Java continues to be one of the most sought-after programming languages in the IT industry, especially in companies like Accenture. Java's robustness, scalability, and platform independence make it ideal for building enterprise-level applications. If you're preparing for a Java Developer interview at Accenture, this blog will provide you with the most commonly asked Java interview questions along with answers to help you confidently ace the interview.
1. What are the key features of Java?
Java is known for being platform-independent, object-oriented, secure, multithreaded, robust, and having automatic memory management through garbage collection.
2. Explain the OOP principles in Java.
Java is based on four core object-oriented principles:
- Encapsulation: Bundling data and methods that operate on that data into a single unit or class.
- Inheritance: Mechanism by which one class inherits the properties and behavior of another class.
- Polymorphism: Ability to process objects differently based on their data type or class.
- Abstraction: Hiding the implementation details and showing only the functionality.
3. What is the JVM, JRE, and JDK?
- JVM (Java Virtual Machine): A virtual machine that runs Java bytecode on different platforms.
- JRE (Java Runtime Environment): Provides libraries, JVM, and other components necessary to run Java applications.
- JDK (Java Development Kit): A full-featured software development kit to develop Java programs, including JRE, compilers, and tools.
4. Can you explain the concept of a class and an object in Java?
- Class: A blueprint from which individual objects are created. It defines properties (fields) and methods.
- Object: An instance of a class with concrete values for its fields.
5. What are access modifiers in Java?
Access modifiers control the visibility and accessibility of classes, methods, and variables. They are:
- Private: Accessible only within the same class.
- Default: Accessible within the same package.
- Protected: Accessible within the same package or subclasses.
- Public: Accessible from anywhere.
6. What is the difference between == and .equals() in Java?
==: Compares references (memory addresses) of objects, meaning it checks if two objects point to the same memory location..equals(): Compares the actual content of objects, typically used to compare the values of two objects.
7. What is the Java Collections Framework?
The Java Collections Framework is a set of classes and interfaces that implement commonly reusable data structures like Lists, Sets, Maps, and Queues. It provides algorithms to perform operations such as searching, sorting, and modifying collections.
8. Explain the difference between ArrayList and LinkedList in Java.
- ArrayList: A resizable array that offers fast random access and is better for read-heavy operations.
- LinkedList: A doubly linked list that offers fast insertion and deletion at any position but slower random access.
9. What is the difference between HashMap and TreeMap?
- HashMap: Stores key-value pairs with no guaranteed order. It uses hashing to achieve constant-time performance for basic operations.
- TreeMap: Stores key-value pairs in sorted order, following the natural order of keys or a specified comparator. Performance is O(log n).
10. How does Java handle memory management?
Java uses automatic memory management through the Garbage Collector. The Garbage Collector automatically deletes objects that are no longer referenced, freeing memory.
11. What is multithreading in Java, and how is it implemented?
Multithreading in Java is the concurrent execution of two or more threads. It can be implemented by either:
- Extending the
Threadclass and overriding itsrun()method. - Implementing the
Runnableinterface and passing it to aThreadobject.
12. Explain the difference between synchronized and volatile in Java.
- synchronized: A keyword that prevents multiple threads from accessing a block of code simultaneously, ensuring thread safety.
- volatile: A keyword that tells the JVM that a variable can be modified by different threads, so it should not cache the value.
13. What is the difference between final, finally, and finalize() in Java?
- final: A keyword used to declare constants, prevent method overriding, or prevent inheritance of a class.
- finally: A block used in exception handling to execute code regardless of whether an exception is thrown or not.
- finalize(): A method invoked by the Garbage Collector before reclaiming an object’s memory.
14. What are the types of exceptions in Java?
There are two types:
- Checked Exceptions: Checked at compile-time, such as
IOException. - Unchecked Exceptions: Checked at runtime, such as
ArrayIndexOutOfBoundsException.
15. What is a thread-safe class in Java?
A thread-safe class ensures that its methods or blocks are executed by only one thread at a time, preventing race conditions. Examples include Vector, Hashtable, and synchronized collections.
16. What are functional interfaces in Java?
A functional interface is an interface with only one abstract method, annotated with @FunctionalInterface. It can be implemented using lambda expressions. Example: Runnable, Comparator, and Callable.
17. What is the Stream API in Java 8?
The Stream API allows for functional-style operations on collections, such as filtering, mapping, and reducing. It makes it easier to perform bulk data operations.
18. What is the difference between Iterator and ListIterator in Java?
- Iterator: Allows traversing elements in a forward direction.
- ListIterator: Allows traversing in both directions (forward and backward) and allows modification of elements during iteration.
19. What are design patterns in Java? Can you name a few?
Design patterns are standard solutions to common software design problems. Some common design patterns in Java are:
- Singleton: Ensures a class has only one instance.
- Factory: Creates objects without specifying the exact class.
- Observer: Allows a subject to notify observers when its state changes.
20. How does Java handle exception propagation?
When an exception occurs, it propagates up the call stack until it is caught or handled by an appropriate catch block. If it's not caught, it reaches the JVM, which terminates the program.
21. What is a lambda expression in Java, and how is it used?
Lambda expressions are introduced in Java 8 to enable functional programming. They allow you to write concise code by passing behavior (rather than objects) to methods.
List<String> names = Arrays.asList("Alice", "Bob", "Charlie");
names.forEach(name -> System.out.println(name));
22. What is the difference between Comparable and Comparator in Java?
- Comparable: Used to define the natural ordering of objects and is implemented by the object’s class.
- Comparator: Used to define an external ordering that can be used to compare objects in different ways.
23. Explain the use of the super keyword in Java.
The super keyword refers to the parent class object. It is used to:
- Access parent class methods and variables.
- Call the parent class constructor from the child class constructor.
24. What is transient keyword in Java?
The transient keyword in Java is used to mark fields that should not be serialized when an object is converted into a byte stream during serialization.
25. What is method overloading and method overriding in Java?
- Method Overloading: Defining multiple methods in a class with the same name but different parameters (compile-time polymorphism).
- Method Overriding: Redefining a method in a subclass that is already defined in the parent class (runtime polymorphism).
26. What is a deadlock, and how can it be avoided in Java?
A deadlock occurs when two or more threads are blocked forever, waiting for each other to release resources. It can be avoided by:
- Lock ordering: Always acquiring locks in the same order.
- Using timeout with
lock.tryLock(). - Avoiding unnecessary synchronization.
27. What is the difference between HashSet and TreeSet?
- HashSet: Stores unique elements with no defined order.
- TreeSet: Stores unique elements in sorted order.
28. What is a weak reference in Java?
A weak reference allows you to hold a reference to an object without preventing it from being garbage collected. This is useful in caching situations.
29. Explain the concept of pass-by-value in Java.
In Java, method arguments are always passed by value. This means that a copy of the variable is passed to the method, and any changes to the variable inside the method do not affect the original variable.
30. What is the purpose of static keyword in Java?
The static keyword in Java is used to define class-level variables or methods that can be accessed without creating an instance of the class.
Conclusion
These top 30 Java Developer interview questions and answers will help you prepare for your Accenture technical interview. Ensure you practice coding exercises and understand the underlying concepts thoroughly for a successful interview.
Good luck!
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