Commonly Asked Java Interview Questions
Java is one of the most popular programming languages, it’s been in use for around 30 years, and is used by thousands of companies. Java’s popularity has made it one of the highest-paid programming languages because the salary offered for skilled java developers is much better than the average salaries of other developers.
With that being said, there are a lot of developers out there who are trying to secure a decent job using Java as their primary skill.
And to help these freshers who want to become successful Java developers, we have compiled a list of commonly asked Java interview questions. These questions are asked in the interviews with almost every company.
Java interview questions
Java software engineers are in high demand which makes this a great time to be a Java developer and this article features the most common Java interview questions and answers.
1. Define Java in the simplest way.
Java is an object-orientated, high-level general-purpose programming language and computing platform first released by Sun Microsystems in 1995. Java was designed with a mission: Write Once, Run Anywhere (WORA). This means that code written in the Java programming language can run on all platforms that support Java without the need to rewrite the code.
The Java programming language is now used on a wide variety of devices including PCs, tablets, smartphones & ovens. You’ve seen it in your fridge, you’ve seen it at the gas station, and even in your car’s navigation system.
2. Differentiate between JDK, JRE, and JVM.
Java Development Kit, popularly abbreviated as JDK, it’s a collection of software tools from Oracle Corporation required for developers to develop and run Java programs.
JRE stands for Java Runtime Environment, it’s bundled inside JDK. The Java runtime environment is used to run the Java programs on a computer. It’s for end-user, it’s not used for the development process.
The JVM, or Java Virtual Machine, is a tool for running Java programs. It is an abstracted computer runtime environment that executes your Java code line-by-line. JVM is also called an interpreter.
3. Explain wrapper classes in Java.
Wrapper classes in Java are classes whose objects wrap primitive data types. It means a primitive value can be wrapped into a wrapper class.
Wrapper classes have become increasingly popular in Java because they allow greater reusability.
4. Explain how Java is a platform-independent language.
Java is a programming language that can run on any operating system and in any environment. So, you don’t need to recompile the code for another operating system or any other different environment. This makes it platform-independent and hence, it runs with ease on Windows, Linux, Unix, Mac OS, etc.
Java can be used to create a platform-independent application that you can use on any of these platforms without worrying about the type of operating system.
5. Name some well-known Java IDEs.
Some of the popular Java IDEs are:
- Eclipse
- IntelliJ IDEA
- NetBeans
- BlueJ
- JDeveloper
Here’s an article where you can know about Java IDEs in detail.
6. What is method overriding in Java?
Method overriding is a mechanism of Java, where a derived class has the ability to override methods of its base class. A derived class can provide its own definition for an inherited method, thereby extending the behavior of the method defined in the base class. This can be done as a replacement or just as an addition to the original method, depending on how it’s done and why.
7. What is Object-Oriented Programming?
In computer science, object-oriented programming (OOP) is a programming paradigm that views computations as the manipulation of abstractions of information called objects.
In object-oriented development, programmers design software by creating abstractions of real-world objects. The definition of an object is specified in terms of its properties and behaviors. For example, a “book” object may be defined by its title, author, subject matter, release year, and color.
It’s important to note that Java is not an object-oriented language. It does not have classes or inheritance like in object-oriented languages like C++.
8. Explain garbage collection in Java?
In Java, garbage collection is a mechanism to reclaim memory by automatically freeing up memory that has been allocated but not yet used.
Garbage collection occurs when there are no longer any references to allocated objects, and therefore no more memory needs to be allocated for them and they can be freed up by the system. The JVM is expected to run out of space eventually if there are no intervening system events or if applications continue to allocate additional memory.
Garbage collection is important in Java because it’s one way you can reclaim memory that you don’t need anymore. If you’re not careful about your use of memory, you can easily exhaust the available heap space
9. Explain the OutOfMemoryError in Java.
The OutOfMemoryError is thrown when a Java application runs out of memory and there should be enough free memory to process the request. However, in certain situations, your Java application might not be able to create new objects or allocate storage space for them and this can result in the OutOfMemoryError.
An OutOfMemoryError is usually caused by an out-of-control allocation activity by your Java application.
10. What are the differences between Java and C++?
There are thousands of programming languages, many with different features and purposes. C++ is a powerful, flexible, and advanced language but it can sometimes be harder to learn than other languages, such as Java.
Although C++ has been around longer than Java, it has a reputation for being harder to learn. This is because C++ has a more intricate structure and syntax.
Some ways Java and C++ are different are:
- One variable type: Java uses one type of variable while C++ uses two — char and int. You can’t mix these types in your programs.
- First-class functions: Functions are defined in the same way as variables in Java but they also can be assigned to objects like classes in C++.
- Allocation: The way you allocate memory is different between Java and C++. In Java, you allocate memory on the stack while in C++ you allocate on the heap.
Related: How to Think Like a Programmer
Final words
Whether you are a beginner or an expert, these questions will help you get a better understanding of what to expect during your next job interview.
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Originally published at https://blog.nextstacks.com on February 5, 2022.
