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Java is a programming language and also a platform for computing. 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.
For a Java enthusiast who is looking to attend a Java 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.
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.
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.
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.
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.
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.
Ans:- A class, in the environment of Java, are some templates that are used for object creation, and to define certain object data types and their methods.
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.
Ans:- The classes that “wrap” the primitive data type into an object of that class are called Java wrapper classes.
Here are the Java interview questions and answers for experienced professionals who have gained some experience and are looking to upgrade their career.
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.
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.
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 Java object is subjected to garbage collection when the object is not reachable to the program in which it is used.
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.
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”.
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.
Ans:- A Servlet in 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.
Ans:- Here is the life-cycle of a Java Servlet-
Ans:- Request Dispatcher is a Java interface that is used to forward a request to some other resource which can be HTML, JSP or any other Java servlet within the same application.
Ans:- Follow the given steps to connect to a database in java-
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-
Here are the top Java interview questions and answers for experienced senior developers you should study.
Ans:- The applet is a Java program that is designed for transmitting the 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.
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.
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.
Ans:- Equals and hashcode methods are to be implemented In order to use any object as Key in HashMap, in Java.
Ans:- 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.
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.
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.
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.`
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 Java virtual machine (JVM) to the instruction set of a specific CPU.
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.
Ans:- The collection of related classes and interfaces grouped together is Package in Java. It enables developers to easily modularize codes. Packages help in providing easier access control on the code.
Ans:- Final is a special keyword in 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 Java.
Ans:- Java has four types of inheritance namely:
Ans:- The most important feature of 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.
Ans:- Classpath is related to Java executables, used to locate class files. Path, on the other hand, exists in an operating system used to locate executables.
Ans:- Both serialization and deserialization are crucial to stream handling in Java. Through serialization, you convert an object into a byte stream, and through deserialization, you simply undo the process.
Ans:- A ternary operator is a conditional operator in Java used to decide what values to be assigned to a variable.
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.
Ans:- As of Sep 2021, Java 17 is the latest release. Also, it is the next long-term support version (LTS) after Java 11.
These are some of the most asked interview questions you should prepare for your next Java Interview. Read our next section for the most essential interview tips.
Ans:- C++ is not platform-independent; the main concept behind it, “write once, compile anywhere.” Since the byte code generated by the 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.
Ans:- Some of the significant features of Java Programming Language are:
Ans:- Here is the difference:
HashSet: It is implemented through a hash table and permits the null object.
TreeSet: implements SortedSet Interface that uses trees for storing data.
HashSet: It permits the null object.
TreeSet: It does not allow null objects.
HashSet: It does not maintain elements in an ordered way.
TreeSet: It maintains elements in a sorted way.
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.
Ans:- It is a runtime API used to inspect and change the behavior of methods, classes, and interfaces. 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.
Ans:- A collection of Strings stored in heap memory is called 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.
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.
Ans:- Inheritance in 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.
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.
Ans:- JSP stands for Java Servlet Page. The JSP page contains two types of text- Static Data and JSP elements.
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 System.in represents InputStream object which by default represents standard input device, i.e., keyboard.
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.
We are sure that these 39 Java interview questions and answers and our preparation tips will help you put your best foot forward.
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.
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This is Puja Bhardwaj, a creative writer, and content strategist. I’m passionate about storytelling through written and visual content, and market that content for cultivating a committed audience. I come to the table with 5 years of content writing and marketing experience (in the agency, in-house, and freelance writing).
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