25 Java Beginner Level Interview Questions & Answers
Below is a list of our Java Beginner Level interview questions. Click on any interview question to view our answer advice and answer examples. You may view 5 answer examples before our paywall loads. Afterwards, you'll be asked to upgrade to view the rest of our answers.
1. How would you define abstraction in terms of Java programming?
In this question, your job is to utilize your understanding of abstraction in terms of Java programming. Try to define abstraction and give a real-world example of how you would use it in a Java program. No code is needed in this question. In other words, just try to express your understanding in terms of applications or programs where you utilized abstraction.
Abstraction in Java is one of the main object-oriented programming concepts that Java utilizes to keep a clear difference between the common and more specific classes. To explain, during the process of defining the main feature of an application or Java program, most of the time we face a type of class known as abstract classes. These classes are used to define the common features and attributes of a more general class.
During one of my Java projects, I worked on an application that was used to manage a human resources system. This system had a class called Employee that was defined as an abstract class that served thereafter as a parent class for other subclasses such as MarketingManager, FinancialAnalyst, and SoftwareDeveloper classes.
Written by Mohamed Echout on April 19th, 2021
2. How would you override the toString() method in Java?
This question will require you to write a code example that demonstrates the toString method in a Java class.
The goal here is to showcase your understanding of the @Overrride notation and your coding level when it comes to defining a method body.
public class DemoClass{
private int age ;
@Override
public String toString() {
return return "The age is: " + " " + age ;
}
}
Written by Mohamed Echout on April 19th, 2021
3. How would you formulate a try-catch block in Java?
This question will require you to write a code example that demonstrates the utilization of try-catch to deal with exceptions and Java errors.
Your job is to write a code example demonstrating the use case of try catch in a simple yet effective way. One approach is to write a trycatch for an out of bound array error.
public class DemoMain {
public static void main(String[ ] args) {
try {
int[] myLevels = {10, 20, 30};
System.out.println(myLevels [10]);
} catch (Exception e) {
System.out.println("Array out of index.");
}
}Written by Mohamed Echout on April 19th, 2021
4. How would you read a file in Java?
This question will require you to write a code example that demonstrates the utilization of file input-output using a Java class.
Try to explain your answer by describing your example then make sure to write a clear and concise code block.
Avoid any complicated code blocks and make sure to limit your code to the lowest possible number of lines.
In this code example, I will read a file using the Scanner class. First will start by importing both the file and scanner library.
Next, I will create two objects the first is called textFile which will take as input the file name then a second object that will be used to read my file. Finally, I will implement a loop that will read my file line by line.
import java.io.File;
import java.util.Scanner;
public class ReadFileDemo{
public static void main(String[] args){
File textFile = new File("file.txt");
Scanner scFile = new Scanner(textFile);
while (scFile.hasNextLine())
System.out.println(scFile.nextLine());
}
}Written by Mohamed Echout on April 19th, 2021
5. What are the main functionalities of packages in a Java program?
In this question, you will be required to explain the use case of Java packages. Your answer can include a code example if needed, but you might keep your answer limited to an example of use cases combined with your experience working with Java packages.
Try to avoid generic definitions and make it clear that you are insightful about the benefits of packages and how they can help in Java modularity.
Packages are used in Java to classify your classes based on different divisions, features, and functionalities of your program.
For example, a Java program will contain a package containing the main classes of your program including the various features of your application. In addition, you might also have a package containing your test classes to test the functionalities of your classes and method implementation.
Written by Mohamed Echout on April 19th, 2021
6. How would you utilize getters and setters in a Java class?
This question will require you to write a code example that demonstrates the utilization of getters and setters using a Java class.
Try to write your code block to answer the question in the simplest way possible. One example is to write a class with one attribute and define the getter and setters for that class.
Short and correct code is always better than long, verbose and buggy code.
public class AgeClass {
private int age;
public int getAge() {
return this.age;
}
public void setAge(int age) {
this.age= age;
}
}Written by Mohamed Echout on April 19th, 2021
7. How would you create a Java class?
This question will require you to write a code example that demonstrates the creation of a Java class.
Avoid any complicated code blocks that will require debugging and double-checking your code. In other words, try to write your Java class in the simplest way possible. Indeed, this is not a question to showcase long code blocks and complex class creation.
public class DemoClass{
private int num;
DemoClass(int num){
this.num = num;
}
} Written by Mohamed Echout on April 19th, 2021
8. Provide a code example of inheritance in Java programming?
This question will require you to write a code example that demonstrates the utilization of inheritance using a Java class.
Try to lay the basis of your answer by describing your code.
Avoid any Java statements that will require importing third-party libraries. In other words, try to write your code block to answer the question in the simplest way possible.
In this example, I will define two classes. First, a Teacher class that doesn't contain any attributes or methods. Second, a Programming Teacher class that extends the first class.
class Teacher {
}
public class ProgrammingTeacher extends Teacher{
}
}Written by Mohamed Echout on April 19th, 2021
9. Provide a code example of abstraction in Java programming?
This question will require you to write a code example that demonstrates the utilization of abstraction using a Java class.
Try to lay the groundwork of your answer by explaining your example then make sure to write a clear and concise code block.
Avoid any complicated code blocks that will require debugging and double-checking your code. In other words, try to write your code block to answer the question in the simplest way possible.
Indeed, this is not a question to showcase long code blocks and complicated function calls. Keep it simple and to the point.
The idea of abstraction in Java can be demonstrated using an abstract class. For example, a human resources management system programmed in Java would take into account different types of employees.
To explain, this program will have an abstract class called Employee, and this class with content the main features and methods that are common amongst all employees in the system.
Also, this class opens the door for subclasses that can present a more specific version of an Employee such as a SalesPerson who is considered an employee but contains more features such as commission rate for instance. The following is the code block demonstrating this use case:
public abstract class Employee {
private String firstName;
private String lastName;
private int salary;
public Employee(String firstName, String lastName, int salary) {
this.firstName= firstName;
this.lastName= lastName;
this.salary= salary;
}
}
public class SalesPerson extends Employee {
private double commission;
public SalesPerson(String firstName, String lastName, int salary, double commission) {
super(firstName, lastName, salary);
this.commission= commission;
}
}Written by Mohamed Echout on April 19th, 2021
10. How would you create an ArrayList that will hold a list of String variables?
This question will require you to write a code example that demonstrates the utilization of an ArrayList using a Java class.
Try to lay the foundation of your answer by explaining your example of how an Arraylist would be used. Avoid any complicated code blocks that will require importing more libraries and using methods that are not mandatory for your example.
Keep in mind that the interviewer is aware that you don't have access to the Java documentation or the help of a search engine so keep your code simple and to the point.
To create an ArrayList in a Java program we will first have to import the ArrayList library found in the java.util package.
Next, we create an array list object using the Arraylist constructor that takes as an argument the datatype of our ArrayList elements. The following is a code example demonstrating this concept:
import java.util.ArrayList:
public class Main {
public static void main(String[] args) {
ArrayList<String> names = new ArrayList<String>();
}
}Written by Mohamed Echout on April 19th, 2021
11. While defining an integer attribute what is the difference between using the keyword int and Integer?
In this question, you need to make sure that you explain the difference between primitive data types found in procedural programming languages and wrapper classes found in Java in terms of usability and benefits that they bring to a Java program.
No need to provide any code example at this stage. In other words, provide a clear difference between a normal int and Integer class and give an example of their use cases.
Java programming allows the programmer to define integer variables using two techniques. First, using the typical operator called int.
This operator allows the creation of a primitive integer attribute. Second, using the Integer wrapper class not only allows the creation of integer attributes but also comes with a set of methods that can be used to conduct some operation on this variable.
The clear distinction between using an int and Integer is that the first will result in the creation of an integer variable and the second will result in the creation of an object of type Integer.
Written by Mohamed Echout on April 19th, 2021
12. What is the mechanism used in Java to implement access modifiers?
This is one of the questions that you will get early on in the interview process. Indeed, this question is used to understand if you have good experience working with access modifiers in terms of Java.
The way to answer this question is to explain how access modifiers are useful in a Java program and what are the main benefits they bring in terms of object-oriented best practices.
Java uses access modifiers to limit the scope by which attributes, methods, and classes can be accessed. These access modifiers can be sorted from the highest level of accessibility to the lowest.
First, the public access level enables total freedom of accessing attributes, classes, or methods. Next, the protected access modifier is limiting the access of all Java fields to the package level.
Besides, the protected access modifier enables access to child classes that inherit all Java fields of the parent class. The following access level is the default access modifier that only allows access in the level of a Java package. The lowest level of accessibility in Java is the private level that only allows access to attributes and methods within the same class.
Written by Mohamed Echout on April 19th, 2021
13. How would you define polymorphism in terms of Java programming?
This question will be asked as part of a series of questions target to understand how comfortable you are with the major object-oriented programming concepts in terms of Java programming.
No need to produce any code examples. Focus on defining polymorphism in terms of Java programming and try to avoid long-winded examples. Being precise at this stage is considered a great asset to not only showcase that you have a good grasp of polymorphism but also that you used it in your previous Java programs. In other words, be very informative and to the point.
Java brings a very flexible workflow to every program developed with its language. For instance, polymorphism is one of the main features that allow Java program to be very portable and extensible.
To explain, polymorphism allows the programmer to call a method based on its signature and use cases. In other words, your methods cab take many forms based on the method call.
For example, a Java program can have a set of methods with identical names but different arguments and logic. This feature allows your Java program to not only use the method name as an indicator of which method to call but also the method arguments. Indeed, allows you to call the same method in different stages of your program but with different expected behavior based on the argument specified in the method.
Written by Mohamed Echout on April 19th, 2021
14. Why would Java be considered an object-oriented programming language?
This is what is known in programming interviews as a conversation starter. In other words, this question is used to open up the conversation about Java programming and its fundamentals.
Do not go into the details of Java syntax or the philosophy behind object-oriented programming. In other words, keep it simple and direct because other more advanced questions will be coming up in the conversation when your knowledge can be showcased.
Java programming is considered object-oriented because it takes into account the idea that everything in a program can be represented as a class.
To explain, during the creation of a program using Java, we make sure that every part of our program is an object. In other words, these objects will be created using classes that are representing the main attributes and methods of these objects. This logic of having your program represented as a set of classes, objects, methods, and attributes is followed in the creation of a Java program which makes Java an object-oriented programming language.
Written by Mohamed Echout on April 19th, 2021
15. How would you define encapsulation in terms of Java programming?
This question will be asked later on in the interview process to understand how comfortable you are with the fundamentals of Java object-oriented concepts. No need to provide code examples for this question just define the term and present an example or use case of encapsulation. The best strategy for these kinds of questions is to be selective with your words and try to explain the encapsulation concept in a compiled manner.
The concept of encapsulation is applied to enforce the best practice of object-oriented programming. As a starting point, two rules should be respected for encapsulation to be incorporated into your Java program. First, all attributes inside your class should be set to a private access level. Second, your classes should include two types of methods, getters, and setters. These methods will be then used to set up your attributes. Based on this example encapsulation is defined as limiting the access to your attributes to getters and setters. In other words, the attributes are encapsulated in your class and can only be accessed with your getters and setters.
Written by Mohamed Echout on April 19th, 2021
16. How would you define inheritance in terms of Java programming?
This is considered a more advanced question that is used to understand your level of proficiency in Java programming. Avoid giving code examples in this question. In other words, give a good definition of inheritance in terms of Java and be ready for a follow-up question about a code example.
Java programming provides programmers with the ability to expand the usability of a Java class. To expand, your program can have an initial class that can be thereafter inherited by other classes. For example, your Java program can have a Vehicle class that can be inherited to a Car class. The difference between the two classes is that the Car class is a more specific kind of Vehicle. To extend the functionalities of the class Vehicle we can use the inheritance mechanism of Java by utilizing the keyword extends.
Written by Mohamed Echout on April 19th, 2021
17. How would you use a constructor to initialize a Java object?
This question is open-ended which means you need to either explain in your own words how to utilize a constructor or provide a code example. The strategy that is risk-free in this question is to combine both. Start your answer with a small introduction then follow up with a code example of how to utilize a constructor to initialize a Java object.
To initialize a Java object a constructor can be used to define the attributes that this object will take. For example, let's say our goal is to initialize an object called obj. This object doesn't have any attributes that need initialization. Also, the object can be initialized using a class called DemoClass. This example can be demonstrated as follows:
public class Main {
public static void main(String[] args) {
DemoClass obj = new DemoClass();
}
} Written by Mohamed Echout on April 19th, 2021
18. What is the main functionality of a Java class constructor?
In this question, your job is to showcase your understanding of the Java programming workflow. In other words, link your answer to the concepts of object-oriented programming by explaining the main reason behind using a constructor and its functionality. Avoid going into unrelated details such as the difference between object-oriented and procedural programming languages. In other words, keep your answer brief yet informative and expect a follow-up question about code examples demonstrating the use case of constructors.
The main functionality of a class constructor is to initialize your objects in your Java program. To explain, during the creation of a Java program the first step is to create a set of classes that are a layout of your main features and functionalities. Next, these classes should be initialized and created using a method called a constructor. Finally, the constructor will take as an argument the initial values that will be assigned to your object variables.
Written by Mohamed Echout on April 19th, 2021
19. What is the main functionality of every component in the Java main method?
Normally this is a follow-up question to the main code example question. In this stage, your job is to simplify every component in the main method. In other words, define and develop every element including the return type, access level, and method arguments. Try not to neglect any element while answering this question. This will show the interviewer your ability to explain in detail a simple code statement and your level of understanding in terms of basic Java concepts.
The main method encapsulates all the needed elements of a Java method. To explain, these elements can be defined as follows:
public: Java uses access modifiers to define the scope by which class, attributes, and method can be accessible. The main method is set as a public method as it has to be easily accessible by the Java Runtime Environment.
static: Because the main method is the first function that will be called in a Java program, this method should be static to enable your java program to easily allocate memory for this method with no need for object instantiation.
void: One of the main elements of a method signature in Java is the return type of a method. The main method in Java doesn't return any value which means the return type of main in this case will be set to void.
String[] args: To run a Java program we can use the command line or an IDE. In case we are using the command line we can specify a list of arguments that the main method can take. In our case, the main method in Java takes as arguments an array of String values called args.
Written by Mohamed Echout on April 19th, 2021
20. How do you define the starting point of your Java program known as the main method?
In this question, your job would be simply to provide a code example of the main method. In other words, you can for sure try to start your answer with a small introduction about the main method and what makes it very important to the flow of your Java program. However, the end goal is to write down the syntax of the main method. Expect a follow-up question that will test your understanding of every element in the main method.
In Java programming, the main method is the starting point of every program and it is the first method executed when you run a Java program. The syntax of the main method can be as coded as follows:
public class MainMethod {
public static void main(String[] args) {
}
} Written by Mohamed Echout on April 19th, 2021
21. How do you handle errors in your Java program?
This question examines your understanding of the try-catch block a very important element of Java programming. To answer this question you can define a situation or a scenario where Java errors can be handled. Another approach you can take is to simply explain the flow of your program in case of an error and the way your program would behave with a try-catch code block implemented. Expect a follow-up question about the syntax of a try-catch or a code example of how to implement this error handling code block.
Java is a very robust programming language when it comes to handling errors. To explain, Java provides a programming mechanism known as try-catch that can be used to process your code blocks and trigger an action that will be there after execution in the catch block. This code block enables you to follow the flow of your program and test every block before execution. The logic of a try-catch is simply to execute some code in the try block and in case of error your Java program will jump to the catch block to recover from this error.
Written by Mohamed Echout on April 19th, 2021
22. What are the object-oriented features supported by the Java programming language?
In this question, you will need to bring to the table some of the main object-oriented programming concepts that you used in your Java programming development journey. In other words, try to bring some of the main object-oriented programming features that the Java programming language supports and back up your answer with some examples to show your high level of understanding. Don't worry about covering all the concepts just make sure that when you cover any one of the concepts that you are doing it with clarity and precision in mind.
The java programming language supports all the major object-oriented programming concepts and features. To explain, these programming language provides a clear and intuitive way of implementing inheritance, abstraction, polymorphism, and encapsulation. For example, the Java programming langue enables you to create an abstract class using the abstract keyword. Additionally, you can easily inherent or share some features and functionalities of your classes using the extends keyword. Indeed, Java brings to the table a very intuitive set of keywords and methods that enable the full use of all the major object-oriented programming concepts.
Written by Mohamed Echout on April 19th, 2021
23. Can an application developed in Java run on all the major operating systems?
In this question, you will have to show the interviewer that you understand Java from an architectural level. To explain, try to bring the conversation on how Java code compiles and why it is considered portable and platform-independent in the first place.
Any program or software developed using the Java programming language will be compiled and converted to bytecode. This code enables Java to be platform-independent and can run in all major operating systems with no issues at all. To explain, the only prerequisite tool to run any Java program is to have the Java Virtual Machine (JVM) installed and configured in your operating system.
Written by Mohamed Echout on April 19th, 2021
24. What are the main prerequisites to run Java code on your machine or system?
In this question, the interviewer is trying to understand your level of knowledge in terms of the Java environments and the tools needed to start working with the programming language. You can be as general or as specific as you want the most important thing is to shed some light on the different tools you used to work with Java. Also, explain any packages or tools you have installed to get up and running with Java.
To get up and running with Java you will have to install the Java Development Kit or what is also known as JDK. This tool kit contains an all-in-one implementation of the needed tools and libraries needed to get up and running with the Java code. Also, an IDE or integrated development environment would be needed to created classes and test your code. One of the most used IDEs that I am familiar with is Eclipse an open-source tool that contains all features needed to start programming with Java.
Written by Mohamed Echout on April 19th, 2021
25. What is the difference between a class and an object in terms of Java programming?
This question examines your understanding of the basic building blocks of the Java programming language. You can be as general or as specific as you want. The most important takeaway is to define both terms (object vs class). Try to give examples and an initial definition to describe these terms.
A class is a blueprint that contains all the methods, attributes, and logic of your program written to create a set of objects. For example, a class can be considered the blueprint of a house and the object is the house after construction and building work. Objects are created based on the initial class defined in your Java program.
Written by Mohamed Echout on April 19th, 2021