Java Developer interview questions

Java 8 and later versions introduced features such as lambda expressions, the Stream API, functional interfaces, method references, default and static methods in interfaces, the new Date and Time API, and enhancements to concurrency utilities. These features improve code readability, enable functional programming paradigms, and increase developer productivity and performance in enterprise-grade applications.

Object-oriented programming in Java enables encapsulation, inheritance, polymorphism, and abstraction, which leads to modular code, reusability, improved maintainability, and scalability. By modeling real-world entities as objects with state and behavior, and using inheritance for hierarchical relationships, developers can easily adapt and extend applications over time with minimal code changes.

Thread safety in Java is achieved through techniques such as synchronization, the use of volatile variables, concurrent collections, atomic classes, the Java Memory Model, and immutability. Advanced strategies include leveraging thread-local variables and high-level constructs like ReentrantLock, ReadWriteLock, and Executors framework to manage and control thread access to shared resources.

Lambda expressions provide a clear and concise way to represent single-method interfaces (functional interfaces) using an arrow syntax. This reduces boilerplate code in collections processing, event handling, and parallel operations via the Stream API, improving both code readability and potential performance through built-in optimizations such as laziness and parallel stream support.

Best practices include minimizing shared mutable state, using thread-safe data structures, applying synchronization or locks only when necessary, preferring higher-level concurrency utilities, following the principle of fail-fast in collection iteration, and thoroughly testing under load for deadlocks and race conditions. Immutable classes and thread confinement are frequently used to simplify concurrency.

The Stream API enables functional-style processing of collections, allowing declarative data manipulation such as filtering, mapping, and reducing. It abstracts away iteration details, supports pipelined operations for efficiency, and enables parallel execution for improved performance on multi-core systems. This leads to cleaner and more maintainable data processing code.

Immutability ensures that an object's state cannot be changed after creation, making it inherently thread-safe. Immutable objects can be shared freely between threads without synchronization, reducing the risk of race conditions, eliminating side effects, and simplifying concurrent program design and reasoning.

Synchronized blocks are simple to use and prevent multiple threads from accessing code sections simultaneously, but can be inflexible and cause contention. Locks, such as those provided by java.util.concurrent.locks, offer more control (e.g., tryLock, timed lock), fairness, and interruptibility. Atomic variables, provided by java.util.concurrent.atomic, support lock-free thread-safe operations on single variables and are best for simple scenarios requiring high performance.

Functional interfaces are interfaces with a single abstract method, which serve as the target types for lambda expressions and method references. Standard functional interfaces like Predicate, Function, Consumer, and Supplier are extensively used in the Stream API, collections API, and for defining concise behaviors as parameters, reducing verbosity and improving code flexibility.

The Executor framework provides a high-level API for managing thread pools and asynchronous task execution. With interfaces like Executor, ExecutorService, and ScheduledExecutorService, developers can decouple task submission from thread management, optimize resource utilization, configure thread pool policies, handle future results, and improve the reliability and scalability of Java applications dealing with concurrency.