Top Common Java Interview Questions in 2022 | Optymize

Java at present has a claim as one of the most popular, if not the most popular programming language at present among developers. So, any aspiring developer must have a working knowledge of the language, so to get an accurate judgment in regards to their capability, here are some common java interview questions to assess them. This article will cover not only such java interview questions but also various features, history, and other facets of the Java programming language.

Introduction to Java and its History and its Milestones
Java is a high-level, class-based, object-oriented programming language that was intended to be WORA (Write Once Read Anywhere). It means that it will have as few implementation dependencies as possible, allowing compiled Java code to run anywhere else without recompiling. This is thanks to the fact that Java applications are compiled to bytecode, which can run on JVMs (Java Virtual Machines). This makes the applications independent of the supporting computer’s architecture.
Java itself bears a lot of similarities in syntax to older languages like C and C++ in order for familiarity with programmers with previous experience in the latter languages. Outside of that, it also boasts additional features, programming libraries, and frameworks that have allowed it to claim a spot as one of the most common programming languages in the world today.
Java was initiated in 1991, and designed for use in interactive televisions, but the hardware at the time wasn’t advanced enough. As such, when it was released in 1996, its selling point was instead the familiar syntax and the WORA functionality. Other features like network and file access restrictions and configurable security made it fairly secure and it has found a willing user base with software developers and browsers for Java applets.
There are additional milestones in Java’s history that may often form the base of Java interview questions. These include 1997, where there was an attempt at standardisation, 2006 when the JVMs core code was almost in its entirety released as an open-source software and the dates when older editions were discontinued. These may seem like meaningless trivia, but they find some relevance when dealing with legacy code.

Beginner Java Interview Questions
The beginner Java interview questions refer to Java interview questions that are meant for the college intern or a beginner, junior level developer. Such Java interview questions are meant to ascertain whether the applicant has a working knowledge of the Java programming language. The applicants that are asked these sets of Java interview questions are likely to have only previous experience with Java in the form of practical classes and projects rather than actual work experience. Depending on how they answer the Java interview questions, additional training may be necessary, so they tend to cover both general as well as slightly advanced topics.

1. Explain about the Basics of Java This is one of the introductory Java interview questions that is asked in nearly every scenario for a newcomer. A lot of the features have been described in the previous section. However, it’s more than just a simple technical knowledge as it is often the source of justification for why they are choosing Java as a programming language of choice.
2. State the differences between Java and a similar programming language like C++ or C This is another one of the Java interviews questions that is expected for any Java newcomer in the field. When answering this question, they should be able to point out major factors such as platform dependencies, features like inheritance, overloading, calling, overriding, etc. Also refer to objectives, applications and language type.
3. Explain about the features and characteristics of Java This is one of the more flexible Java interview questions as many of the features can also be their own interview question. These can include features like abstraction and encapsulation along with the available primitive data types.
4. Define Java Bytecode The bytecode is responsible for Java’s claim to be written once, read anywhere. The Java compiler converts Java programs into bytecode, which is an intermediate between source and machine code and independent of the platform.
5. Define JVM (Java Virtual Machine), JRE (Java Runtime Environment) and JDK (Java Development Kit). Differentiate between them The two Java interview questions above are interrelated as many of the defining features can also be used to differentiate between them. For instance:
6. Java Virtual Machine: An abstract machine that provides the runtime environment.
7. Java Runtime Environment: Physically existing implementation of JVM as a set of software tools for developing Java applications.
8. Java development kit: It is an implementation of ME, SE or EE java platforms, consisting of JRE with development tools.
9. List the Default Data Types in Java This is one of the basic, yet deceptively tricky basic Java Interview Questions. While the eight, primitive data types are simple in terms of definitions and range, they are often reused in different programming languages, so it occasionally becomes a point of confusion among beginners, what data type belongs to which language. The additional questions in this topic can include the steps on how to convert data from one type into another and this overlaps with the topic of features of java.
10. Explain about Garbage Collection This is one of the primary features that is present in Java but it occasionally shows up separately among Java interview questions. As such, it has been presented here specifically as well.
11. Define Java’s JIT Compiler It is a specific type of compiler that compiles parts of the bytecode with similar functionality at the same time. As such, it reduces the compilation time and improves performance and is often a frequently referred topic among Java interview questions.
12. Define classloader. Define the types of classloaders Classloaders are a subsystem of JVM that is used to load class files. As such, it runs when the program is first run. The three types of classloaders are: the bootstrap classloader, the extension classloader and the system/application classloader.
13. Explain about class specifiers along with its categories Class specifiers are the keywords in Java that are used to define the access scope of the method, class or variable. It is an obvious topic for Java Interview Questions as it is frequently used in java projects. As such, the access specifiers and the four types and definitions of each are common topics of Java Interview Questions.

Advance Java Interview Questions

1. Define features like abstraction, encapsulation, inheritance and polymorphism, how they are utilised in Java along with comparisons between them. While the features of Java have been mentioned previously, the features here have to be mentioned separately as they are an intrinsic part of many languages and define their inner working rather than being just a selling point or as a nifty property. As such, most programming languages, including Java, include them in their interview questions. Outside of this, the implementation varies between languages and in the case of Java, its implementation there is common among Java interview questions.
2. Explain about Java constructors and constructor overloading Becoming java developers are a frequently covered topic in Java interview questions. They refer to a type of method that is used to initialise the state of any other state of an object and memory is allocated to it. There are two types of constructors in java based on their parameters: default constructors and parameters constructors. Outside of this, there are additional topics that can be covered under Java interview questions. These include returning value, inheritance, overloading and making static.
3. The “this” keyword in Java The “this” keyword in Java is often a part of Java interview questions. as a reference variable that refers to the current object. The questions here can range from definition to uses to specific questions regarding specific situations. Outside of this, there are some more specific Java interview questions as presented below to get an idea about their in-depth knowledge The “this” keyword acts ledge of core java rather than just their working knowledge. These include:
4. Can Java save a file with a .java extension? Among the in-depth Java interview questions, this isn’t that highly advanced but there are also additional conditions such as running by java classname.
5. Can you execute code in Java before the main method Yes, code in java written in the static initializer block is executed before the main method. However, in Java interview questions, a similar question is whether it can run without a main method.
6. Can you execute a program in Java without the main() method. Yes, if the code uses the static block. However, this only works for those preceding JDK 1.7.
7. Can you assign reference to this variable? No.
8. Can you predict the output of the code in Java? This has been presented as one of the more thorough Java interview questions but it takes so many different variations that it can be considered as an entire sub-section of Java interview questions. The topics can range from finding the output of a code when the code uses tricky syntax to obfuscate the output, error finding to judge whether a code would run, finding errors that are stated to exist along with solutions along with explaining their workings. EE Java Interview Questions J2EE refers to the Java 2 Enterprise edition. The main application for this is in developing and deploying multi-ti3r web-based enterprise applications. As such, it can often be found applicable in companies. As such, a section has been dedicated here for some of the questions that may be asked in regards to J2EE. Explain J2EE This bears similarity to the core Java interview questions that were mentioned in the previous section. The definition should include not just about the full name and what it means, but also the functionality and primary features. Explain about the J2EE module. Explain about the different types of J2EE modules The J2EE module refers to a software unit that contains one or more J2EE components for the same container type. Outside of the definition, function and types, the Java interview questions here can range from defining each subtype and what they contain and explanation for each section. Struts in the J2EE framework The struts refer to the application development framework that is based on the application development framework that is based on the MVC. Struts and their components are often referred to in Java interview questions, especially in EE due to their relevance for development. Hibernate in J2EE Hibernate is a query and object service that allows for the expression of queries better than in SQL. This is an integral part of J2EE and the questions here can range from the definitions of Hibernate and HQL to questions regarding its uses, advantages and limitations and steps regarding practical questions regarding adding of Hibernate mapping files abd file extensions for mapping and configure Spring in J2EE Similar to Struts above, Spring is a lightweight open-source framework for developing enterprise applications. Again, similar to Struts the questions can range from definitions and uses to modules and expanding on each section. Topics to cover outside of Java interview questions Outside of the posted questions above, as the role for hiring increases in seniority, such forms of theoretical Java interview questions decrease in relevancy. That is because the people hired at the senior roles are expected to know about such topics either from previous roles and are more likely to work in roles such as management of teams, testing of the product and handling of customer management so while they have latitude in looking up minutiae of code, they should have the knowledge and expertise in regards to complex and unexpected issues along with an ability to mentor subordinates in such issues. As such, rather than asking Java interview questions on theoretical topics, the focus should be on their work and project experience with the subject. Some examples of the miscellaneous Java interview questions that can be expected are as follows:
9. What previous experience do you have using Java?
10. What frameworks, packages and libraries have you used in collaboration with Java?
11. What challenges did you face in your projects?
12. What other experience do you have using software’s similar to Java such as C++? Outside of Java interview questions regarding previous work experience and theoretical knowledge, questions regarding their general technical knowledge base are also expected in any interview. Conclusion The presented Java interview questions are a brief summary of the many possible Java interview questions that can be asked on this subject. Additional Java interview questions are available online on many sites and blogs. This isn’t even considering the various libraries and frameworks that Java offers. As such, while a theoretical understanding is helpful, as stated in the penultimate section, that cramming such Java interview questions isn’t as helpful as clear comprehension and on-hands experience.