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Even when you have already finished college, you need to pass more exams to get the job of your dreams. To get a good position you need to face lots of Java developer interview questions. Which are even harder if you don’t have previous work experience.
Anyway, you can have some advantage if you prepare yourself for that interview. First, you have to know what areas of expertise the company you are trying to enter requires. Then, check these commonly asked questions to Java developers that we have compiled for you. Each organization has its own set of questions, but the ones we present here can be considered as general examples of the ones you need to answer properly.
Common Java developer interview questions
This part of the interview covers the basics of the Java programing, stating that the candidate has the capabilities that his CV claims.
What are the advantages of Java Programming Language?
- It is simple. Since Java syntax is based on C++, it is easier to learn if you already know that language.
- It is object–oriented. Actually is not fully object-oriented, but may be extent and works on an object-oriented paradigm.
- It is portable. It works on the principle of read-once-write anywhere approach, so it can be executed in any machine.
- It is platform independent. It doesn’t rely on the operating system to execute code. It comes with its own platform.
- It is secured. It doesn’t use pointers and has its own mechanism of handling memory management. It also uses the concept of Byte Code and Exception handling.
- It is robust. Using concepts such as automatic garbage collection, exception handling and other makes Java more robust.
- It can be distributed. It helps users to create distributed applications. We can call the methods from any machine on the internet.
- It is dynamic. In Java, classes are loaded on demand.
What is inheritance?
When a new class is derived from an existing class, inheritance is the means by which this process occurs. The new class inherits or acquires properties and methods of other classes, which is the same to say that a subclass takes the characteristics of a superclass or ancestor.
What is public static void main (String args[]).
This one of the basic things you have to memorize to code Java.
- public: access modifier, which specifies who can access the method, being accessible by any class.
- static: It marks a program as class-based, that can be accessed without creating the instance of a class.
- void: It defines the method’s return type, that won’t return any value.
- main: The name of the method. JVM search it as a starting point for an application with this particular signature.
- String args[]: The parameters that goes to the main method.
In Java, what is object cloning?
It is creating a copy of an object using the Clone() method. That creates a new instance of the object and initializes all fields.
What is the difference between sleep and wait in Java?
Both are used to pause a running thread. While sleep() gives a short pause, wait() will pause the execution until a given condition is fulfilled.
What is the size of int in a 64-bit Java Virtual Machine?
The size of an int variable is 32-bit. This is constant in Java, no matter the platform. Therefore, the size of primitive int in both 32-bit and 64-bit Java virtual machines is the same: it’s always 32 bits or 4 bytes.
What JRE, JDK, JVM and JIT stand for?
JRE means Java run-time environment and it’s mandatory to run Java applications. JDK is Java development kit, which provides tools to develop a Java program. JVM stands for Java virtual machine and it’s the process that runs Java application. JIT means Just In Time compilation: it helps to boost the Java application performance by converting Java byte code into native code at certain threshold.
Main technical questions
Keep in mind that companies are not looking for a perfect Java developer, but a person that will be doing day-to-day work. They can be looking for programming skills, Java-specific skills, library/toolkit experience, design skills or communication skills (if they are looking for a Java developer Manager). Be sure that you have the desirable skill set before applying to the position.
Describe the differences between vectors and arrays
In Java, vectors are dynamically allocated, contain dynamic lists of references to other objects and hold data from different data types. Therefore, vectors can change their as needed. On the other hand, arrays are static: they have fixed size and types.
Java has a garbage collection feature. Then, your program can never run out of memory?
Although the programming language has automatic garbage collection feature, if we create objects faster than the garbage collector can work, we will run out of memory. With the garbage collection it’s harder for a program to run out of memory, but it can still happen.
In Java, what is method overriding?
Method overriding is a run-time polymorphism. In any object-oriented language, it allows a subclass, derived class, extended class or child class to provide a different implementation of a method derived from its superclasses, base class or parent class. The subclass method needs to have the same name, signature and return type as the superclass method. Keep in mind that method overriding always requires inheritance.
Describe the use of the finalize() method
This method is called by the Java garbage collector when there are no references to an object. Actually, the finalize method of the Object class doesn’t do anything, but allows to override it to do clean up tasks like breaking I/O connections or dispose of system resources. Using the finalize() method is a good indication of efficient programming and clean code.
In Java, what’s the difference between path and classpath variables?
Both are environment variables, but the operating system uses path to find executables. Therefore, we always need to add the directory location in the path variable when installing Java or requires the OS to find the executable. Classpath is used by Java executables to locate class files.
What is harder to program, a synchronization code for 10 threads or 2 threads?
Synchronization code is independent of the number of threads, so writing code will have the same complexity in both cases. The difference lays on the choice of synchronization. If we need to handle a large number of threads, we must go for advanced synchronization technique like lock stripping.
Be prepared to write some code in order to solve a given problem, usually simple. You should be able to do it in a few lines and in a creative way.
Psychological questions for a Java developer interview
These questions are oriented to know if you can think like a programmer as well as interact with a development team. Most of the questions have not a single answer, but evaluates your wit and ability to think outside the box.
What will be your approach to solve (a problem)?
Must of the time the problem will be something directly related to the work the candidate will be doing for the company. You should be able to give a creative approach to the problem, breaking it down into parts, and anticipating the problems that may emerge from your methodology.
What would you do if you have to learn a new Java class?
This question measures your ability to learn about the job ahead, and the way you approach learning. You must have a good idea of what information you will need and where to find it: looking up tutorials, studying the documentation, consulting books, etc. Be sure to mention that you will need to learn things like class member variables, methods and constructors.
Questions to be a Java developer Manager
Some Java developers have the capability not only to interact with a team, but also to lead. If the organization is looking for a Java developer Manager, you might have to answer questions like the following.
What would you do if you received feedback on a task?
This question assess if you are good at following instructions and receiving feedback. It is an open-ended question, in which you must demonstrate that you are able to accept, understand and act accordingly on feedback. A good idea is to illustrate this skill with a past situation where you act on a feedback you received.
If you find a bug in a complex system, what would you do to fix it?
Any software developer can debug as one of his basic skills. But the right approach is to break down the problem rather than finding small errors in code snippets. If your answer contains the following key phrases, you will ace this question:
- Asking for help from other Java coders
- Breaking down the problem into smaller parts
- Checking the code for similar errors
- Expressing and testing assumptions
- Looking at stack traces
- Reproducing the error
- Turn problems into learning experiences
- Using a measured, scientific approach
- Writing tests to ensure that the bug does not returns
Describe the difference between unit, integration and functional testing
A unit test works on a single, isolated piece of code that is usually a method. The integration test ensures that your code integrates with other systems; while a functional test checks the actual functionality of an application, by using automated tools to simulate user interactions.
What you should check when reviewing a team member’s code?
Here you should demonstrate your analytical skills, knowledge of common mistakes and attention to detail. Then, you need to mention security flaws, system vulnerabilities, code functionality, readability and style, simplicity, resource optimization and code that fulfill regulatory requirements of the company.
A Java developer should be extremely passionate and committed to coding, but this programming language is one of the most wanted in the software market nowadays. So, if you prepare yourself properly and get the position you are looking for, the paycheck will compensate all the effort.
