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Core Java Interview Questions and Answers


Core Java is a programming language and also a platform for computing. Core Java was first released by Sun Microsystems in 1995. There are lots of applications and websites that will not work unless Java is installed in them. Each day there are more and more applications created using Java. It is a very simple, powerful and robust programming language which provides a fast, secure, and reliable platform to work on. Java is being used everywhere, from laptops to data centers, game consoles to scientific supercomputers, and cell phones to the Internet.

Due to its ease of use and simplicity, Java is used almost everywhere in the IT sector. This means that the professionals who are skilled in Java are always required. If you are someone who is likely to attend a job interview that would test you on your Java skills, then please go through the list of Java interview questions and answers provided herein. You may also refer to them just to add on to your knowledge, but for dedicated knowledge enhancement, don't forget to check out JanBask’s Java online course.

Core Java Interview Questions and Answers Cover:

  1. Core Java Interview Questions for Freshers
  2. Core Java interview Questions for Experienced
  3. Core Java Interview Questions for Senior Developers

Core Java Interview Questions & Answers for Developers

For a Core Java enthusiast who is looking to attend a Core Java role interview anytime soon, here are the most popular interview questions and answers that might come your way. We have tried to include the top frequently asked Java interview questions as well as their answers to help freshers and experienced professionals with their job interviews. Here are some of the Java interview questions for experienced and freshers.

Q1). Explain the difference between JDK, JRE, and JVM.





JDK stands for Java Development Kit and is the tool used to compile, package and document Java programs.

JRE stands for Java Runtime Environment and is a runtime environment that is a prerequisite to run java byte-code.

JVM stands for Java Virtual Machine and is a specification that facilitates a run-time environment in which Java’s bytecode can be implemented.

Q2). What makes Core Java a platform-independent programming language?

Ans:- Java is platform-independent because it provides the feasibility to run and compile the program in one platform and execute the program on any other platform of your choice.

Q3). Would it be correct to say that Core Java is not 100% Object-oriented?

Ans:- Yes, it would be correct to say that Java is not 100% Object-oriented because it utilizes eight kinds of primitive data types and they are - Boolean, byte, char, int, float, double, long, short. These data types are not objects.

Q4). What is a constructor in Core Java?

Ans:- A constructor is a block of code that is used in a Java environment to initialize an object. It carries the same name that you had given to the class. A Java constructor is automatically called when an object is created.

Q5). Differentiate between a constructor and a method? Can we mark constructors final?

Ans:- A constructor constructs the value, by providing data for the object. It is a special type of method that is used to initialize the object. The constructor has the same name as the class itself, has no return type, and is invoked using the new operator. A method is an ordinary member function of a class. A method can be invoked using the dot operator and has its own name, and a return type. No, declaring the constructor as final is not possible.

Q6). What is a class in Core Java?

Ans:- A class, in the environment of Core Java, are some templates that are used for object creation, and to define certain object data types and their methods.

Q7). State the significance of public, private, protected class.


  • Public: When a class is public, the public class is visible in other packages, the field is visible everywhere.
  • Private: Private variables or methods can be used by an instance of the same class only which declares the variable or method. A private feature can be accessed by the class that owns the feature.
  • Protected: Protected variable is available to all classes in the same package. It is also available to all subclasses of the class that owns the protected feature. Subclasses that reside in a different package also are provided with access from the class that owns the protected feature.

Q8). What is the final class?

Ans:- A final class is a constant value of a final variable. Extending A final class is not possible ie., final class may not be subclassed. A final method cannot be overridden when its class is inherited.

Q9). What is a wrapper class?

Ans:- The classes that “wrap” the primitive data type into an object of that class are called wrapper classes.

Core Java interview Questions for Experienced

Here are the Core Java interview questions and answers for experienced professionals who have gained some experience and are looking to upgrade their career.

Q10). What is an abstract class?

Ans:- Abstract serves as a template. In order to use an abstract class, it must be extended or subclassed. An abstract class may not be instantiated. Any class with an abstract method is abstract itself, hence is declared as such.

Q11). Describe synchronization with respect to multithreading.

Ans:- Synchronization is the method to control the access of multiple threads to shared resources, with respect to multithreading. One thread can modify a shared variable when not in synchronization even when another thread is in the process of using or updating the same shared variable. This can lead to significant errors, which you shall learn more about as you proceed towards advanced java programming.

Q12). What is the purpose of garbage collection in Core Java, and when is it used?

Ans:- The main purpose of garbage collection is to analyze a program, identify and discard the objects that are no longer needed. It is helpful as the resources can be reclaimed and reused. A Core Java object is subjected to garbage collection when the object is not reachable to the program in which it is used.

Q13). What are the different ways of implementing thread? Which one is more advantageous?

Ans:- The thread can be implemented by using runnable interface Inheriting from the Thread class. The use of the Runnable interface is more advantageous because when going for multiple inheritances, the only interface can help.

Q14). What if the main() method is declared as private? What happens when the static modifier is removed from the signature of the main() method?

Ans:- When the main() method is declared as private, the program compiles but during runtime it shows “main() method not public.” Message. When the static modifier is removed from the signature of the main() method, the Program compiles but at runtime throws an error “NoSuchMethodError”.

Q15). What is the first argument of the String array in the main() method?

Ans:- Unlike in C/C++ where the first element by default is the program name, the string array in main() has no element, the String array is empty. When you enter the wave of coding, you shall notice such differences.

Q16). What is a Core Java servlet?

Ans:- A Servlet in Core Java refers to the server-side technologies which are used to extend the competence of web servers by giving it support for a dynamic response as well as data persistence.

Q17). The Life-cycle of a Core Java Servlet.

Ans:- Here is the life-cycle of a Core Java Servlet-

  • Servlet is loaded
  • Servlet is instantiated
  • Servlet is destroyed
  • Servlet is initialized
  • Service the request

Q18). Explain the Request Dispatcher?

Ans:- Request Dispatcher is a Core Java interface that is used to forward a request to some other resource which can be HTML, JSP or any other Core Java servlet within the same application.

Q19). List the steps to connect to a database in Core java?

Ans:- Follow the given steps to connect to a database in Core java-

  • Close the Connection
  • Register the Drive Class
  • Create Connection
  • Create Statement
  • Execute Queries

Q20). What do you mean by a JDBC Driver?

Ans:-  JDBC Driver in Java refers to a software component that allows Java applications to relate with the database.

There are 4 types of JDBC drivers in Java-

  • JDBC-ODBC bridge driver
  • Native-API driver (partially java driver)
  • Network Protocol driver (fully java driver)
  • Thin driver (fully java driver)

Q21). What’s the use of the transient keyword in Core Java?

Ans: Java interview questions like this may appear difficult, but the concept is simple. The transient keyword in Java is a field modifier used to indicate that a field should not be included when the object is serialized into a byte stream. Fields marked as transient are excluded from the persistent storage and are particularly useful when certain fields contain sensitive or unnecessary data that don’t need to be saved during serialization. This ensures data privacy and reduces unnecessary storage.

Q22). What is method overloading in Core Java?

Ans: Basic Java interview questions like this one are a must-know for beginner developers who might want to try out Polymorphism. Method overloading in Java allows programmers to define two or more methods within the same class sharing the same name, as long as their parameter lists are different. This makes it easy for Java interview questions for freshers to expand APIs, improving code usability by allowing multiple ways to call a method with different argument combinations. The expansion to the JLS has a more detailed explanation.

Q23). What is method overriding in Core Java?

Ans: When discussing basic Java interview questions, it's particularly important to understand method overriding in Java. It occurs when a subclass provides a specific implementation for a method that is already defined in its superclass. This allows the subclass to customize or extend the behavior of the inherited method. When the overridden method is called on an instance of the subclass, the subclass's implementation is executed instead of its superclass's.

Q24). In Core Java, what is the == operator used for when comparing objects?

Ans: Questions in Core Java viva questions may involve operator usage. In Java, the == operator is used for reference comparison. It checks whether two object references point to the same memory location. On the other hand, the .equals() method, when overridden by a class, compares the content or value of objects based on the class's implementation. This allows for custom comparison logic.

Q25). In Core Java the try-with-resources statement is used in Core Java interview questions experienced. Describe the concept of this statement.

Ans: In Core Java interview questions experienced, the try-with-resources statement is significant. It is used to automatically manage and close resources that need explicit closure, such as files, sockets, or database connections. It simplifies resource management and reduces the risk of resource leaks and exceptions. The resources declared within the try-with-resources block are automatically closed when the block exits.

Q26). What is method chaining in Core Java?

Ans: Design patterns might be explored in interview questions on Java. Method chaining in Core Java is a design pattern where multiple methods are called on an object in a single line, with each method returning the modified object. This pattern provides a way to produce code that is readable and concise since methods can be called in a chain, avoiding the need for intermediate variables.

Q27). How does Core Java support multiple inheritance?

Ans: When answering Java basic interview questions, it's vital to mention multiple inheritance. Core Java supports multiple inheritance using interfaces. A class can implement multiple interfaces, allowing it to inherit method signatures (a.k.a., contractual obligations) from multiple sources. This helps evade class inheritance’s associated ambiguity and complexities, since a class can only inherit from one superclass.

Q28). What is the purpose of the volatile keyword in Core Java?

Ans: Core Java interview questions and answers often delve into synchronization. In Core Java, the volatile keyword is used to declare a variable as volatile, ensuring that read and write operations of the variable are atomic and immediately visible to all threads. It prohibits individual threads from caching the variable’s value, making it a good fit for variables accessed concurrently by multiple threads.

Q29). Differentiate between the ArrayList and LinkedList in Core Java?

Ans: Core Java interview questions often involve data structures in Java. The ArrayList and LinkedList both store collections of objects, but they have different underlying data structures and characteristics. The ArrayList is backed by an array, so it’s efficient for random access (get and set operations), but less so for insertions and deletions in the middle of the list. The LinkedList is implemented as a doubly-linked list, so it’s efficient for insertions and deletions in the middle of the list, but less so for random access.

Q30). What is the hashCode() method used for in Core Java?

Ans: Core Java interview questions like these are important for any Core Java developer. The hashCode() method in Core Java is used to calculate a hash code value for an object, which is used by data structures like HashSet and HashMap to store and retrieve objects. The default implementation in the Object class returns the memory address of the object in an integer format, but classes can override the method to provide custom hash code implementation.

Q31). Explain Reflection in Core Java, its uses and why it’s important?

Ans: Reflection in Core Java is a powerful and advanced feature that allows you to inspect and manipulate classes at runtime even though classes (fields,methods,constructors etc.) are not identified at compile time. The ability to reflect on the code is pivotal for several advanced applications, running frameworks and tools which require to “get information about followed analysis and execution of methods”.

Q32). What is the difference between Comparable and Comparator interfaces in Core Java?

Ans: The Comparable interface is used for objects of each class that need to be ordered with a single logical ordering, through the use of the compareTo method. By contrast, the Comparator interface is used to define multiple possible orderings for objects by external implementations of the methods, allowing for the flexibility of custom ordering to be provided without modifying the actual class of the object. These concepts forms a critical part of a Core

Java online course that focuses on the data structures, particularly that of sorting algorithms.

Q33). Explain the importance of Generics in Core Java.

Ans: Generics provide a much broader definition of objects than the Object class, which thereby permits a much broader range of functions to be performed on the data. By adding stability to the code, it will make more of programmers' bugs become discoverable at the compile time, rather than the execution time. The programmer may possibly, with a single method declaration, specify a set of related methods; with a single class declaration, specify with a set of related types. 

Q34).  How do you handle exceptions in Core Java?

Ans: Exception handling in Core Java is managed through the use of try, catch, finally blocks, and the throws keyword. The try block encloses the code that might throw an exception, while the catch block is used to handle the exception. The finally block contains code that is always executed after the try and catch blocks, regardless of whether an exception was thrown or caught. The throws keyword is used in method signatures to indicate that a method might throw one or more exceptions. Proper exception handling is crucial for building robust Java applications and is a common focus in both Core Java learning online platforms and Core Java courses.

Q35). What are the different types of memory areas for JVM?

Ans: JVM is divided into following types of memory areas:

a) Heap

b) Stack

c) Method Area

d) Program Counter (PC) Register

e) Native Method Stack

Heap – This is used for dynamic memory allocation for all the objects and JRE classes.

Stack – For every thread, there is one runtime stack which is created. This is used in a method to store local variables when defining a method.

Method Area – This one stores per-class structures such as the run-time constant pool, field and method data, and the code for methods.

Program Counter (PC) Register – Core Java Virtual Machine instruction uses this register.

Native Method Stack – To execute a native method this stack is used.

To optimize the Core application’s performance, you need to understand these areas very well and this is covered in Java interview questions for experienced professionals of our Java courses. 

Q36). Explain the difference between fail-fast and fail-safe iterators in Core Java.

Ans: Fail-fast iterators immediately throw a ConcurrentModificationException if there is a structural modification of the collection while iterating over it except through the iterator’s own remove method. Fail-safe iterators don’t throw any exceptions if a collection is structurally modified while iterating over it because they work on a clone of the collection, not on the original collection itself. This is one of the most important and frequently asked questions in Core Java core interviews. This is generally asked in Core Java online courses at the basic level also.

Q37). What is the Double-Checked Locking idiom in Core Java concurrency?

Ans: The Double-Checked Locking idiom reduces the overhead of acquiring a lock by first testing the locking criterion (the lock is actually acquired for real if the locking criterion indicates the lock’s presence). This idiom is often used for lazily initializing the singleton object. It must be implemented with care in Core Java to be thread-safe. Generally it is implemented using volatile variables. It is an advanced concurrency pattern and covered in detail in many of the Core  Java training programs which focuses on design patterns and concurrency.

Q38). Discuss enhancements in Core Java 9 Module System.

Ans: The Core Java 9 Module System (Project Jigsaw) introduces a modular approach to Java application development. Modules make it easier for developers to organize their applications, with explicit dependencies where a module can explicitly declare itself to depend on specific other modules. This approach to scalability — turning the company’s myriad of Core Java projects into modules — is much more practical than creating a giant monolithic application. Modules make it easier to manage and turn large applications into a few much smaller applications where the only pieces of a framework that are used are the pieces actually required. This is one of the more significant topics in Core Java learning online because it significantly changes the way Core Java applications are organized and so should be designed and developed for much better organization and much improved runtime performance.

Q39). How do you use the default keyword in Core Java interfaces?

Ans: The default keyword in Core Java interfaces enables developers to provide method implementations directly within the body of the interface. This feature, introduced in Java 8, effectively allows interfaces to be extended without having to revise every implementing class. The benefit of this is that it permits developers to expand large codebases of interfaces without fear of breaking the old code. Default methods are a common topic of interest in Core Java courses and Core Java training, as they provide a new sense of flexibility and extensibility to what has always been a rigid outline of APIs.

Q40). What are some benefits of the Stream API in Core Java for parallel operations?

Ans: The Core Java Stream API gives developers a way to process viewless collections of objects in a functional manner. The primary advantage of using the Stream API is the ease with which it can be parallelized, allowing for significant performance improvements in a multi-core system. By employing the parallelStream method, the developer can effortlessly transition between sequential and parallel execution modes without modifying the original code structure; the simple act of changing the method call makes the Stream API an effective tool for efficiently handling complex data processing, a theme that is emphasized in Core Java online courses which focus on performance optimization.

Q41).  What is type erasure in Core Java Generics? 

Ans: Type erasure is a process that is applied by the Core Java compiler in order to apply type constraints at compile time and then remove the generic type information replacing it with non-generic upper bounds (such as Object) and raw types. This means that the information that a generic type used is not available at runtime. The process was introduced to ensure binary backward compatibility with pre-existing versions of Core Java that did not have generics.

Q42). Discuss the importance of volatile keyword in Core Java’s memory model.

Ans: The volatile keyword in Core Java is used to ensure visibility of changes to variables across threads. When a variable is declared volatile, any write to that variable is immediately made visible to other threads. This prevents threads from caching the variables value, ensuring that each pthread has the most up-to-date value of a variable. It's important in concurrent programming as it helps avoid inconsistent states and is a fundamental concept covered in a Core Java course, particularly as it pertains to Core Java’s memory model and how volatile variables impact thread communication.

Q43). Explain Core Java Memory Leaks and how to avoid them?

Ans: Core Java memory leaks occur when objects are no longer being used, but cannot be garbage collected because they are still being referenced. Over time, memory leaks can result in an application using an excessive amount of memory, causing performance degradation or crashes. Avoiding memory leaks involves being careful about how long a reference to an object is held, using weak references where appropriate, and always dereferencing an object when it’s no longer needed. 

Q44). What is the role of the @FunctionalInterface annotation in Core Java?

Ans: The @FunctionalInterface annotation in Core Java is used to indicate that an interface type declaration is intended to be a functional interface, as defined by the Core Java Language Specification. Function interfaces have exactly one abstract method. This is not required, but helps the compiler to understand the intention of the interface. That being said, this area is found to be usually heavily covered in a modern Core Java course, especially those introducing Lambda expressions or Core Java programming with regard to functional programming.

Q45).  What is the purpose of the @Override annotation in Core Java?

Ans: The @Override is used in Core Java to indicate that a method you are overriding is intended to actually be an override. That way you can be sure if you’re reading the code of the overriding method because the IDE and compiler can tell you for sure through the presence of the @Override annotation. This will allow for checking errors like misspelling the method name or not correctly matching the method signature, so the programmer can let the compiler find the error.

Q46). How can you achieve thread-safe singleton in Core Java?

Ans: To achieve thread-safe singleton in Core Java, you can use Bill Pugh Singleton implementation or an enum based singleton. Bill Pugh uses a static inner helper class to hold the singleton instance, creating it only when requested and leveraging Core Java's class loading mechanism for thread safety. Enum based singleton ensures a single instance is created through Core Java's guarantee that any enum constant is instantiated only once in a Core Java program. These design patterns are fundamental to application efficiency and scalability, integral topics in advanced Core Java training.

Q47). Explain differences between Checked and Unchecked exceptions in Core Java.

Ans: Checked exceptions are checked by the compiler to ensure they are caught or declared in the method's throws clause, aiding in notifying the developer of error scenarios that may arise while the code is being written. Unchecked exceptions are often the result of programming defects and are usually not recoverable, breaking the normal flow of the application. They do not require to be declared on a method's throws clause. A strong understanding of this distinction, and proper usage, is expected; and can be reinforced through reinforcement of key concepts while you go through Core Java online course.

Q48). What is the Diamond Problem in Core Java and how does Core Java address it?

Ans: The Diamond Problem is a multiple inheritance problem that occurs when a class tries to inherit from two classes that have a method with the same signature. Core Java addresses this issue via interfaces, rather than by allowing multiple inheritance of classes. With default methods in interfaces, if a class implements two interfaces that have a default method with the same signature, the class is required to override the method to resolve the ambiguity. This is an important part of the Core Java online course curriculum for beginners, as it illustrates how Core Java deals with object-oriented design.

Q49). How do you use the assert keyword in Core Java and when is it appropriate?

Ans: The assert keyword in Core Java is used for debugging, to test assumptions about the state of a program. An assertion will throw an AssertionError if the specified condition is false. Assertions are typically used during development and in testing to find and fix errors early in the life cycle. However, it is best practice to handle exceptions for error handling in production code. The use of assertions is a subject that is covered in detail in Core Java courses as developers learn to debug their applications effectively.

Q50). Explain the concept of method references in Core Java 8.

Ans: Method references in Core Java 8 are shorthand notations for lambda expressions that call existing methods. With method references, you can make your code more readable and concise by eliminating the need to include boilerplate code that just calls a method without modifying its arguments. Method references refer to static methods, instance methods of a specific object, constructors, or instance methods of an arbitrary object of a particular type. 

Q51). Discuss the role of transient and volatile keywords in Core Java serialization.

Ans: In Core Java, the transient keyword prevents fields from being serialized. This protects sensitive or otherwise useless data from being serialized along with the rest of an object. The volatile keyword does not directly affect serialization, but it dictates that all threads running read the variable at the same time. In other words, volatile is used to ensure that any change to a variable is picked up by other threads immediately, making it important when using shared variables in a multi-threaded application. Both of these concepts are important to understand, and both feature heavily in a proper Core Java learning online course.

Q52). What is the NavigableSet interface in Core Java?

Ans: The NavigableSet interface extends the SortedSet interface to provide navigation methods for retrieving elements based on their position in the set. You can, for example, retrieve elements greater than or equal to, less than or equal to, or within a certain range. This interface is a particularly powerful way to work with ordered sets of data. 

Q53). How does the forEach method in Core Java 8 enhance collection processing?

Ans: The forEach method, added in Core Java 8, gives a new, much improved way, to iterating collections using lambda expressions or method references. This provides a more readable, and concise way to iterate the elements of a collection. forEach is defined in the Iterable interface so that you can perform a sequence of elements on every Collection. As a result this new method gives a way to do functional-style operations on every element of a collection. 

Q54). How do you differentiate between `static` and `instance` methods in Core Java?

Ans: In Core Java, `static` methods belong to the class itself and can be called without creating an instance of the class. They can only access static data members and other static methods. Instance methods, on the other hand, require an object of the class to be created and can access both instance and static data members and methods. This distinction is critical for understanding object-oriented programming principles in Core Java, a common area of focus in core java interview questions.

Q55). What is the significance of the `interface` keyword in Core Java?

Ans: The `interface` keyword in Core Java is used to define an abstract type that specifies a set of method signatures without providing their implementations. Classes can implement interfaces, thereby agreeing to provide implementations for the abstract methods declared within them. Interfaces support multiple inheritances in Core Java and are a cornerstone of Java's approach to polymorphism and abstraction, topics frequently covered in java interview questions for freshers.

Q56). Explain the use of the `super` keyword in Core Java

Ans: The `super` keyword in Core Java is used within a subclass to refer to the superclass's variables, methods, and constructors. It is particularly useful for accessing and invoking the superclass's constructor methods, overriding methods, or when the names of global variables are hidden by local variables. Understanding `super` is fundamental for mastering Java's inheritance features, making it a popular topic in basic Core java interview questions.

Q57). Can you modify the value of a final variable in Core Java?

Ans: In Core Java, a `final` variable can only be assigned once, either at the time of declaration or within the constructor. Once assigned, its value cannot be modified, making it effectively a constant. This immutability concept is critical for creating secure, thread-safe code, and is a concept that is often tested in Core Java viva questions.

Q58). What are Core Java Packages and how do you use them?

Ans: Core Java packages are used to group related classes and interfaces, providing a controlled namespace mechanism that helps avoid name clashes. Packages can be imported into other Core Java files, allowing the classes and interfaces they contain to be easily reused. Understanding how to create and use packages is a basic yet essential part of Java programming, often discussed in core java interview questions.

Q59). Describe the role of the `public static void main(String[] args)` method in Core Java.

 Ans: The `public static void main(String[] args)` method is the entry point for a Core Java application. The `public` modifier makes it accessible from outside its class, `static` allows it to be invoked without creating an instance of its class, `void` indicates it doesn't return any value, and `String[] args` is an array that stores command-line arguments. This method's understanding is essential for all Core Java developers, making it a staple in Core Java interview questions.

Q60). How does the `try-catch-finally` block work in Core Java?

Ans: In Core Java, `try-catch-finally` blocks are used for exception handling. Code that might throw an exception is placed in the `try` block. The `catch` block is used to handle the exception, and the `finally` block contains code that is executed after the `try` and `catch` blocks, regardless of whether an exception was thrown or caught. The `finally` block is typically used for resource cleanup activities. This concept is foundational for robust Core Java application development, frequently explored in Core Java interview questions for freshers.

Q61). What is the difference between `==` and `.equals()` in Core Java?

Ans: In Core Java, `==` is a reference comparison operator that compares whether two references point to the same object in memory. In contrast, the `.equals()` method is intended for content comparison, checking if two objects have the same value. Not all classes override `.equals()`, so its behavior can vary unless specifically implemented. This distinction is crucial for understanding Core Java's comparison mechanisms, a common subject of basic Core java interview questions.

Q62). Explain garbage collection in Core Java.

Ans: Garbage collection in Core Java is an automatic memory management process that frees up memory allocated to objects that are no longer in use, preventing memory leaks. The garbage collector determines which objects are not referenced by any running state or other objects and removes them to free up space. While developers do not control the garbage collection process directly, understanding its workings is important for optimizing application performance, a topic often included in Core Java viva questions.

Q63). What are wrapper classes in Core Java?

Ans: Wrapper classes in Core Java provide a way to use primitive data types (int, char, etc.) as objects. The eight primitive data types have corresponding wrapper classes in the `java.lang` package (e.g., `Integer` for `int`, `Character` for `char`, etc.). These classes are essential for working with collections, which can only store objects. Understanding wrapper classes is fundamental for working with Core Java's object-oriented features, often covered in core java interview questions.

Core Java Interview Questions For Senior Developers & Core Java Interview Questions For 5 Years Experience

Here are the top Java interview questions and answers for experienced senior developers you should study.

Q64). What is a Core Java applet?

Ans:- The applet is a Core Java program that is designed for transmitting the Core Java code over the internet. Ttion works automatically by Java-enabled Web Browser. The applet can respond to the user input immediately as it is dynamically programmed.

Q65). What is numeric promotion?

Ans:- Numeric promotions of a numeric operator are used for the conversion of the operands into a common type. In order to perform calculations easily, numeric promotion, conversion is performed. It is the conversion of a smaller numeric type to a larger numeric type so that integer and floating-point operations can be performed over it. Here byte, char, and short values are converted to int values. The int values are converted to long values, and the long and float values are converted to double values.

Q66). What is false sharing in the context of multi-threading?

Ans:- On multi-core systems, false sharing is one of the well-known performance issues. Here each process has its local cache. When threads on a different processor, modify variables false sharing occurs, that resides on the same cache line as shown in the following images

As the thread may access different global variables completely, false sharing can be hard to detect. Finding this interesting? Well knowing everything about Java is essential, but the actual truth is, that you can never be a master, and there shall always be scope to learn more Java developer skills.

Q67). What are the methods used to implement the key Object in HashMap?

Ans:- Equals and hashcode methods are to be implemented In order to use any object as Key in HashMap, in Java.

Q68). What is an immutable object?

Ans:- Core Java classes whose objects cannot be modified once they are created are known as Immutable classes. Any modification of Immutable object results formation of the new object.

Q69). Differentiate between StringBuffer and StringBuilder in Core Java?

Ans:- The only difference between StringBuffer and StringBuilder is that StringBuffer methods are synchronized while StringBuilder is not synchronized. StringBuilder in Java was introduced in Java 5.

Q70). What is the difference between a factory and abstract factory patterns?

Ans:- Abstract Factory provides one more level of abstraction. Consider different factories each extended from an Abstract Factory and responsible for the creation of different hierarchies of objects based on the type of factory. E.g. Abstract Factory extended by Automobile Factory, User Factory, Role Factory, etc. Each individual factory would be responsible for the creation of objects in that genre.

Q71). Differentiate JAR and WAR files

Ans:- We are going to share the Difference between the JAR & WAR File:



Full form of JAR files is Java Archive Files.

Full form of WAR files is Web Archive Files.

Aggregating many files into one is allowed in JAR files

XML, Java classes, and JavaServer Pages are stored in WAR

The JAR is usually used to hold Java classes in a library.

Mainly used for Web Application purposes.`  

Q72). What is a JIT compiler?

Ans:- Just-In-Time(JIT) compiler is used to improve the performance. JIT compiles parts of the bytecode that has similar functionality which in turn reduces the amount of time needed for compilation. The term “compiler” here refers to a translator from the instruction set of a Core Java virtual machine (JVM) to the instruction set of a specific CPU. It's essential to know how long it shall take to learn Java, so you know on which Core Java basic interview questions to focus more.

Q73). What is the multi-catch block in Core Java?

Ans:- Multi-catch blocks make the code shorter and cleaner when every catch block has a similar code. We can catch multiple exceptions in a single catch block using this feature.

Q74). What is a package in Core Java? 

Ans:- The collection of related classes and interfaces grouped together is Package in Core Java. It enables developers to easily modularize codes. Packages help in providing easier access control on the code.

Q75). What is the final keyword in Core Java?

Ans:- Final is a special keyword in Core Java being used as a non-access modifier. It is used in various contexts like Final variables, Final Methods, and Final Class. Final class refers to a class being declared as final in Core Java. 

Q76). What are the various types of inheritance in Core Java?

Ans:-  Core Java has four types of inheritance namely:

  • Single inheritance - Herein one class inherits the properties of another class.
  • Multilevel inheritance - A class having more than one parent class but at different levels is termed as Multilevel inheritance.
  • Hierarchical inheritance - When a class has more than one child class it is termed as hierarchical inheritance.
  • Hybrid inheritance - It’s a combination of two or more types of inheritance.

Q77). What is the most important feature of Core Java8?

Ans:- The most important feature of Core Java 8 is its functional interface and static methods. When adding a functional interface to the object-oriented interface, programming becomes less complicated and more efficient. To know about the more Core Java 8 important features, you can opt for Java projects for beginners, and understand better through practical approach.

Q78). What is the difference between path and classpath variables?

Ans:- Classpath is related to Core Java executables, used to locate class files. Path, on the other hand, exists in an operating system used to locate executables.

Q79). Can you explain serialization and deserialization?

Ans:- Both serialization and deserialization are crucial to stream handling in Core Java. Through serialization, you convert an object into a byte stream, and through deserialization, you simply undo the process.

Q80). What is a ternary operator?

Ans:- A ternary operator is a conditional operator in Core Java used to decide what values to be assigned to a variable.

Q81). What is platform independence?

Ans:- Platform independence is when you design a program that runs on any operating system making things more accessible. This is the reason why Java is ahead of other programming languages.

Q82). Which is the latest Core Java release?

Ans:- As of Sep 2023, Java 21 is the latest release. Also, it is the next long-term support version (LTS) after Core Java 11.

These are some of the most asked interview questions you should prepare for your next Core Java Interview. Read our next section for the most essential interview tips.

Q83). What are the differences between C++ and Core Java?

Ans:- C++ is not platform-independent; the main concept behind it, “write once, compile anywhere.”  Since the byte code generated by the Core Java compiler is platform-independent, it can run on any machine, Java programs are written once and run everywhere.

Most of the high-level languages are compatible with C++ but with Java they are incompatible.

Q84). List the features of the Core Java Programming language?

Ans:- Some of the significant features of Core Java Programming Language are:

  • Core Java is an easy-to-learn language. The Fundamental Concept of OOP Java has a catch to understand. 
  • The secured feature of Core Java helps develop a virus-free and tamper-free system for the users.
  • It is an OOP or Object-Oriented Programming language. OOP signifies that everything is considered an object in this language.
  • This programming language is not compiled into a platform-specific machine; instead, it is compiled into platform-independent bytecode.

Q85). What makes a HashSet different from a TreeSet?

Ans:- Here is the difference:

1. HashSet:  It is implemented through a hash table and permits the null object. 

TreeSet:  implements SortedSet Interface that uses trees for storing data. 

2. HashSet: It permits the null object.

TreeSet: It does not allow null objects.  

3. HashSet:  It does not maintain elements in an ordered way.  

TreeSet: It maintains elements in a sorted way.  

Q86). What is a package in Core Java? List down its major advantages.

Ans:- It is a collection of related classes and interfaces which are bundled together. It allows developers to easily modularize the code and optimize its reuse. Also, the code within the packages can be imported by other classes and reused.

  • Packages are helpful in avoiding name clashes 
  • They provide easier access control on the code 
  • They can also carry hidden classes that are not visible to the outer classes 

Q87). What is the importance of reflection in Core Java?

Ans:- It is a runtime API used to inspect and change the behavior of methods, classes, and interfaces. Core Java Reflection is a powerful tool that allows you to analyze classes, interfaces, fields, and methods during runtime without knowing what they are called at compile time. It also helps in creating new objects, call methods, and getting/set field values. 

Q88). What is Core Java String Pool?

Ans:- A collection of Strings stored in heap memory is called Core Java String Pool. Whenever a new object is formed, first of all, the String pool identifies whether the object is already present in the pool or not. If it is present, then the same reference is returned to the variable; otherwise, a new object is created.

Q89). What is a Map in Core Java? 

Ans:- A map in Java is an interface of the Util package that maps unique keys to values. The Map interface is not a subset of the main Collection interface and hence it performs a little differently from the other collection types.

Q90).  Why is Inheritance used in Core Java?

Ans:- Inheritance in Core Java allows for the reuse of code

  • Without using inheritance, runtime polymorphism cannot be achieved
  • It also provides data hiding
  • Method overriding is not possible without inheritance. 

Q91). Why is Core Java dynamic? 

Ans:- Java is dynamic in nature, it is designed to adapt to an evolving environment. It includes a large amount of runtime information that is used to solve access to objects in real-time.

Q92). What is a JSP page? 

Ans:- JSP stands for Java Servlet Page. The JSP page contains two types of text- Static Data and JSP elements.

Q93). What is the difference between systems.out, System. err, and System. in?  

Ans:- System. out and System. err both represent the monitor by default and so you can use both to send data to the monitor. 

System. out is used to display normal messages and results, System.eerr for error messages, and represents InputStream object which by default represents standard input device, i.e., keyboard.

Q94). Explain the different authentications in Core Java Servlets.

Ans:- These are the four different options for authentication in servlet: 

  • Basic Authentication: For basic authentication, the client provides usernames and passwords to authenticate the user. 
  • Form-based authentication: In this, the login form is made by the programmer by using HTML. 
  • Digest Authentication: It is like basic authentication, the only difference is that here the passwords are encrypted using the Hash formula to make it more secure. 
  • Client certificate Authentication: For client certificate authentication, it needs that each client accessing the resource has a certificate that it sends to authenticate itself. 

Q95). Explain the concept of object-oriented programming (OOP) principles in Core Java.

Ans. Interview questions on Core Java often explore OOP principles. Object-oriented programming in Java is based on four main principles: encapsulation (hiding data and providing access methods), inheritance (reusing and extending classes), polymorphism (multiple forms of a class), and abstraction (representing real-world entities as objects). These principles promote code organization, modularity, and flexibility.

Q96). What is the purpose of the finalize() method in Core Java?

Ans. In basic Core Java interview questions, understanding the finalize() method is important. The finalize() method is a method provided by the Object class, which can be overridden by a class to perform cleanup operations before the object is garbage collected. However, it's not recommended for critical resource management due to uncertainty about when it will be called.

Q97). What is a lambda expression in Core Java?

Ans. Lambda expressions are a new and important feature included in Core Java SE 8. A lambda expression is a concise way to represent an anonymous function. It does not have a name; it is used in functional programming; and it can be passed as a parameter to a functional interface like Runnable or Comparator.

Q98). Explain the concept of object cloning in Core Java

Ans. If you are currently taking a Java course, you may want to learn about object cloning, which is an advanced topic in this area. Object cloning refers to the process of creating an exact copy (clone) of an existing object. It can be accomplished by implementing the Cloneable interface and by providing a custom clone() method. Cloning allows you to create independent copies of objects and is useful when you need to preserve the state of an object. However, cloning must be done carefully to maintain data integrity.

Q99). How does the static keyword affect memory management in Core Java?

Ans. The static keyword in Java indicates that a specific field or method is a class field. With no objects necessary you can call them. A static field or method is created once, and is shared among all instances of the class. It can contribute to effective memory management in large applications, particularly in the context of Java learning online, where static fields can improve manageability. They are used judiciously as they promote reusability and avoid redundancy of instance variables and instance methods.

Q100). Explain the Singleton design pattern in Core Java.

Ans. Singleton design pattern in Java ensures that a class has just one instance and provides a global point of access to that instance. It is used in scenarios like a single database connection shared by multiple objects, and is usually used in scenarios like a single database connection shared by multiple objects in the pool. To implement a Singleton pattern in Java, you should make its constructor private, disable cloning and copying and create a static variable to hold the instance, and create a static method to get and maintain a global access. Singleton design pattern is one of the fundamental concepts in many Java design patterns and really helps to build efficient Java applications, which can be easily maintained and scaled.

Q101). What are the benefits of using Stream API in Core Java 8 for data processing?

Ans. The Stream API introduced in Java 8 is a major advancement in the Java programming language, enabling more expressive and, perhaps more importantly, more efficient data processing. Streams represent a new abstraction on collections, supporting a more expressive and declarative approach to collections processing (including support of operations like filter, map, reduce, and collect). This allows developers to write more readable and more concise code for common operations that involve collections. For this reason, Stream API tends to be the focus of many articles, blogs, and Java training courses for advanced Java learning online. In addition to promoting the functional programming principles of Java, it can offer significant performance improvements to Java applications through parallelization of operations on collections.

Q102). Discuss the role of the Optional class in Core Java.

Ans. The Optional class was introduced in Java 8 and is a container object that is used to contain not-null objects. Optional is a great way of avoiding NullPointerException and it has a lot of other useful methods to help in handling different situations such as 'isPresent()', 'ifPresent()', and 'orElse()' that simplifies the code and prevents the application from breaking. This is also one of the main topics of Java training or Java online course and you should explore more to learn it.

Q103). How do you manage memory leaks in Core Java applications?

Ans. Memory leaks in Java can be managed by ensuring that objects are no longer referenced when they need to be. You might use tools such as 'jmap', 'jhat', 'jstack', and 'jconsole' to identify objects that are not being garbage collected. As these objects do not show up in the heap finder, these tools can be very useful to find where possible memory leaks are within the Java application. Also object finalization in Java can be used to remove unnecessary object references. other techniques involve using a profiler and writing efficient code; using a weak reference can also be handy. Also remember that class loader is a potential source of memory leaks in J2EE. You can explore more with Java online courses. And it is definitely one of the favorite Java interview questions.

Q104). What is the difference between ExecutorService and Fork/Join Framework in Core Java?

Ans. The ExecutorService is a framework provided by the Java concurrency API that simplifies the execution of tasks in asynchronous mode. It provides a pool of threads for executing Runnable and Callable tasks. On the other hand, the Fork/Join Framework, introduced in Java 7, is designed to efficiently handle a large number of tasks. It uses the divide-and-conquer strategy in which a task keeps on dividing itself into further sub-tasks until it is a manageable size and your most important work to be done is done primarily on merging the no of sub-tasks. This approach suits the problems that can be broken down into smaller tasks that can be executed concurrently.

In general ExecutorService is more general with the motive to solve all general problems. While the Fork/Join acts as specialization of ExecutorService, that is designed to handle eval if the tasks can be recursively divided in smaller sub-tasks and then executed, and hence why would it not take advantage of it to provide the performance benefits. You will find these concepts in detail in a Java online course focused on Concurrency and Parallelism.

Q105). What is the significance of the volatile keyword in ensuring visibility of changes across threads in Core Java?

Ans. The volatile keyword in Java is used as an indicator to tell the JVM that a variable will be modified by different threads. The value of this variable will never be cached in a register and all writes to this variable will be written back to the main memory immediately. Understanding volatile keyword is critical for core Java interviews and can be a tough nut to crack, especially the concept of memory visibility and instruction reordering. Similarly experienced Java developer would also be aware of the volatile keyword for preventing compiler optimization and reorder of instruction.

Q106). How do you ensure thread safety in Core Java collections?

Ans. Ensuring thread safety in Java collections is achieved typically through several approaches. One common way is to use the synchronized wrappers provided by the Collections class, such as Collections.synchronizedList() or Collections.synchronizedMap(). Java also provides specific thread-safe collections such as ConcurrentHashMap, CopyOnWriteArrayList, and BlockingQueue. These classes are designed to allow concurrent access and modifications without the need for external synchronization, and are covered in many Advanced Java training courses, pointing out their usage patterns and performance characteristics.

Q107). Explain the impact of Core Java's garbage collection on application performance.

Ans. Java uses garbage collection (GC) as a way to track memory leaks and free up memory that is no longer accessible by your application objects. While this is a good thing, GC can also impact the performance of your Java application, especially during GC pause times. To optimize the performance of Java applications, a developer would look at tuning the GC configuration, selecting different GC algorithms, and minimizing the creation of objects that are unnecessary. Advanced Java training typically covers GC behavior and GC optimization techniques so developers can handle the potential performance issues that can occur.

Q108). Discuss the use of annotations in Core Java.

Ans. Annotations provide a way to add metadata to Java code. This metadata can then be analyzed by the compiler, development tools, or even runtime libraries. They can be used to specify compile-time instructions to the compiler, they can specify runtime processing, and more. The end result is that you can add this information directly to your code and you don't need to maintain it in external configuration files, resulting in a codebase that is cleaner and easier to maintain. Annotations are a covered topic in our Java online course and are a powerful tool for framework developers and can be utilized to reduce the amount of “boilerplate” code that is written, as well as help developers to understand the intention of code.

Q109). What is difference between interface and abstract class?

Ans. Key differences between interface and abstract class are:

  • Interface has only method declarations while abstract class can have complete methods
  • A class can extend only one abstract class but implement multiple interfaces
  • Interface members are public by default unlike abstract classes
  • Interfaces lack constructors while abstract classes can have constructors

Q110). What is ThreadLocal class in Core Java? What common usecases is it helpful for?

Ans. ThreadLocal class allows creating thread local variables to store state isolated from other threads. Some usages are:

  • Uniquely identify user contexts
  • Transaction identity mappings
  • User session identifications
  • Avoid synchronized blocks
  • Database connection objects

Thread safety gets achieved without explicit synchronization.

Q111). Explain working of Core Java enum with example.

Ans. Java enum declares set of related constants avoiding duplicates or invalid values. Common is to define enum singleton instance pattern:

public enum OrderStatus {
Accessing values then is just:
OrderStatus status = OrderStatus.APPROVED;

This adds type-safety over plain constants.

Q112). How is Core Java Heap space structured? What core subspaces constitute Heap?

Ans. The Java Heap space comprises of key regions:

  • Young Generation – newer short lived objects
  • Old/Tenured Generation – long lived objects
  • Permanent Generation – Metadata like classes, methods etc

Tuning these subspaces for sizing/ratio is key for efficiency, which you can further learn about in our remaining Java interview questions.

Q113). What is Core Java string pool? Why prefer String over stringbuffer?

Ans. Java string pool refers to cache of literal string instances allowing reuse. As String objects are immutable, thread safe with reuse they are preferred over StringBuffer which would create new string buffer objects per invocation. String pool saves heap memory costs.

Q114). Can threads share common objects without synchronization?

Ans. Yes, threads can share common objects like:

  • Immutable objects
  • @Immutable annotated
  • Concurrent collections
  • ThreadLocal instances
  • Atomic classes
  • Local variables

These provide inter-thread communication safely avoiding synchronization costs.

Q115). What are best practices related to Core Java exceptions?

Ans. Some best practices around Java exceptions are:

  • Use checked exceptions only for recoverable cases
  • Avoid returning nulls, nested try blocks
  • Custom exceptions should be sensible
  • Map lower level causes to domain exception
  • Document exceptions thrown
  • Log exceptions along with context
  • Exception handling needs deliberation.

Q116). How does garbage collection process work in Core Java? How can it be tuned?

Ans. Garbage collection automatically manages deallocation of unused objects determining unreachable ones and clearing them. Tuning aspects involve:

  • Stricter object scoping
  • Handling long living objects separately
  • Avoid finalizers
  • Reduce number and size of objects created
  • Using concurrent low pause collectors

Tuning collectors for throughput or latency is key. To know more, you should explore our other core Java interview questions.

Q117). What is Java annotation? What can annotations be used for?

Ans. Java annotation provides metadata about the program embedded in code. Annotations have no direct effect on operations. Common uses are:

  • Compile time instructions for code generation
  • Insert checks like @Deprecated @Override
  • Spring framework processes them for configuration
  • Custom annotations can be created
  • What is difference between Heap and Stack memory usage in Java?

Objects live in Heap while execution contexts allocate associated stack with threads. Stack contains method specific variables, arguments, registers and return address. Stacks follow LIFO order to keep track of method calls ensuring cleanup. Heap handles objects providing more dynamic allocation whose lifecycle is disjoint from stack frames.

Q118). What is industry standard way of generating getters/setters/constructors in Java IDE?

Ans. IDEs like Eclipse, IntelliJ provide shortcuts to generate boilerplate code like getters/setters by right click on field and selecting options like Generate Getters and Setters. Libraries like Lombok reduce this effort using annotations transforming code on compilation. Using IDE productivity features is highly encouraged.

Q119). What are Java access modifiers? What is the difference between private and protected accessibility?

Ans. Java access modifiers provide scope access for classes, constructors, variables and methods. The levels are:

  • public - Entire application can access
  • protected - Accessible within class and its subclasses
  • default/package - Within same package
  • private - Strictly only inside class

Encapsulation gets enforced appropriately. To know more about this concept, feel free to check out our Core Java online training course.

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Q120). How can iteration be skipped in the foreach loop in Core Java?

Ans. The foreach loop hides access to the iterator directly. To conditionally skip iterations if required logic is complex, prefer enhanced for loop:

for(Temperature temp : temperatures) {

  if(temp.getValue() < 20 xss=removed>

This allows control via standard looping constructs.

Q121). What is Core Java Reflection API? What use cases can reflection be leveraged for?

Ans. Reflection API provides inspection abilities of classes, interfaces, methods fields during runtime discoverying them programmatically without needing compile time knowledge. This helps:

  • Mapping remote service requests to functions
  • ORM frameworks like Hibernate instantiating entities
  • Application performance monitoring
  • Alternate to expression evaluation rules engine

Q122). Can Core Java finalize() throw exceptions?

Ans. Yes, unlike constructors - finalize methods can throw exceptions which will just be logged and ignored by GC granting deference to cleanup in finalization. However exceptions should be avoided in finalizers expecting them to run interrupting GC. Instead resources should be closed correctly via try finally constructs.

Q123). What is the difference between heap vs stack memory usage in Core Java?

Ans. Java Heap region handles dynamic object allocation at runtime. Stacks contain thread specific method execution contexts and tracking containing local variables, arguments, registers, return addresses to keep track of method calls similar to a stack data structure. This is one of the major Java interview questions that you can't ignore at any cost.

Q125). How to initialize an array and avoid NullPointerException in Core Java?

Ans. Arrays in Java by default initialize to null for references, and default values for primitives. To avoid NullPointerErrors, arrays can be initialized proactively:

String[] teams = new String[10]; 
Arrays.fill(teams, "Unknown");

This avoids unexpected null interpretations later.

Q126). What is Java API specification? Which body defines standard architecture?

Ans. Java API specifications provide standard definition of classes, interfaces serving as reference implementation to ensure inter operability between Java runtime environments. The specifications are defined and updated in coordination by the Java Community Process (JCP) in tandem with OpenJDK as a reference model open source implementation providing these APIs.

Q127). Explain Shallow Copy vs Deep Copy approaches in Core Java transforming object state.

Ans. Shallow copy constructs new instance and inserts references to the same objects member fields refer. Shallow copies are cheap but may reflect changes later.

Deep copy iterates fields deeply creating duplicate nested object graphs fully decoupled from original objects. Immutability patterns help share buffers.

Q128). What is marker interface in Core Java? What special info does Java runtime use it for?

Ans. A marker interface does not declare any members itself but provides runtime type information to the compiler and JVM. Some examples are:

  • Serializable - Can serialize object state safely
  • Remote - Available for RMI remote calls
  • Cloneable - Object copies feasible without exceptions

This allows building metadata for marked objects. To know more about this, check our our Java training course.

Q129). Why is char array preferred over String for password field?

Ans. String is immutable causing retention in memory until Garbage Collected. Whereas char array state can be overwritten quickly after usage, clearing sensitive data deterministically. Strings also get output in heap dumps which can be probed later. Hence char array is a better choice for security reasons.

Q130). What is the difference between ArrayList and Vector in Core Java?

Ans. Both are index based iterable interfaces backed by dynamic arrays. Key differences are:

  • ArrayList is unsynchronized while Vector is synchronized impacting speed
  • Vector handles thread safety increasing overheads
  • ArrayList newer implementation is preferred

Choosing between them depends on synchronization needs.

Q131). How are dental ETF conteneurs different from directly synchronized collection classes?

Ans. CopyOnWriteArrayList, ConcurrentHashMap and ConcurrentSkipListSet are highly optimized concurrent collections relying on snapshots, clever sequencing avoiding locks allowing parallel reads improving throughput while changes reflected later. Comparatively synchronized collections use stricter mutual exclusion lowering scalability.

Q132). What is the difference between Instant and LocalDateTime in Java 8 Date Time API?

Ans. Instant represents timestamp with precision upto nanoseconds representing point on timeline (epoch/UTC) without timezone info.

Whereas LocalDateTime encapsulates date and time keeping timezone aspects making it more appropriate for common use cases like database columns, UI display etc.

Q133). How does the break statement inside the try-catch block behave?

Ans. Break statement inside try block immediately transfers control outside enclosing try-catch statement similar to return avoiding rest of try or catch blocks execution.

This helps avoid further unnecessary processing like cleanup on failures confined within the try block. If you are interested to know more about such core Java interview questions, feel free to let us know.

5 Essential Tips For Your Java Interview Preparation

  • Java is undoubtedly the most fast-growing and in-demand programming language and many of the product-based companies like Facebook, Amazon, Google, Microsoft look for the best talent when hiring Java experts. Here’s how I may prepare for our next Java interview:
  • Prepare all the essential topics like Java fundamentals, Data structure & algorithms, object-oriented programming & concept, Java collection framework, data structures, Java best practices, XML processing in Java, Garbage collection, SOLID design principles, Java IO and NIO JDBC, JUnit, to mention a few. Check the complete curriculum.
  • Check out questions asked by top companies like Google, Morgan Stanley to brush up your knowledge.
  • Enroll in an online certification course to get the foundation and advanced knowledge of Java along with preparation-related guidance.
  • Look for the best online Java tutorial to practice what you have learned. 
  • Have command over the commonly used technologies like spring framework, JPA, and hibernate. 

We are sure that these 39 Java interview questions and answers and our preparation tips will help you put your best foot forward. 

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Core Java is a very popular programming language that can be found in the technology stack of every company. No matter if you are heading for the Java developer interview or full-stack developer interview, knowing Interview Questions for Java with their answers is important for you to give your best and get hired in your dream company.

These are core Java interview questions for experienced and entry-level candidates that are often asked on repeat, so prepare them and give your best shot in an upcoming interview. Also, along the journey, never underestimate the Java role as its future scope is quite bright.

In case you are looking for complete preparation of Core Java Career, get along and explore our Java Training course online, led by real-programmers with real-time industry projects, along with complete resume feedback and impactful preparation of Core java interview questions and answers for experienced & freshers.

Let us know in the comments below if you have any queries or questions related to these core Java interview questions for experienced & beginners!


Q1. What will I learn in JanBask's Core Java Certification course?

Ans: You will master core Java concepts like OOPs, Exception Handling, Multithreading, Collections etc. The course covers Java 8 features like Lambda Expressions, Method References and Functional Interfaces. You will learn Core Java application development using Spring Boot, Hibernate and popular Java frameworks. The course culminates with Core Java certification preparation.

Q2. What are the benefits of doing this Core Java course?

Ans: Doing this course helps you learn Core Java in a structured format from industry experts. You will be able to develop complex Core Java applications for modern software needs. The course helps prepare for Core Java certification which validates your skills and boosts your career growth.

Q3. Why should I enroll for JanBask's Core Java certification course?

Ans: JanBask is a reputed online training provider known for quality content and expert trainers. The Java course is comprehensive, covers latest Core Java features and focuses on practical application development. JanBask offers mentor guidance and interview preparation support which maximizes your chances of getting hired as a Core Java developer.

Q4. What is the course duration and study time required?

Ans: It is an 8 weeks long course. You need to allocate around 10-15 hours per week for studying course materials, doing coding exercises, assignments and preparing for assessments. The self-paced online model offers flexibility to balance learning with other commitments.

Q5. What background do I need for doing this Core Java course?

Ans: Basic programming experience in any language is required. Familiarity with concepts like variables, data structures, loops, functions etc. is expected. Prior object oriented programming experience is beneficial but not mandatory.

Q6. Do I need to appear for any certification exam?

Ans: Yes, the course includes preparation for Oracle Certified Professional Java SE 11 Developer (OCPJP) exam. JanBask will provide all the required training, mock tests and study resources to appear and clear this credential exam which validates your Java skills.

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