What’s up, Coders! Did you know that Java was originally named Oak, but was later renamed by Sun’s marketing department when lawyers discovered that there was already a computer company registered as Oak. What’s more interesting is that the “0xCafeBabe” magic number in the public class files of Java was named after the very same Café where Sun’s Java team used to chill out for coffee breaks. I mean, who can guarantee that savvy interviewers will not ask nerdy facts on Java? Which, as an avid Java programmer, is your key to impress an interview panel.
Add forward evolution with backward compatibility, Java has been the go-to language for developers with over 25 years of evolutionary improvement, that too, while continuing to implement major changes that serve community demands. Therefore, as a Java professional, it’s not just important to learn the right technologies but also to prepare the right answers to a few commonly asked Java interview questions that would guarantee a breeze-through to the next round.
Want to learn about – Problem-solving skills in java
15 Java Interview Questions And Answers
let’s get started with a common set of Java interview questions and answers for freshers with the foremost question being:
Q1: Briefly explain your understanding of Java?
Ans: Developed by James Gosling and further improved by Oracle Technologies, Java is a high-level, object-oriented, programming language that enables platform independency on Windows, Mac OS, and various versions of UNIX.
Q2: Briefly explain the common features of Java?
Ans: What’s unique about Java is that it offers higher cross-functionality as programs written in one platform can effortlessly be executed across different embedded systems. Here are the features that enables such functionality:
- High Performance Runtime: With its Just in Time (JIT) compiler, Java offers high-performance runtime where the JIT compiler converts the Java bytecode into machine language code which is then executed by the JVM.
- Multi-Threading: When programs are run, a thread is a flow of execution, where JVM creates a thread which is denoted as the main thread. Java enables the execution of multiple threads by extending the thread class.
- OOPS Concepts: Object Oriented Programming in Java is an approach that enables modular programs with a partitioned memory areas for both data and functions that can be used to create copies of similar modules.
- Platform Independency: Platform independency is one of the niche features of Java that utilizes the JVM or Java Virtual Machine to enable a single Java program to be executed on multiple platforms without changes.
Q3: Explain about Java Virtual Machine.
Ans: JVM or Java Virtual Machine is an abstract specification machine that provides runtime environment in which Java bytecodes can be executed; an implementation of which is also known as JRE (Java Runtime Environment).
Q4: What feature in Java enables high performance? Explain the process?
Ans: With Just-in-Time compilation (JIT) compilation in Java, the bytecode is translated into machine code and then directly executed at runtime. To enable high performance, the JIT compiler is enabled by default which converts the bytecode of the Java method into native machine code, following which, the Java Machine Language calls the compiled code directly instead of interpreting it. This enables a performance boost in code execution, hugely benefiting Java.
Q5: How has Java become a platform-independent language?
Ans: The objective of the development of Java was to enable cross-compatibility across multiple platforms, irrespective of the hardware or software running on the end machine. Java achieves platform independency by compiling the code and then converting it into bytecode. And since bytecode is cross-compatible across different embedded systems, Java, in turn, becomes platform-independent. However, to execute bytecode, the end machine must Java Runtime Environment (JRE) installed on it.
Q6: What is the difference between Heap and Stack Memory in Java? How does Java utilize both?
Ans: Already fixed before the execution of a program in Java, Stack Memory is a portion in the memory pool that is assigned to every individual program. In contrast, Heap Memory is the portion that is not allocated to Java programs before an execution but is readily available when a program needs it during runtime. In addition, Heap Memory also supports dynamic memory allocation, is tightly managed by the CPU and acts like a free-floating region of memory.
When a Java program is created, all its variables and methods are stored in Stack Memory. Whereas any additional objects in a Java program is created in the Heap Memory. However, Heaps are generally referenced from Stack.
Q7: Can we call Java a self-sufficient object-oriented programming language?
Ans: Since everything in Java is under its respective classes which can be accessed by creating objects, it’s not wrong If we call Java an object-oriented programming language. However, we cannot claim that Java is purely an object-oriented programming language as it has direct access to primitive data types like int, float, char, Boolean, double, etc. Therefore, Java is indeed an object-oriented programming language, but not-at-all a pure OOP language.
Q8: How is Java different from C++?
Ans: The primary difference between Java and C++ is that Java is written and compiled as an interpreted language, whereas, C++ is only a compiled language. Therefore, C++ can only run on the system it was initially compiled on.
Q9: An integral part of C++ is pointers. Why does Java not utilize pointers?
Ans: C++ being a compiled language hugely benefits from pointers. And since it’s quite a complicated language, in C++, usage of pointers is unsafe and complex. Java, on the other hand, focuses on code simplicity. However, by not implementing pointers, Java does furnish a certain degree of abstraction. Higher the usage of pointers, slower the procedure of garbage collection, therefore, Java utilizes references as these cannot be manipulated, unlike pointers.
Q10: Explain your understanding of an instance variable and a local variable. What are the differences?
Ans: An instance variable is accessed by all methods in the class and is declared outside the methods and inside the class. Such variables describe the properties of an object and will have a copy of a variable. Therefore, any changes will be affected on a particular instance. In contrast, local variables are present within a block or function, and can be accessed only inside them. Whenever a local variable is declared, other class methods aren’t updated about it.
Q11: What is data encapsulation in Java?
Ans: In object-oriented programming or OOP, data encapsulation is a concept of hiding attributes and behaviours in a single unit. This ensures modularity in the code so that each object independently has its own methods, attributes and functionalities.
Q12: Define wrapper classes in Java.
Ans: Wrapper classes convert Java primitives into reference types (objects). In Java, every primitive data type has a dedicated class, which are known wrapper classes since they “wrap” the primitive data type into a reference type.
Q13: Name and explain the constructors in Java.
Ans: Constructor is a block of code in Java that initializes an object and sets initial values for attributes. Requiring the same name as that of a class, a constructor is called by default when an object is created and has no return type.
- Default Constructors: Default constructors, in Java, are the no argument constructors to initialize instance variables, which will be created by default if any other constructor isn’t already defined by the programmer.
- Parameterized Constructors: Parameterized constructors, in Java, have a specific number of arguments to be passed and initialize instance variables with provided values. These are written explicitly by the coder.
Q14: In Java, how would you revoke serialization of attributes of a class?
Ans: Java makes easier to prevent member variables for being serialized using the non-serialized attribute. As a user, Java allows you to make an object non-serialized if that concerns security-sensitive information in the source code. Such non-serialized attributes can be applied to certain fields that contain sensitive information and unless a user doesn’t exclude these fields from serialization, the information will be accessible to any program with permission.
Q15: What’s your understanding and choice of IDE in Java?
Ans: An Integrated Development Environment or IDE allows Java (and/or other programming languages) developers to easily code as well as debug programs. It’s a collection of language-specific programming tools that offer various features such as code completion and syntax highlighting, accessible via a single interface. Codenvy, Eclipse and NetBeans are few of the go-to choices for Java developers that streamlines the process from scratch to delivery.
Understanding of the fundamentals, mastery of programming tools, as well having a well-structured answer to every Java interview question can help you nail the selection process for one of the high-paying jobs in the IT industry. However, don’t just limit your depth to only the 15 Java interview questions and answers for freshers we could add and keep on following Geekster Blog for more informative articles from the ever-exciting world of programming.
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