Thinking of starting a career in Java development? You’ve made a smart choice!
Even though it’s been around for years, Java remains a popular language finding new areas of application. From a strong community to adaptability, Java is one of the best languages that you could learn as a programmer.
Oh, and if that’s not enough motivation, the average salary of a Java developer currently stands at $100,302 per year.
Now that you’re probably even more pumped to get a new (or your first!) job as a Java developer, you should test your skills and see how well you can answer some of the most common Java interview questions. This way, you can find out which areas you need to brush up on to ace your interview.
So, without further ado, let’s get right into the questions!
- Basic Java Interview Questions for Refreshers
- Question 1: What do you understand abou Java?
- Question 2: What is the difference between Java and Python?
- Question 3: What are the major features of Java?
- Question 4: What is an object in Java?
- Question 5: What is the difference between StringBuilder and StringBuffer?
- Question 6: Differentiate between JDK, JRE, and JVM.
- Question 7: Define inheritance
- Question 8: What is the difference between overloading and overriding?
- Question 9: What is a class in Java?
- Question 10: Explain the creation of a thread-safe singleton in Java using double-checked locking.
- Intermediate Level Java Interview Questions
- Question 1: What is JDK? Mention the variants of JDK?
- Question 2: What are Access Specifiers in Java?
- Question 3: Can a constructor return a value?
- Question 4: Explain the keyword “this.”
- Question 5: Explain the keyword “super.”
- Question 6: Can we overload a static method in Java?
- Question 7: Define late binding.
- Question 8: Define dynamic method dispatch.
- Question 9: Why is the delete function faster in the linked list than an array?
- Advanced Java Interview Questions
- Question 1: Although inheritance is a popular OOPs concept, it is less advantageous than composition. Explain.
- Question 2: How is the creation of a String using new() different from that of a literal?
- Question 3: Is exceeding the memory limit possible in a program despite having a garbage collector?
- Question 4: Why is synchronization necessary? Explain with the help of a relevant example.
- Question 5: Is it possible to import the same class or package twice in Java and what happens to it during runtime?
- Question 6: Will the final block be executed if the code System.exit(0) is written at the end of the try block?
- Question 7: Explain the term “Double Brace Initialization.”
Basic Java Interview Questions for Refreshers
In this section, we’ll cover beginner-level questions for those who are just starting off with their career in Java programming.
Question 1: What do you understand about Java?
Java is a fast, high-level, and powerful object-oriented language that was developed in the 1990s. It can be widely used including such domains as game and application development.
Question 2: What is the difference between Java and Python?
Javais statistically typed and compiled whereas Python is dynamically typed. As a result, bugs can be identified and removed from Java more easily.
Question 3: What are the major features of Java?
Java is an object-oriented language which means that it involves classes and methods which define how an object will exist and interact with other elements.
It’s also platform-independent which means that the same code can be used on a number of platforms including Linux, Windows, Mac etc.
Since the language is also interpreted, an Interpreter reads bytecodes and executes them.
Another notable feature is strong memory-management and garbage collection which prevent memory from being used longer than it needs to.
Question 4: What is an object in Java?
Java objects consist of classes and methods that define how these objects will behave.
Question 5: What is the difference between StringBuilder and StringBuffer?
- StringBuffer is synchronized meaning that it’s only possible to call it by one thread at a time, making it less efficient.
- StringBuilder is not synchronized which means that it can be called by multiple threads simultaneously.
Question 6: Differentiate between JDK, JRE, and JVM.
- JVM is a virtual machine that is set up to allow Java apps to run on any platform.
- JRE is a packaged collection of libraries and classes that allow Java programs to run.
- JDK is platform-dependent and comprises development and debugging tools.
Question 7: Define inheritance
Inheritance is a mechanism through which a class can acquire the fields and methods of its parent class. It is only possible in situations where an “is-a” relationship exists between classes.
Question 8: What is the difference between overloading and overriding?
If two methods in the same class have the same name but different parameters, it’s called overloading.
If a method has the same name and parameters in both the parent and child class, it’s called overriding.
Question 9: What is a class in Java?
A class can be defined as the blueprint for objects with similar properties.
Question 10: Explain the creation of a thread-safe singleton in Java using double-checked locking.
This method ensures that the critical block of singleton instance code is locked, making the code more efficient.
Note: As a novice developer, if you learn Java online on codegym.cc, you can better prepare for these and more advanced questions as the platform facilitates hands-on experience.
Intermediate Level Java Interview Questions
Here are a few questions that you might be asked if you already have some experience with Java programming.
Question 1: What is JDK? Mention the variants of JDK?
JDK stands for Java Development Kit and comprises JRE and development tools that are used to create Java applications. A few different variants include:
- Standard Edition
- Enterprise Edition
- Micro Edition
Question 2: What are Access Specifiers in Java?
Access specifiers define how classes and methods can be viewed and used in Java. There are four types of access specifiers namely public, private, protected, and default.
Question 3: Can a constructor return a value?
Constructors return the reference of an object. Once you expect constructors to return a value in addition to this reference, they become a regular method.
Question 4: Explain the keyword “this.”
It’s used to refer to the current object of a method or to invoke a constructor.
Question 5: Explain the keyword “super.”
It’s used to refer to the immediate parent class of an object.
Question 6: Can we overload a static method in Java?
Yes, this is possible provided that the input parameters for the static methods are different.
Question 7: Define late binding.
Late binding refers to when the compiler leaves all argument and type checking of a method and this is all looked up at runtime.
Question 8: Define dynamic method dispatch.
This refers to when an overridden method is resolved at run time instead of being taken care of by the compiler.
Question 9: Why is the delete function faster in the linked list than an array?
This is because deletion in linked lists works by simply shifting pointer locations whereas deleting an element in an array would mean moving each element to fill in the newly emptied space.
Advanced Java Interview Questions
Here are a few advanced questions that you can encounter if you’re looking for a senior-level position as a Java developer.
Question 1: Although inheritance is a popular OOPs concept, it is less advantageous than composition. Explain.
Inheritance may be more popular but it still comes with certain limitations compared to composition. For instance, classes in Java can only come from one superclass which limits what a certain class can ‘inherit.’
Since composition is loosely coupled, it’s also easier to test functionalities and be more flexible with your code as opposed to inheritance.
Question 2: How is the creation of a String using new() different from that of a literal?
Using new() will result in the creation of a new string in heap memory whereas using literal syntax to create a string may result in an existing string being returned or a new string being created and made available in the string pool.
Question 3: Is exceeding the memory limit possible in a program despite having a garbage collector?
Yes, this is absolutely possible as certain objects may be out of reach of the garbage collector. Therefore, it’s important to dereference an object once you think its task is complete to prevent it from unnecessarily consuming memory.
Question 4: Why is synchronization necessary? Explain with the help of a relevant example.
Synchronization ensures that multiple threads are able to consume a shared resource efficiently and without affecting results. For instance, if you’re trying to read and write data in a file at the same time, the output may be affected.
Here, it would be best to let only one thread consume the resource at a time to avoid discrepancies.
Question 5: Is it possible to import the same class or package twice in Java and what happens to it during runtime?
The same package or class can be imported more than once, they will only be loaded once.
Question 6: Will the final block be executed if the code System.exit(0) is written at the end of the try block?
No, it will not be executed.
Question 7: Explain the term “Double Brace Initialization.”
Double brace initialization creates an additional anonymous class(inner braces) and provides an initializer for this secondary class as well.
Whether you’re a fresh graduate or have been programming in Java for years, it’s always best to test your skills and check how confident you can be at answering the most common interview questions based on your experience and expertise.
Remember, no matter how skilled you may be, always challenge yourself before any interview and give it your best shot.