30+ 10405090xyzabc Interview Questions and Answers

ArrayList offers fast access and is memory efficient, while LinkedList excels in insertions and deletions.

• ArrayList allows O(1) access time, making it ideal for frequent retrievals. Example: Accessing elements in a list of user IDs.

• LinkedList provides O(1) time for insertions/deletions at both ends. Example: Implementing a queue where elements are frequently added/removed.

• Memory overhead in LinkedList is higher due to extra pointers for each node, which can be significant in ...read more

Checked exceptions require handling; unchecked exceptions do not. Custom exceptions can be either, based on use case.

• Checked exceptions must be handled with try-catch or declared with throws.

• Examples of checked exceptions: IOException, SQLException.

• Unchecked exceptions do not require explicit handling.

• Examples of unchecked exceptions: NullPointerException, ArithmeticException.

• Use checked exceptions for recoverable conditions; unchecked for programming errors.

• Custom exceptions...read more

Immutability in Java ensures objects cannot be modified after creation, enhancing thread safety and reducing side effects.

• Immutable objects cannot be changed once created, e.g., String class in Java.

• Thread-safe: Since they cannot be modified, they prevent issues in multi-threaded environments.

• Prevent unintended side effects, making code easier to understand and maintain.

• To create an immutable class, use final fields and avoid setter methods.

• Collections can be made immutable u...read more

Singleton pattern ensures a class has only one instance, providing a global access point for shared resources.

• Private constructor prevents instantiation from outside the class.

• Static instance variable holds the single instance of the class.

• Lazy initialization creates the instance only when needed.

• Eager initialization creates the instance at class loading time.

• Thread safety can be achieved using synchronized methods or blocks.

• Double-checked locking minimizes synchronization ov...read more

== checks reference equality; .equals() checks value equality, can be overridden for custom comparison.

• == compares memory addresses, while .equals() compares actual content.

• Example: new String("hello") == new String("hello") returns false.

• "hello".equals("hello") returns true.

• Wrapper classes like Integer cache small values, affecting == behavior.

• Override equals() when logical equality is needed, e.g., in custom classes.

• When overriding equals(), also override hashCode() to main...read more

The Java Memory Model defines thread interaction with memory, ensuring visibility and ordering in multithreaded environments.

• JMM specifies how threads interact with shared variables, ensuring visibility and ordering.

• Volatile keyword ensures that changes to a variable are visible to all threads immediately.

• Synchronized blocks provide mutual exclusion, preventing multiple threads from accessing critical sections simultaneously.

• Without synchronization, threads may read stale or ...read more

Java Streams enable functional operations on collections with lazy evaluation, differing from Iterators in several key aspects.

• Streams support functional-style operations like filter(), map(), and reduce() for cleaner code.

• Example: list.stream().filter(x -> x > 10).collect(Collectors.toList()) filters elements greater than 10.

• Streams are not reusable; once consumed, they cannot be used again.

• Iterators can be reset and reused, allowing for multiple traversals of the same colle...read more

Lambda expressions enhance Java code by making it more concise, readable, and easier to maintain through functional programming.

• Conciseness: Lambda expressions reduce boilerplate code. For example, instead of writing an anonymous class for a Runnable, you can use: `Runnable r = () -> System.out.println("Hello");`

• Readability: They allow for clearer expression of intent. For instance, using `list.forEach(item -> System.out.println(item));` is more straightforward than using a l...read more

Method overloading allows same method name with different parameters; overriding allows subclass to redefine parent method.

• Method Overloading: Same method name, different parameters (e.g., `int add(int a, int b)` and `double add(double a, double b)`)

• Method Overriding: Subclass provides specific implementation of a method defined in its superclass (e.g., `void display()` in parent and `void display()` in child)

• Overloading is resolved at compile time (static binding), while ove...read more

Functional interfaces in Java enable lambda expressions for concise implementation of single abstract methods.

• A functional interface has exactly one abstract method, e.g., Runnable, Callable.

• Lambda expressions provide a shorthand way to implement functional interfaces, e.g., () -> System.out.println("Hello").

• Functional interfaces can have multiple default or static methods, allowing for added functionality without breaking existing code.

• The @FunctionalInterface annotation ens...read more

Java annotations provide metadata for classes, enhancing readability and reducing boilerplate in frameworks like Spring.

• Annotations like @Component and @Service simplify bean management in Spring.

• Dependency injection is streamlined with @Autowired, reducing manual wiring.

• Custom annotations can encapsulate repetitive configurations, improving code clarity.

• Annotations like @Transactional manage database transactions declaratively.

• Built-in annotations like @Override enhance code...read more

Java Streams enable parallel processing using ForkJoin framework, but have pitfalls like race conditions and performance issues with small datasets.

• Use parallel streams for CPU-intensive tasks to leverage multiple cores effectively.

• Avoid using parallel streams for small datasets as overhead may outweigh benefits.

• Be cautious of shared mutable state to prevent race conditions; prefer immutable data structures.

• Use forEachOrdered() for order-sensitive operations, but be aware it ...read more

Java's garbage collector automatically manages memory, reclaiming space from unused objects through various algorithms.

• Garbage collection in Java is automatic, freeing developers from manual memory management.

• The JVM uses different GC algorithms: Serial, Parallel, CMS, and G1 GC, each with unique characteristics.

• Memory is divided into regions: Young Generation (short-lived objects), Old Generation (long-lived objects), and PermGen/Metaspace (class metadata).

• Minor GC occurs in...read more

final, finally, and finalize serve different purposes in Java: constants, cleanup, and garbage collection respectively.

• final: Used to declare constants. Example: final int MAX_VALUE = 100;

• final: Prevents method overriding. Example: final void display() {}

• final: Prevents inheritance. Example: final class Constants {}

• finally: Executes after try-catch for cleanup. Example: try { ... } catch { ... } finally { closeResources(); }

• finalize(): Method called by garbage collector. Exam...read more

ArrayList and LinkedList are both implementations of the List interface in Java. ArrayList uses a dynamic array to store elements, while LinkedList uses a doubly linked list.

• ArrayList is faster for accessing elements by index, while LinkedList is faster for adding or removing elements in the middle of the list.

• ArrayList uses more memory as it needs to allocate space for the entire list upfront, while LinkedList only needs memory for each element and its pointers.

• Choose ArrayL...read more

Java Stream is a sequence of elements that supports functional-style operations. It differs from Iterator by allowing for more concise and declarative code.

• Streams provide a way to process collections in a functional programming style, allowing for operations like map, filter, and reduce.

• Unlike Iterators, Streams do not store elements, making them more memory efficient.

• Streams can be parallelized to take advantage of multi-core processors for faster processing.

• Example: List<S...read more

Immutability in Java means that an object's state cannot be changed after it is created. String class achieves immutability by not allowing its value to be modified.

• Immutability means that once an object is created, its state cannot be changed.

• String class achieves immutability by making its value final and not providing any methods to modify it.

• Advantages of immutable objects include thread safety, caching, and easier debugging.

final, finally, and finalize have different meanings in Java.

• final is a keyword used to declare constants, immutable variables, or prevent method overriding.

• finally is a block used in exception handling to execute code after try-catch block.

• finalize is a method used for cleanup operations before an object is garbage collected.

Singleton design pattern ensures a class has only one instance and provides a global point of access to it.

• Create a private static instance of the class.

• Make the constructor private to prevent instantiation from outside the class.

• Provide a public static method to access the instance, creating it if necessary.

• Use synchronized keyword or double-checked locking to ensure thread safety.

Method overloading involves creating multiple methods in the same class with the same name but different parameters. Method overriding involves creating a method in a subclass that has the same name, return type, and parameters as a method in the superclass.

• Method overloading is used to provide different implementations of a method based on the number or type of parameters passed.

• Method overriding is used to provide a specific implementation of a method in a subclass that is ...read more

Java annotations are metadata that provide data about a program but do not affect the program itself. They are used in frameworks like Spring to simplify configuration and reduce boilerplate code.

• Java annotations are used to provide metadata about classes, methods, fields, etc. They are defined using the @ symbol.

• In Spring framework, annotations are used to configure various aspects of the application, such as dependency injection, transaction management, and MVC mappings.

• Bui...read more

Using Java's synchronized keyword for thread synchronization has advantages like simplicity and disadvantages like potential deadlock. ReentrantLock offers more flexibility and control.

• Advantages of synchronized keyword: easy to use, built-in support in Java

• Disadvantages of synchronized keyword: potential for deadlock, lack of flexibility

• ReentrantLock advantages: more control over locking, ability to try and acquire lock, support for condition variables

• ReentrantLock disadvant...read more

The Java garbage collector automatically manages memory by reclaiming unused objects.

• Garbage collector runs in the background to reclaim memory from objects no longer in use.

• Different types of garbage collection algorithms include Serial, Parallel, CMS, G1, and ZGC.

• Serial collector is best for single-threaded applications, while G1 is suitable for large heap sizes.

• CMS (Concurrent Mark Sweep) collector minimizes pause times by running most of the collection concurrently with t...read more

The Java Memory Model defines how threads interact through memory and how changes made by one thread are visible to others.

• Java Memory Model specifies how threads interact with memory, ensuring visibility and consistency.

• It defines the rules for reading and writing variables in a multithreaded environment.

• Synchronization ensures that only one thread can access a shared resource at a time.

• Volatile keyword in Java ensures visibility of changes made by one thread to other thread...read more

Java Streams can handle parallel processing using parallel streams. Pitfalls include increased complexity and potential for race conditions.

• Java Streams can utilize parallel processing by using parallel streams, which automatically divide the data into multiple chunks and process them concurrently.

• Potential pitfalls of using parallel streams include increased complexity, potential for race conditions, and overhead of managing parallel threads.

• To mitigate these pitfalls, ensur...read more

In Java, == compares memory addresses while .equals() compares values. Improper usage can lead to unexpected results.

• Use == to compare primitive data types and object references.

• Use .equals() to compare the actual values of objects.

• Improper usage of == with objects can lead to comparing memory addresses instead of values.

• Improper usage of .equals() can lead to NullPointerException if used with null objects.

Java 8 introduced features like lambdas and Stream API which have revolutionized the way Java applications are written.

• Lambdas allow for more concise and readable code by enabling functional programming paradigms.

• Stream API provides a way to process collections of objects in a functional style, allowing for easier parallel processing and improved performance.

• Java 8 also introduced default methods in interfaces, allowing for backward compatibility with existing code while stil...read more

Functional interfaces in Java are interfaces with a single abstract method. They can be used with lambda expressions for functional programming.

• Functional interfaces have only one abstract method, but can have multiple default or static methods.

• Lambda expressions can be used to implement the single abstract method of a functional interface concisely.

• An example of a custom functional interface is 'Calculator' with a single abstract method 'calculate'.

Checked exceptions are checked at compile time, while unchecked exceptions are not. Proper handling involves either catching or declaring the exception.

• Checked exceptions must be either caught or declared in the method signature using 'throws'. Example: IOException.

• Unchecked exceptions do not need to be caught or declared. Example: NullPointerException.

• Proper handling of exceptions involves using try-catch blocks for checked exceptions and ensuring null checks for potential u...read more

A use case diagram is a visual representation of the interactions between users and a system, showing the various use cases and actors involved.

• Use case diagrams are typically utilized in software development to capture the functional requirements of a system.

• They help in identifying the different ways users can interact with the system and the various scenarios that can occur.

• Use case diagrams show the relationships between actors (users) and use cases, helping in understand...read more

A transaction in DBMS is a unit of work that must be executed as a whole. ACID properties ensure data integrity. SQL is relational, NoSQL is non-relational.

• A transaction in DBMS is a set of operations that must be executed as a single unit.

• ACID properties (Atomicity, Consistency, Isolation, Durability) ensure data integrity in transactions.

• SQL databases are relational and use structured query language, while NoSQL databases are non-relational and offer more flexibility.

• To opt...read more

Encapsulation is the concept of bundling data and methods that operate on the data into a single unit. Inheritance allows a class to inherit attributes and methods from another class. Polymorphism allows objects of different classes to be treated as objects of a common superclass.

• Encapsulation helps in data hiding and abstraction

• Example: A class 'Car' encapsulates data like make, model, and methods like start(), stop()

• Inheritance allows for code reusability and promotes the c...read more

Use Floyd's Tortoise and Hare algorithm to detect a cycle in a linked list.

• Start with two pointers, slow and fast, moving at different speeds.

• If there is a cycle, the two pointers will eventually meet at some point.

• If there is no cycle, the fast pointer will reach the end of the list.

• Example: 1->2->3->4->5->2 (cycle at node 2), slow and fast pointers will meet at node 2.

A use case diagram is a visual representation of the interactions between users and a system, showing the different ways users can interact with the system.

• Use case diagrams are typically used in software development to capture the functional requirements of a system.

• They help in identifying the actors (users) and their interactions with the system.

• Use case diagrams show the various use cases or scenarios in which the system can be used.

• They are useful for communicating syste...read more