Best Core Java Interview Questions and Answers

Core Java is the fundamental part of the Java programming language, including syntax, libraries, and basic concepts essential for development. Below are are some of the Best Core Java Interview Questions and Answers.

1. What is Java?

• Answer: Java is a high-level, object-oriented programming language developed by Sun Microsystems. It is designed to be platform-independent and follows the principle of “Write Once, Run Anywhere” (WORA).

2. Explain the main features of Java.

• Answer: Key features of Java include:
  • Object-oriented
  • Platform-independent
  • Simple and easy to learn
  • Distributed computing support (RMI, EJB)
  • Multithreading
  • Robust and secure
  • Dynamic and interpreted

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

• Answer:
  • JVM (Java Virtual Machine): It is the runtime environment for Java applications, responsible for executing Java bytecode.
  • JRE (Java Runtime Environment): It includes JVM, libraries, and other components necessary for running Java applications, but it does not include development tools.
  • JDK (Java Development Kit): It contains JRE and development tools like compiler and debugger.

4. What is the difference between == and equals method?

• Answer:
  • == is used to compare object references, i.e., whether two references point to the same memory location.
  • equals method is used to compare the content or values of objects. It needs to be explicitly overridden in the class to provide meaningful comparison.

5. Explain the concept of multithreading in Java.

• Answer: Multithreading in Java allows multiple threads of execution to run concurrently. It is a way to achieve parallelism and can improve the performance of a program. Threads are lightweight processes, and Java provides the Thread class and the Runnable interface for creating and managing threads.

6. What is the Java Collections Framework?

• Answer: The Java Collections Framework provides a set of classes and interfaces for handling and manipulating collections of objects. It includes interfaces like List, Set, and Map, along with their implementations like ArrayList, HashSet, and HashMap.

7. Explain the difference between ArrayList and LinkedList.

• Answer:
  • ArrayList: It uses a dynamic array to store elements. It is good for random access but not efficient for frequent insertions and deletions.
  • LinkedList: It uses a doubly-linked list, making it efficient for insertions and deletions but less efficient for random access.

8. What is the purpose of the finalize method in Java?

• Answer: The finalize method is called by the garbage collector before reclaiming the memory occupied by an object. It can be used to perform cleanup operations or release resources before the object is garbage collected.

9. What is the difference between throw and throws in Java?

• Answer:
  • throw: It is used to explicitly throw an exception within a method or block of code.
  • throws: It is used in method signatures to declare the exceptions that the method might throw. It informs the caller about potential exceptions.

10. Explain the concept of JavaBeans.

• Answer: JavaBeans are reusable software components for Java that follow certain design conventions. They are used to encapsulate and organize functionality into modular, reusable units. JavaBeans are often employed in building graphical user interfaces (GUIs) and are identifiable by their properties, methods, and events.

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