructor initializes class-level variables, not parameterized constructors. Options 2 and 4 are not accurate descriptions of parameterized constructors.

To run a for-each loop in parallel and utilize multiple cores/threads in Java, you can use the Java Stream API and the parallelStream() method on the collection. Option 2 correctly describes this approach. Option 1 involves manual thread management, Option 3 suggests creating a custom method, and Option 4 is not entirely accurate; Java does not automatically parallelize for-each loops.

A for loop is suitable when you have a known number of iterations, but a while loop is more appropriate when the loop termination condition depends on complex criteria that may not be easily expressed in a for loop's initialization and condition. Option 2 correctly identifies this scenario. Option 1 is not entirely accurate as for loops can also iterate over collections. Options 3 and 4 do not directly relate to the suitability of for loops compared to while loops.

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.

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.

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 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.

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 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.

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.

A Callable in Java is a result-bearing computation that can be canceled and can compute the result asynchronously. It is typically used with ExecutorService to perform tasks that return values or throw exceptions.

To securely serialize and deserialize objects to protect sensitive information, you should use encryption techniques. Encrypting the data before serialization and decrypting it after deserialization ensures that the data remains confidential. While access modifiers and marking classes as final provide some level of security, they don't directly address the need for encryption. Custom logic with encryption and authentication is a comprehensive approach to security.