Top 51 Java Interview Questions for Freshers & Advanced Professionals

Introduction

Somebody has appropriately said that interviews are more unpleasant than the course itself is. Ordinarily, we simply wish that we don't need to do that whole one on one session. Try not to stress, we are here to scoop you out of the pressure that you may experience for your interview identified with Java Developed. We have gathered an article for you that will enable you to nail your meeting like an ace. In this specially designed Java interview question and answer for freshers & experienced blog, we are going to let you know some of the most important Java Interview Questions and Answers that will definitely give you an edge and set your class apart in the interview process. Every single IT company, big or small, requires Java developers. Java Influences everything, starting from Android to the ecosystems of Hadoop. The career in Java is very promising; the individuals working in this sector have reported that an average yearly remuneration of $70,376 is likely to be received by a fresher.

Top 51 Java Interview Questions And Answers for Freshers & Professionals

For the person looking forward to attending a JAVA interview soon, here is a list of some of the most popular interview questions and answers which will help you in the right way. Here, we have included the top most frequently asked questions along with relevant answers to help out freshers and the experienced professionals appropriately.

Java Interview Questions and Answers for Freshers

If you are applying for entry-level Java programming positions, here are the Java interview questions and answers for freshers.

Q1). Explain what is Java?

Java is an object programming language that was premeditated to be moveable across several platforms and operating structures. This language was developed by Sun Microsystems. Java is exhibited after the C++ programming language and comprises special structures that make it perfect for programs on the Internet.

Q2). Explain the Meaning of Static in Java?

• Static stands for one per class, not one for every object no matter how various instances of a class might occur. This entails that you can use them deprived of generating an instance of a class.
• Static methods are indirectly final since overriding is done grounded on the type of the object and static approaches are involved in a class, not an object.
• A static technique in a superclass can be followed by an alternative static method in a subclass if the unique method was not acknowledged as final.
• Though, you can’t overrule a static technique with a non-static technique. In other words, you can’t modify a static technique into an illustration method of a subclass.

Q3). Why is Java Perceived to be Platform-Independent?

This is because platform-independent is the term that means “write once run anywhere”. Java is referred to because of its bytecodes that have the capacity to run on any system or device whatsoever irrespective of the underlying operating system.

Q4). Why is JAVA not 100% Object-Oriented?

Java is not cent percent object-oriented because it utilizes eight types of primitive datatypes named boolean, byte, char, int, float, double, long, short which are not objects.

Q5). Explain Constructors in JAVA?

In the Java framework, the constructor is the term that refers to a block of code that is usually used to initiate an object. It should have the same name as that of its class.

Q6). How many Types of Constructors are there in JAVA? 

There are two types of constructors in JAVA:

• Default constructor
• Parameterized constructor

Q7). What is a Singleton Class and How can we Make a Class Singleton?

Singleton class is a class whose only one instance can be created at any given time, in one JVM. A class can be made singleton by making its constructor private.

Read: What is Java String? How to Declare String Array in Java with Example

Q8). Is it Possible to Override a private or a Static Method in Java?

No, there is no provision to override a private or static method in Java. However, you can use method hiding approach in extraordinary cases.

Q9). What do you Mean by Association?

Association refers to a relationship where all the objects of the class have got their own lifecycle and there is no owner as such. These relationships or associations as we call them can be one to one or one to many or many to one or many to many.

Q10). Explain the Concept of Aggregation in JAVA?

Aggregation is a concept in JAVA for a specialized form of Association where all the objects have got their own lifecycle but there is ownership and the child object cannot belong to another parent object in any manner.

These were the java freshers interview questions, now let’s move towards the questions asked by the seniors.

Q11). What is a classloader?

It is a subsystem of JVM that is used to load class files. When we run any Java program, it is loaded first by the classloader. There are three built-in classloaders in Java- Bootstrap ClassLoader, Extension ClassLoader and System/ Application ClassLoader.

Q12). What do you mean by data encapsulation?

It is the mechanism that helps in the implementation details of a class are kept hidden from the user.

Q13). What is the main objective of garbage collection?

Freeing the heap memory by destroying the unreachable objects is the main purpose of garbage collection.

Q14). What are the differences between JVM, JRE and JDK in Java?

JVM: It stands for Java Development Kit that is used for code development and execution. 

JRE: It stands for Java Run Environment, JRE is used for environment creation to execute the code. 

JVM: It stands for Java Virtual Machine and is used to provide specifications to implement to JRE. 

 Q15). What do you understand about Java virtual machines?

This is a virtual machine allowing the computer to run the Java program. It acts like a run-time engine that calls the primary method of Java code. It is more like a specification that must be implemented in the computer system. 

Here is a complete guide on How to Become a Java Developer. 

Q16). What are the advantages of Packages in Java?

Packages in Java helps in avoiding name clashes, providing easier access control, locating the related classes, etc. 

Q17). Explain the Externalizable interface.

The externalizable interface is helpful in having control over the serialization process. Just like the serializable interface, it is a class that implements the Externalizable interface and is marked to be persisted. 

Q18). What is Multithreading?

It is a process to execute different threads simultaneously. Multithreading is generally used for multitasking. It consumes less memory and provides fast and effective performance.

Q19). Explain Java String Pool.

Java String Pool, also known as String Intern Pool, is a storage area in Java heap where string literals store. 

Q20). What is inheritance in Java?

Inheritance is referred to one class that can extend to another. So that the codes can be used again from one to another class. The existing class is referred to as the Super class whereas the derived class is known as a subclass. 

Q21). What is the purpose of encapsulation in Java?

The purpose of encapsulation is to protect the code from others and maintain codes smoothly. 

Q22). What is a Map in Java? 

It is an interface of Util packages that maps unique keys to values. Map interface is not just a subset of the primary collection interface and hence it works in a different way. 

JAVA Interview Questions and Answers for Experienced

Q23). What is a Servlet?

In JAVA atmosphere a Java Servlet is a server-side technology used to extend the capability of the web servers by providing support for dynamic response and data persistence.

Q24). What do you Understand about Request Dispatcher?

Request Dispatcher interface in JAVA is used to forward the request to another resource which can be HTML, JSP or any other servlet within the same application.

There are two methods defined in this interface:

• void forward()
• void include()

Q25). Is it Possible to Generate Array Volatile in Java?

Yes, you can generate an array volatile in Java but then again only the situation is directed to an array, not the entire array. This means that, if one thread deviates the reference variable to direct to the extra array, that will offer a volatile assurance, but if multiple threads are altering separate array elements they won’t be having ensues before assurance offered by the volatile modifier.

Also read: Java Developer Role & Responsibilities

Q26). Explain the Concept of Interfaces in JAVA?

Interfaces are gentler in performance as compared to abstract classes as additional indirections are compulsory for interfaces. An additional key factor for designers to take into deliberation is that any class can spread only one abstract class through a class that can implement numerous interfaces. Use of lines also places an additional burden on the developers at any time an interface is executed in a class; the developer is required to contrivance each and every technique of interface.

Read: What is A Java Constructor? Type of Constructors & Uses in Java

Q27). What are Real-World Practices of Volatile Modifiers?

One of the real-world uses of the volatile variable is to generate interpretation double and long atomic. Equally double and long are 64-bit extensive and they are recited in two parts, primary 32-bit first time and following 32-bit another time, which is non-atomic but then again volatile double in addition long read is atomic in Java. Additional use of the volatile variable is to deliver a recall barrier, just like it is cast-off in the Disruptor framework. Fundamentally, the Java Memory model pull-outs a write barrier. Subsequently, you write to a volatile variable besides a read barrier beforehand you read it. That means, if you inscribe to volatile field then it’s definite that any thread retrieving that variable will see the worth you wrote and everything you did beforehand doing that correct into the thread is certain to have occurred and any rationalized data values will also be noticeable to all threads since the memory barrier flushed all additional writes to the cache.

Q28). Explain the meaning of Thread-local Variable in Java?

Thread-local variables are variables limited to a thread, it’s like a thread's individual copy which is not public between numerous threads. Java offers a Thread Local class to care for thread-local variables. It’s one of the numerous ways to attain thread safety. Though be cautious while using thread locally adjustable in managed environments e.g. with network servers where operative thread out lives somewhat application variables. Somewhat thread-local variable which is not detached once its work is done can possibly reason a memory leak in Java application.

Q29). Explain the Meaning of platform?

A platform is the hardware or software setting in which a program executes. Maximum platforms in JAVA can be defined as a grouping of the operating system and hardware, Windows 2000/XP, Linux, Windows 2000/XP, MacOs and Solaris.

Q30). What’s the variance amid an Abstract Class and Interface in Java?

The main difference amid an abstract class and interface is that a boundary can only own assertion of public static approaches with no existing application while an abstract class can have associated with any admittance specified (i.e. public, private, etc.) with or without real implementation. Additional key variance in the usage of abstract classes and lines is that a class that gears an interface must contrivance all the approaches of the interface while a class that receives from an abstract class doesn’t need the execution of all the methods of its superclass. A class can instrument numerous interfaces but it can spread only one abstract class.

Q31). What is the variance amid an Inner Class and a Sub-Class?

An Inner class is a class that is copied up to the additional class. An Inner class has admittance privileges for the class which is nesting it and it can contact all variables and systems well-defined in the outer class, whereas a sub-class is a class that receives from another class named Superclass. Sub-class can contact all public and protected approaches and fields of its superclass.

Q32). Can we affirm a class as Abstract Deprived of having an Abstract Method?

Yes, we can generate an abstract class via abstract keyword beforehand class name even if it doesn’t have any abstract method. Though, if a class has even one abstract technique, it must be acknowledged as abstract or else it will give an error.

Q33). Can Volatile Generate a Non-Atomic Process to Atomic?

This additional good question I prefer to ask on volatile, typically as a follow-up of the preceding question. This query is also not simple to respond since volatile is not about atomicity, but there are situations where you can practice volatile flexibility to make the operation atomic. One instance I have seen is having a long arena in your class. If you distinguish that a long field is retrieved by extra than one thread e.g. an application, a value field or everything, you will make it volatile. Why? Since reading to an extended variable is not atomic in Java and done in double steps, if one thread is lettering or apprising long value, it’s probably for the additional thread to see half value (fist 32-bit). While interpretation/writing a volatile long or dual (64 bit) is atomic.

Q34). Explain wait-notify code for the producer-consumer situation?

Please understand the response for a code example. Just recollect to call wait () and inform () technique from the coordinated block and test waiting for ailment on the loop as an alternative of if block.

Read: How to Convert Char to Int in Java

Q35). Explain Thread-Safe Code Singleton in Java?

Please understand the answer for a code instance and stage-by-stage guide to generating thread-safe singleton code in Java. As soon as we say thread-safe, which means Singleton should continue singleton even if low-level formatting occurs in the case of numerous threads. Using Java enum as Singleton class is one of the simplest ways to generate a thread-safe singleton in Java.

Q37). What are the Performance Inferences of Interfaces Over Abstract Classes?

Interfaces are gentler in performance as compared to abstract classes as additional indirections are compulsory for interfaces. Additional key factor for designers to take into deliberation is that any class can spread only one abstract class through a class that can implement numerous interfaces. Use of lines also places an additional burden on the developers at any time an interface is executed in a class; the developer is required to contrivance each and every technique of interface.

Q38). Explain Reason that why is a compile-time persistent in Java? What is the risk of using it?

Public static ultimate variables are also recognized as a compile-time endless, the public is non-compulsory there. They are swapped with definite values at compile time since the compiler distinguishes their value up-front and also distinguishes that it cannot be changed throughout run-time. One of the problems with this is that if you used a public stationary final variable from some in-house or third-party library and their worth changed, then your client will still be using the old value even after you organize a new version of JARs. To evade that, make certain you compile your program when your elevation dependence JAR files.

Q39). Why does Java not accompany manifold inheritances?

Java development team hit to make Java as

• Unpretentious, object-oriented, and acquainted
• Vigorous and secure
• Architecture unbiased and transferrable
• Extreme performance
• Understood, threaded and lively
• The details for overlooking Multiple Inheritance from the Java Language regularly stem from the unassuming, object-oriented and acquainted goal.

Q40). What are the observer and observable classes?

Observer is any object that wants to get notified when the stage of another object changes. While observable is any object whose stage might be interested, and in whom another object may get its interest listed. 

Q41). What are the different ways to handle exceptions?

There are mainly two ways to handle exception:

First is using try/catch: This risky code is surrounded by try blocks. Under it, when an exception occurs, then it is caught by the catch block. 

The second way is by declaring throws keyword: Here, at the end of the method, we can declare the exception by using throws keyword. 

Check Java Developer Resume Guide.

Q42). What is meant by Serialization?

Converting any file into a byte stream is referred to as Serialization. The objects of the field are converted into bytes for security reasons. 

Q43). Can a constructor return a value?

No, there are return value statements in the constructor. 

Q44). What is a JIT compiler?

JIT stands for Just-in-Time compiler, it is basically a program to convert the Java bytecode into instructions, sent directly to the processor. JIT compiler is enabled by default in Java, it is activated when a Java method is invoked. 

Q45). What are the Memory Allocations available in JavaJava?

The memory allocations are available into three parts, namely Code, Stack, Heap, and Static.  

Q46). What are the different methods of session management in servlets?

A conversational stage between the client and server, sessions can consist of numerous requests from client and server. Since HTTP and Web Server are stateless, the only way to maintain a session is when some unique info is passed through the client and server in every response. 

Q47). What is Hibernate Framework?

Hibernate Framework is the programming technique that maps application domain model objects to the relational database tables. The Hibernate Framework provides the option to map plain old java objects to traditional database tablets with JPA annotations and XML configuration. 

Q48). Top Java Interview Question: What are the important benefits of using Hibernate Framework?

Here is the list of major benefits of using Hibernate Framework:

• It eliminates all the boiler-plate code that comes with JDBC and takes care of managing resources. 
• It supports XML and JPA annotations, which makes code implementation independent. 
• It is easy to integrate with other Java EE frameworks, it is quite famous that Spring Framework comes up with built-in support. 

Q49). What is the difference between Error and Exception?

An eros is an irrecoverable condition that occurs at the runtime. Exceptions are conditions, occurring because of bad input or human error. 

Q50). What purpose do the keywords final, finally, and finalize fulfill?

• Final: It is used to apply restrictions on class, variable, as well as method. 
• Finally: It is used to place significant code, executed whether the exception is handled or not. 
• Finalize: It is used to perform cleaning processing just before the object is garbage collected. 

Q51). What is the difference between a local variable and an instance variable?

A local variable in Java is mainly used in a method, constructure, or a block and has a local scope. While, an instance variable is a variable that is bound to its object itself.

Check Core Java Interview Questions if you are looking to do job in core Java.  

Final Thoughts on Java Interview Question and Answer for Freshers & Advanced Professionals!

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 developer fresher & advanced professional is important for you to give your best and get hired in your dream company.

Every above Java interview question for fresher & advanced professional is asked on repeat, so prepare them and give your best shot in an upcoming interview.

In case you are looking for complete preparation of 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 Java interview questions for freshers and experienced.

Let us know in the comments below if you have any query or questions related to these Java experienced or Java freshers interview questions and answers.

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