Looking to land your first job in Java programming? Time to ace the technical interview, and that means being well-prepared for beginner and advanced Java interview questions. In this article, we’ve compiled a list of top Java interview questions and answers that cover fundamental concepts, OOPs concepts, Exception Handling, Multithreading, and more. Whether you’re a beginner or an experienced professional, these frequently asked Java interview questions will help you gain a solid understanding of the language and increase your chances of landing your dream job. So, let’s dive in and explore the essential Java interview questions and answers that will help you impress your interviewers and demonstrate your skills as a Java developer.
Basic Java Interview Questions and Answers
Question 1. What is Java?
Answer – Java is a high-level language, a partially object-oriented programming language created in 1995 by Sun Microsystems. Java is known for its platform independence, which means that Java code can be written once and run on multiple platforms without the need for recompilation.
Question 2. What are the features of Java?
Answer – What’s unique about Java is that it offers higher cross-functionality as programs written in one platform can effortlessly be executed across different embedded systems. Here are the features that enable such functionality:
- High-Performance Runtime: With its Just in Time (JIT) compiler, Java offers high-performance runtime where the JIT compiler converts the Java bytecode into machine language code which is then executed by the JVM.
- Multi-Threading: When programs are run, a thread is a flow of execution, where JVM creates a thread which is denoted as the main thread. Java enables the execution of multiple threads by extending the thread class.
- OOPS Concepts: Object Oriented Programming in Java is an approach that enables modular programs with a partitioned memory area for both data and functions that can be used to create copies of similar modules.
- Platform Independency: Platform independency is one of the niche features of Java that utilizes the JVM or Java Virtual Machine to enable a single Java program to be executed on multiple platforms without changes.
Question 3. What is the difference between JDK, JRE, and JVM?
- JDK (Java Development Kit) is a development environment that includes everything needed to develop, debug, and run Java applications and applets.
- JRE (Java Runtime Environment) is a software package that includes the Java Virtual Machine (JVM) and required libraries needed to run Java applications.
- JVM is the component of the Java Runtime Environment (JRE) that executes Java bytecode.
Question 4. What is the difference between an object and a class?
Answer – A class is a blueprint or template for creating objects, while an object is an instance of a class.
Question 5. What is a constructor?
Answer – A constructor is a block of code in Java that initializes an object and sets initial values for attributes. Requiring the same name as that of a class, a constructor is called by default when an object is created and has no return type.
- Default Constructors: Default constructors, in Java, are the no-argument constructors to initialize instance variables, which will be created by default if any other constructor isn’t already defined by the programmer.
- Parameterized Constructors: Parameterized constructors, in Java, have a specific number of arguments to be passed and initialize instance variables with provided values. These are written explicitly by the coder.
Question 6. What is a variable?
Answer – A variable is a named memory location that stores a value that can be accessed and modified by a program.
Question 7. What is the difference between an instance variable and a class variable?
Answer – An instance variable is a variable that is associated with an instance of a class, while a class variable is a variable that is associated with the class itself.
Question 8. What is the difference between static and non-static methods?
Answer – Static methods are methods that are associated with a class, while non-static methods are methods that are associated with an instance of a class.
Question 9. What is an interface?
Answer – An interface is a collection of abstract methods that can be implemented by classes. It defines a contract that classes must follow to be considered compatible with the interface.
Question 10. What is an abstract class?
Answer – An abstract class is a class that cannot be instantiated and is intended to be subclassed. It can contain abstract methods, concrete methods, and instance variables.
Question 11. What feature in Java enables high performance? Explain the process?
Answer – With Just-in-Time compilation (JIT) compilation in Java, the bytecode is translated into machine code and then directly executed at runtime. To enable high performance, the JIT compiler is enabled by default which converts the bytecode of the Java method into native machine code, following which, the Java Machine Language calls the compiled code directly instead of interpreting it. This enables a performance boost in code execution, hugely benefiting Java.
Question 12. How has Java become a platform-independent language?
Answer – The objective of the development of Java was to enable cross-compatibility across multiple platforms, irrespective of the hardware or software running on the end machine. Java achieves platform independency by compiling the code and then converting it into bytecode. And since bytecode is cross-compatible across different embedded systems, Java, in turn, becomes platform-independent. However, to execute bytecode, the end machine must have a Java Runtime Environment (JRE) installed on it.
Question 13. Can we call Java a self-sufficient object-oriented programming language?
Answer – Since everything in Java is under its respective classes which can be accessed by creating objects, it’s not wrong If we call Java an object-oriented programming language. However, we cannot claim that Java is purely an object-oriented programming language as it has direct access to primitive data types like int, float, char, Boolean, double, etc. Therefore, Java is indeed an object-oriented programming language, but not at all a pure OOP language.
Question 14. An integral part of C++ is pointers. Why does Java not utilize pointers?
Answer – C++ being a compiled language hugely benefits from pointers. And since it’s quite a complicated language, in C++, the usage of pointers is unsafe and complex. Java, on the other hand, focuses on code simplicity. However, by not implementing pointers, Java does furnish a certain degree of abstraction. The higher the usage of pointers, the slower the procedure of garbage collection, therefore, Java utilizes references as these cannot be manipulated, unlike pointers.
Question 15. Explain your understanding of an instance variable and a local variable. What are the differences?
Answer – An instance variable is accessed by all methods in the class and is declared outside the methods and inside the class. Such variables describe the properties of an object and will have a copy of a variable. Therefore, any changes will be affected in a particular instance. In contrast, local variables are present within a block or function and can be accessed only inside them. Whenever a local variable is declared, other class methods aren’t updated about it.
Intermediate Java Interview Questions and Answers
Question 16. What is the difference between checked and unchecked exceptions?
Answer – Checked exceptions are exceptions that must be declared in a method or handled using a try-catch block, while unchecked exceptions do not need to be declared or handled.
Question 17. What is the difference between final, final, and finalize?
- final keyword that can be used to show that a variable or method cannot be changed or overridden.
- finally is a block that is guaranteed to be executed regardless of whether an exception is thrown.
- finalize is a method that is called by the garbage collector before an object is destroyed.
Question 18. What is the difference between a HashSet and a TreeSet?
Answer – HashSet is an unordered collection of unique elements, on the other hand TreeSet is a sorted set that maintains elements in ascending order by default.
Question 19. What is the difference between a HashMap and a HashTable?
Answer – HashMap is a non-synchronized collection of key-value pairs, while HashTable is a synchronized collection of key-value pairs.
Question 20. What is the difference between an ArrayList and a LinkedList?
Answer – ArrayList and LinkedList are classes in the Java Collection framework that implement the List interface.
ArrayList in layman’s terms is a resizable array and provides efficient indexing, making it ideal for scenarios where random access to elements is required.
LinkedList is implemented as a doubly linked list and is more efficient than arraylist with frequent additions and removals of node elements.
Therefore, ArrayList is better where random access to elements by index is needed, on the other hand, LinkedList is efficient when frequent additions and removals of node elements are required.
Question 21. What is a thread?
Answer – A thread is a lightweight process that can run concurrently with other threads within a single process.
Question 22. What is synchronization?
Answer – Synchronization is the process of controlling access to shared resources in a multi-threaded environment to prevent race conditions and other concurrency issues.
Question 23. What is the difference between a thread and a process?
Answer – A thread is a lightweight process that exists within a single process, while a process is a separate instance of a program that can contain one or more threads.
Question 24. What is a deadlock?
Answer – A deadlock is a situation in which two or more threads are blocked waiting for each other to release a resource, resulting in a state where none of the threads can proceed.
Question 25. What is the difference between a stack and a queue?
Answer – A stack is a last-in, first-out (LIFO) data structure, while a queue is a first-in, first-out (FIFO) data structure.
Advanced Java Interview Questions and Answers
Question 26. What is reflection?
Answer – Reflection is a feature in Java that allows a program to examine and modify its own structure and behavior at runtime.
Question 27. What is a lambda expression?
Answer – A lambda expression is a way to represent a block of code that can be passed as an argument to a method or stored in a variable.
Question 28. What is a stream?
Answer – A stream is a sequence of elements that can be processed in parallel or sequentially.
Question 29. What is the difference between a stream and a collection?
Answer – A collection is a data structure that stores a finite number of elements, while a stream is a sequence of elements that can be processed in parallel or sequentially without storing them.
Question 30. What is the difference between a functional interface and a regular interface?
Answer – A functional interface is an interface that contains only one abstract method, while a regular interface can contain multiple abstract methods.
Question 31. What is a Java Bean?
Answer – A Java Bean is a Java class that follows a set of conventions to make it reusable and interoperable with other Java components.
Question 32. What is the difference between a heap and a stack?
Answer – A heap is a region of memory used for dynamic memory allocation, while a stack is a region of memory used for storing variables and function calls.
Question 33. What is the difference between an inner class and a nested class?
Answer – An inner class is a class that is defined inside another class and has access to its enclosing class’s members, while a nested class is a class that is defined inside another class but does not have access to its enclosing class’s members.
Question 34. What is the difference between an abstract class and an interface?
Answer – An abstract class can contain both abstract and concrete methods, while an interface can only contain abstract methods. An abstract class can also contain instance variables, while an interface cannot.
Question 35. What is the Java Memory Model?
Answer – The Java Memory Model defines the rules for how Java programs interact with computer memory, including how variables are stored and accessed by multiple threads.
In this article, we quickly revised the top 35 frequently asked JAVA interview questions and answers. Now all the best. May the force be with you 🔥
Understanding the fundamentals, and Java programming questions, as well as having a well-structured answer to every java interview question for freshers can help you nail the selection process for one of the high-paying jobs in the IT industry. However, don’t just limit your depth to only the 15 Java interview questions and answers for freshers we could add and keep on following Geekster Blog for more informative articles from the ever-exciting world of programming.
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