In Java, the extends keyword is used to indicate inheritance and extend a class. When a class extends another class, it inherits all the members (fields and methods) of the parent class, allowing you to create a subclass that inherits and extends the functionality of the superclass.

The ScheduledExecutorService interface extends the ExecutorService interface in Java. It provides additional methods for scheduling tasks to run after a specified delay or at regular intervals. This is a useful feature for implementing scheduled tasks or background jobs in applications.

In Java, if a class implements two interfaces with default methods having the same signature, it must provide an implementation for the conflicting method by using the @Override annotation to explicitly indicate that it is intended to override the method. This resolves the conflict and prevents a compilation error. Renaming, hiding, or making it abstract won't resolve the issue.

In JavaFX, the javafx.concurrent.Worker class provides the capability to update the UI from a thread other than the JavaFX application thread. It's commonly used for performing background tasks and updating the UI accordingly. The other options are not designed for this specific purpose.

The synchronized keyword in Java can be used to control the access of multiple threads to either a method or a block of code within a class. It ensures that only one thread can enter the synchronized block or method at a time, preventing concurrent access and potential data corruption or race conditions. Synchronized methods and blocks are used to achieve thread safety in multi-threaded Java applications.

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.