Going for a job or even an internship interview is not easy for anyone, but being properly prepared for it can give your confidence a boost. Hence, if you have an interview for a Java development position, then it is important to gain an understanding of what you might be asked. Your preparation process for acing the interview should ideally start off with the right set of Java Interview Questions.
Traditionally, most java-based interviews used to focus majorly on the differences between programming languages. But today, the questions have become more advanced, and proper java training shall be needed to answer them. In addition to having a good degree of java knowledge, you should also know the basics of SQL and Linux, coding, software, networking fundamentals, and more at these interviews. You might also be asked questions associated with data structures, algorithms, and NIO patterns.
As Java is majorly used as an application programming language, interview questions linked with this domain put emphasis on API and core concepts. While there is no guarantee of what questions shall be asked at your relevant Java interview, gaining proper knowledge about the concepts associated with it and going through some frequently asked questions can increase your odds of faring well in it. For best outcomes, you may even join Java certification courses where important topics associated with Java shall be taught in a comprehensive manner.

Common Java Interview Questions


Q 1-) Why is Java a platform-independent language?

Java was developed in a manner that doesn't depend on any kind of software or hardware. Instead, code is compiled by a compiler, which converts it into a platform-independent bytecode that can be run on several systems.

Q 2-) Why can Java not be a pure object-oriented language?

As Java supports char, short, byte, long, boolean, int, and such primitive data types, it cannot be considered a pure object-oriented language.

Q 3-) What are the major benefits of using Java?

Being a high-level object-oriented programming language, Java can be used for developing applications, games, and device systems. In addition, it is platform-independent, swift, dependable, and fast.

Q 4-) What is meant by Class and Object?

An object can be described as a collection of methods. Classes essentially execute operations and represent their state. Class is used for the purpose of defining new types of data that are subsequently used to create objects.

Q 5-) What do JRE, JDK, and JVM imply?

JVM (Java Virtual Machine) provides a runtime environment for codes needed to be executed, while JRE (Java Runtime Environment) can be referred to as a collection of whiles required during runtime by JVM. JDK (Java Development Kit is ultimately used for writing and executing a program. It features JRE alongside certain development tools.

Q 6-) Does all property of Immutable Objects have to be finalized?

No, this is not necessary. It is likely to achieve the same functionality by making members private but at the same time non-final and not making any modifications to them except in the constructor. Do not leak any reference for that member if it is a mutable object, and do not provide a setter method for them as well. It is important to remember that making a reference variable final just makes sure that it shall not be re-assigned a distinguished value. However, one may still change individual properties of an object pointed by the relevant reference variable. 
(This is among the popular Java Interview Questions.)

Q 7-) What does looping imply?

Loops tend to be used for executing a block of statements or even just a particular statement repeatedly. Loops are categorized into three types, Do While Loops, While Loops, and For Loops.

Q 8-) What is the key difference between Overriding and Overloading?

A situation where the two methods have the same properties and name but occur in a child and parent class, respectively, is known as Overriding. On the flipside, Overloading implies two methods with different properties but the same name. 

Q 9-) What does Inheritance imply?

With Inheritance, one is able to let a derived class acquire methods from a base class.

Q 10-) What is the JIT compiler?

An abbreviation for Just-In-Time, JIT is used with the aim of augmenting performance during the run time. Compiling parts of byte code that has similar functionality simultaneously are conducted by it to minimize the compilation of time involved in running the code. A compiler is a translator of source code to machine-executable code. JIT compiler essentially is a part of JVM. This is among the most interesting Java Interview Questions.

Q 11-) Is restricting Inheritance possible?

Yes, one can opt to restrict Inheritance by making use of the method final or using the final keyword. It can also be restricted through a private constructor or (//) Javadoc comment.

Q 12-) What is meant by Content Negotiation?

Content Negotiation takes place between the host server and the user. For example, while making an HTTP request, the user shall get their result in varied formats and languages. They subsequently can specify the content that they would accept back from the host through content negotiation.

Q 13-) What does WORA mean?

WORA also known as Write Once Read Anywhere. It essentially is the property of a language to be run on any platform. Owing to its bytecode nature, Java is allowed in this property. However, it is not platform-specific, as WORA is somewhere between a source code and machine code.

Q 14-) How can deadlock be avoided in Java?

By breaking circular wait conditions, it is possible to avoid deadlock in Java. However, to do so, one must make arrangements in the code for imposing the ordering on the acquisition and the release of locks. If the lock is acquired in a consistent manner and released in the opposite order, a single thread holding a lock acquired by another will not take place and vice versa.

Q 15 -) Why is a constructor important?

Constructors are used for initializing the state of an object. If the user creates a new object with the usage of a new keyword, a default constructor shall get invoked. It additionally should have a similar name to the class name.

Q 16-) Is it possible to override static methods?

No, it is not likely to override static methods. While the declaration of static methods with the same signature can be made in the subclass, runtime polymorphism can't take place in these cases. Instead, dynamic polymorphism or overriding takes place during the runtime. However, static methods are loaded and looked up at the compile time statically, and they cannot be overridden as a result.

Q 17-) What would be the core objective of garbage collection?

Freeing up valuable memory space that has been occupied by unreachable and unnecessary objects during the Java program execution is the core objective of garbage collection and is done by deleting such objects. This is done with the aim of making sure that the memory resource is used competently. Conversely, it also does not offer any guarantee that there shall be adequate memory for the program execution.

Q 18-) What shall be the use of composition?

The composition can be used for holding the reference of one class within another class. In this situation, the contained object is not able to exist without the class that contains it, and it subsequently is a type of aggregation.

Q 19-) What is meant by annotation?

Annotation is simply a tag that is used with the aim of symbolizing metadata representing a certain field, interface, class and so on. It is generally used by the JVM and the compiler and does not directly influence the operations.

Q 20-) When it comes to storing confidential data, why is character array usually opted for over string?

A string cannot be modified in Java. Till it is not removed as garbage, it shall stay in the string pool subsequently to the declaration. Thus, string stays in the heap section of the memory for an unspecified and unregulated span of time after the execution of string value processing.
Hence, hackers can steal important data if a memory dump is accessed by them illegally. Such risks are not prevalent in character arrays, as they are mutable objects. As the work of the character array variable is completed, the variable can be promptly configured to blank.
These were some of the common Java Interview Questions. Going through them would give you a better idea of what you can expect in your upcoming interviews. In case you find your knowledge to be lacking, then you may always get enrolled into a java se7 programming course or a similar program. 
Armin Vans
Archer Charles has top education industry knowledge with 4 years of experience. Being a passionate blogger also does blogging on the technology niche.



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