Top Core Java Interview Questions for Experienced Developers

As a seasoned Java developer with number of years of experience under your belt, you’re likely well-versed in the fundamentals and intricacies of Java programming. However, facing an interview can still be nerve-wracking, especially when you’re expected to demonstrate your expertise in core Java concepts. To help you prepare, let’s delve into some of the top core Java interview questions that you may encounter during your job search.

1.            What is the difference between JDK, JRE, and JVM?

•             JDK (Java Development Kit): It is a software development kit used for developing Java applications. It includes the JRE, compiler, debugger, and other tools needed for development.

•             JRE (Java Runtime Environment): It provides the runtime environment for Java applications. It includes the JVM and libraries required to run Java applications but does not include development tools.

•             JVM (Java Virtual Machine): It is an abstract computing machine that provides the runtime environment in which Java bytecode can be executed. It is platform-dependent and converts bytecode into machine code.

2.            What are the important features introduced in Java 8?

•             Lambda Expressions: Enable functional programming style in Java.

•             Stream API: Facilitates processing collections of objects in a functional manner.

•             Default and Static Methods in Interfaces: Allows interfaces to have methods with default implementations.

•             Optional Class: Helps in handling null values more effectively.

•             Date and Time API: Provides a comprehensive API for date and time manipulation.

3.            Explain the concept of multithreading in Java. How is it achieved?

Multithreading allows concurrent execution of multiple threads within a single process. In Java, multithreading is achieved by extending the Thread class or implementing the Runnable interface. Threads can run concurrently, allowing developers to perform multiple tasks simultaneously and utilize the available CPU resources efficiently.

4.            What are the different types of inheritance in Java?

•             Single Inheritance: A class inherits from only one superclass.

•             Multilevel Inheritance: A derived class inherits from a superclass, and another class derives from this derived class.

•             Hierarchical Inheritance: Multiple classes inherit from a single superclass.

•             Multiple Inheritance (through interfaces): A class can implement multiple interfaces, effectively achieving multiple inheritance.

5.            What is the purpose of the finalize() method?

The finalize() method is called by the garbage collector before an object is garbage collected. It gives the object an opportunity to perform any necessary cleanup operations before it is reclaimed by the JVM.

6.            What is the difference between == and .equals() method in Java?

•             The == operator is used to compare the references of two objects.

•             The .equals() method is used to compare the contents or values of two objects. It is usually overridden in classes to provide meaningful comparison logic.

7.            Explain the concept of exception handling in Java.

Exception handling in Java allows developers to deal with runtime errors or exceptional conditions gracefully. It involves the use of try, catch, finally, and throw keywords. Exceptions can be categorized into checked exceptions (which are checked at compile time) and unchecked exceptions (which are not checked at compile time).

8.            What is the difference between ArrayList and LinkedList?

•             ArrayList is implemented as a resizable array, whereas LinkedList is implemented as a doubly linked list.

•             ArrayList provides faster access to elements using index-based retrieval, while LinkedList provides faster insertion and deletion operations, especially for large lists.

9.            How does garbage collection work in Java?

Garbage collection in Java is the process of automatically reclaiming memory occupied by objects that are no longer reachable or in use by the program. The JVM’s garbage collector periodically identifies and removes such objects to free up memory and prevent memory leaks.

10.          What is the purpose of the transient keyword in Java?

The transient keyword is used to indicate that a variable should not be serialized when the object containing it is serialized. It is commonly used for sensitive or unnecessary data that should not be persisted.

These are just a few examples of the types of questions you may encounter during a core Java interview for a experienced developer. Remember to not only memorize the answers but also understand the underlying concepts thoroughly. Good luck with your interview preparations!

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