In a scenario where an application needs to handle a large number of JDBC connections concurrently, how would you optimize the use and management of these connections to ensure application performance is not impacted?
- Increase the maximum connection limit in the database server configuration.
- Open a new database connection for each user request to ensure isolation.
- Use a connection pool to manage connections, limiting the number of active connections and reusing them efficiently.
- Use the default JDBC connection management without any special optimization.
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 method overriding, the return type must be the same or a ________ of the superclass overridden method's return type.
- child
- different
- subclass
- superclass
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.
How can you customize the serialization process to handle custom object serialization?
- Define the writeObject and readObject methods
- Implement the Serializable interface
- Use the static modifier for all fields
- Use the transient keyword to exclude fields from serialization
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.
How is method overloading resolved when there is an ambiguity in method signatures?
- The JVM randomly selects one of the overloaded methods.
- The compiler throws an error and asks for explicit casting of parameters.
- The method with the least specific parameter types is chosen.
- The method with the most specific parameter types is chosen.
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.
The method ________ is used to return the hash code value for a Map.
- getHashcode()
- hashCode()
- hashValue()
- mapHash()
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.
What keyword is used to extend a class in Java?
- extends
- implements
- inherits
- subclass
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 ________ and provides methods to schedule commands to run after a given delay or to execute periodically.
- Callable
- ExecutorService
- Future
- Runnable
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.
If a class implements two interfaces with default methods having the same signature, the compiler will throw an error unless the class ________ the conflicting method.
- abstracts
- hides
- overrides
- renames
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.
Which class in JavaFX provides the capability to update the UI from a thread other than the JavaFX application thread?
- Platform
- javafx.application.Application
- javafx.concurrent.Service
- javafx.concurrent.Worker
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 is used to control the access of multiple threads to any ________.
- class
- exception handling block
- method or class
- variable or object
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.