In Java, only reference data types (objects) can store a null value. Among the given options, String is a reference data type that can store null. The other options are primitive data types and cannot hold null values.

The main challenge of implementing operator overloading in Java is ambiguity. Operator overloading can lead to confusion and unintended behavior, making the code less readable and maintainable. Since Java doesn't support operator overloading for user-defined classes, developers are encouraged to use meaningful method names instead.

Merge Sort is a sorting algorithm that uses a divide-and-conquer strategy. It divides the unsorted list into smaller sublists, sorts those sublists, and then merges them to obtain the final sorted list. This approach results in better performance compared to some other sorting algorithms.

In JavaFX, managing multiple events efficiently is crucial for performance. Using event delegation by handling events at a higher-level parent node minimizes the number of event listeners, reducing overhead. This is a common best practice in JavaFX game development. Increasing the frame rate alone won't solve performance issues and may lead to excessive resource consumption. Using a single event handler is less efficient than event delegation, and attaching listeners to each object increases overhead.

The do-while loop is designed to execute its code block at least once, as it checks the condition after executing the loop body. This is useful when you want to ensure that a piece of code runs before checking the condition for termination.

The write method of the FileOutputStream class is used to write a specific byte of data to a file output stream. You can use this method to write individual bytes or byte arrays to a file.

In Java, the default constructor is a constructor provided by Java for every class that doesn't explicitly define its own constructor. It takes no parameters and initializes instance variables to their default values. The other options do not accurately describe the default constructor in Java.

To restrict the usage of certain methods to the external world while allowing them to be used within the package, you would use the package-private access modifier. This is achieved by not specifying any access modifier (default) before the method declaration. Public methods are accessible from anywhere, private methods are restricted to the class, and protected methods allow access within the package and subclasses.

Java does not support operator overloading primarily to simplify the language and reduce complexity. Operator overloading can lead to ambiguity in code, making it harder to read and maintain. Instead, Java encourages method overloading as a way to achieve similar functionality.

Wrapper collection classes (such as ArrayList) store objects, while Primitive collection classes (such as ArrayList) store primitive data types directly. The wrapper classes allow primitive data types to be used in collections that require objects.