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 Java, method overriding occurs when a subclass provides a specific implementation for a method that is already defined in its superclass. Therefore, it is not possible to override a method in the same class because there is no superclass-subclass relationship. However, you can overload methods within the same class by defining methods with the same name but different parameter lists.

The term you're looking for is "Functional." In Java, Lambda expressions can be assigned to functional interfaces, which act as a type for lambda expressions. These interfaces typically define a single abstract method that the lambda expression implements. This allows lambda expressions to be treated as if they were a type, and they can be passed as parameters to methods, returned from methods, or stored in variables.

To manage and transfer data between scenes in a JavaFX application, it's best to use a centralized data model or service. This approach ensures data consistency and makes it easier to share data between different scenes. Serializing data objects, global variables, and file operations are less suitable for preserving data between scenes.

In a high-concurrency scenario, using a connection pool is a best practice. It helps manage connections efficiently by reusing them and limiting the number of active connections. This minimizes the overhead of creating and closing connections, ensuring optimal performance. Increasing the connection limit in the database server can lead to resource exhaustion. Opening a new connection for each request is inefficient and can overload the database server. Using default JDBC connection management may not be suitable for handling a large number of concurrent connections.

In Java, when you override a method, the return type of the overriding method must be the same as or a subclass of the return type of the overridden method in the superclass. This is known as covariant return types.

In Java, you can customize the serialization process for custom objects by defining the writeObject and readObject methods. These methods allow you to have fine-grained control over how the object is serialized and deserialized. You can implement custom logic to handle complex objects or sensitive data. The other options are essential but do not provide customization for custom object serialization.

In Java, when there is an ambiguity in method signatures during method overloading, the compiler chooses the method with the most specific parameter types. Specificity is determined by the inheritance hierarchy, with the most specific type being favored. This ensures that the correct method is called based on the arguments provided.

In Java, the hashCode() method is used to return the hash code value for an object. In the context of a Map, this method is often used to calculate the hash code for keys, which is crucial for efficient storage and retrieval in hash-based data structures like HashMap and Hashtable. The other options are not standard methods for obtaining hash codes.

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.