Parameterized constructors can be utilized in a user profile management system to quickly initialize user objects during the registration process. These constructors accept user details (e.g., username, email, password) as parameters, allowing you to create user objects with pre-populated data, making registration more efficient and straightforward.

Lambda expressions in Java are primarily used to define the implementation of functional interfaces. A functional interface is an interface that has only one abstract method. Lambda expressions provide a concise way to implement the single abstract method of such interfaces.

The expression 5 > 3 is true because 5 is indeed greater than 3. The other options are not true: 10 != 10 is false (since 10 is equal to 10), (4 + 6) * 2 == 20 is true (since 10 equals 20), and "Java" == "java" is false because string comparison in Java is case-sensitive.

The Runnable interface in Java can be implemented using lambda expressions. It's a functional interface with a single abstract method run(). This allows you to use lambda expressions for tasks that can be executed concurrently. Lambda expressions simplify the creation of anonymous classes for such tasks.

In Java, when you try to override a method from a superclass in a subclass, the method in the superclass must exist; otherwise, it will lead to a compile-time error. Java enforces method signature matching during compile-time, so if the method doesn't exist in the superclass, the compiler will not find a method to override in the subclass, resulting in an error.

The getMessage() method of the Throwable class is used to retrieve the description or message associated with an exception. This message provides additional information about the exception, helping developers understand the cause of the error.

The FileWriter class in Java is used to write characters to a file. It provides methods to write character data to a file in a character stream. FileOutputStream is used for writing binary data, PrintWriter is used for formatted text output, and BufferedReader is used for reading character data, not writing.

The "start()" method is used to move a thread into the Ready/Runnable state in Java. When a thread is started using "start()", it becomes eligible for execution, and the JVM schedules it for execution at the appropriate time.

The JavaFX Application Thread, also known as the JavaFX UI thread, is responsible for managing the user interface (UI) and handling user input events in a JavaFX application. It ensures that UI updates and event handling are done in a thread-safe manner, preventing UI freezes and glitches. This thread is crucial for providing a responsive and smooth user experience in JavaFX applications.

In Java, when you use the + operator with both numbers and strings, it performs left-to-right addition. So, the numbers are added first, and then the result is concatenated with the strings. The correct output is "1020Hello3040."