Top 50 Java interview questions to hire and identify top talent

Java is one of the most popular coding languages, and it is used by developers to create back-end development projects. It is a versatile programming language that requires specific skills and expertise to navigate. Given the intricate design of the language, it becomes essential for organizations to identify and hire candidates with suitable skills and expertise in Java.

Ever since it was launched, Java has been one of the most popular coding languages preferred by developers everywhere. The increasing popularity of the coding language has also led to a surge in the number of developers in the job market. Understanding the basic concepts of Java and having certificates may not always indicate a skilled candidate, which is why it becomes crucial for recruiters to have a strong assessment process in place for recruiting highly skilled Java developers. Using online assessment tests and Java programming interview questions during the early stages of the recruitment process can help screen out unsuitable candidates, ensuring improved hiring outcomes.

1. What are applications and objects in Java?
2. How is an array list different from a vector?
3. How to override a static or private method in Java?
4. Explain what break and continue statements are.
5. What is a map in Java?
6. What is object cloning?
7. What are errors and exceptions in Java?
8. Are default parameter values supported in Java?
9. Define reflection and its uses.
10. Define marker interface.

Three sample answers to core Java interview questions

1. What are applications and objects in Java?

A candidate should know that Java applications are programs that developers create using the language, while Java objects are formed when the code is executed by an application.

2. How to override a static or private method in Java?

Candidates with an understanding of Java will know that it is not possible to override a static or private method.

3. Explain what break and continue statements are.

Break statements are used to terminate loops early based on certain conditions and pass control from the loop to the statement immediately after the loop. On the other hand, continue statements are used to skip the current loop iteration. After the current iteration is skipped, the next iteration begins immediately.

1. What is the ‘this’ keyword?
2. What is the ‘super’ keyword?
3. What is ‘method overloading’?
4. What is late binding?
5. Explain why the delete function works faster in linked lists as compared to arrays.
6. What is the difference between the ‘>>’ and ‘>>>’ operators?
7. What is the externalizable interface?
8. What is enumeration in Java?
9. Can codes run before you have executed the main method?
10. What types of constructors can be used in Java?

Three sample answers to intermediate Java interview questions

1. What is the ‘this’ keyword?

‘this’ is a reference keyword that is used to refer to the properties of the current class, like variables, constructors, instance, method, etc.

2. What is the ‘super’ keyword?

Candidates should be able to explain that ‘super’ is a reference keyword that refers to the immediate parent class object.

3. What is ‘method overloading’?

Method overloading is the process used to create method signatures using a single method. This can be done by changing the method’s return type or by varying the number of arguments.

1. Explain the use of multiple main methods in the same class.
2. What is the importance of bytecode in Java?
3. Explain the differences between compile-time polymorphism and runtime polymorphism.
4. Are global variables supported in Java?
5. Why is the main method static in Java?
6. Are sub-packages also imported when a package is imported?
7. How are abstract and final keywords different?
8. What are two-dimensional arrays?
9. What are the differences between a string, stringbuilder, and stringbuffer in Java?
10. What are garbage collectors and their disadvantages?

Three sample answers to Java interview questions for experienced professionals

1. Explain the use of multiple main methods in the same class

Multiple methods cannot be used in the same class as the main method is already a defined class. Any candidate with expertise in Java should be able to answer this question quickly.

2. What is the importance of bytecode in Java?

Bytecode offers portability and security for the Java programming language and executes a set of high-quality instructions. This also means that source code does not have to be recompiled for different applications and platforms.

3. Explain the differences between compile-time polymorphism and runtime polymorphism.

Candidates with experience in Java programming should know that in compile polymorphism, all the code is executed during compilation. With runtime polymorphism, code can be executed more flexibly, as it is compiled when the program runs efficiently.

1. What is the difference between an iterator and an iterable?
2. How is a list different from a set?
3. Explain the difference between a map and a list.
4. What is the difference between a stack and a queue?
5. How are the ‘Singly Linked List’ and the ‘Doubly Linked List’ different?
6. What is the difference between Failfast and Failsafe?
7. What is the difference between Queue and Deque?
8. What is the difference between TreeSet and HashSet?
9. What is the difference between PriorityQueue and TreeSet?
10. What are the differences between Lock, the ‘synchronized’ keyword, and Semaphore for managing thread synchronization?

Three sample answers to difference-based Java interview questions

1. What is the difference between an iterator and an iterable?

Candidates should explain that an iterator helps integrate over a collection of elements, while iterable is the way to iterate over a sequence of elements.

2. How is a list different from a set?

A list is an ordered collection which is accessed through an index. It allows for duplicates and can store multiple null elements. A set is an unordered collection that is accessed by hashcode and can only store a null element once.

3. Explain the difference between a map and a list.

A list maintains the order of insertion, allows duplicate values, and can store multiple null elements, while a map does not maintain the order of insertion, does not allow for duplicate values, and allows any number of null values but only a single null key at most.

1. How to handle errors while using try-catch blocks in the code?
2. What is the significance of Spring framework knowledge as a developer?
3. What will happen if the Math.random() method is used?
4. Execute a program in Java without using the main() method.
5. Give an example of a complex coding problem that the candidate was expected to solve in the past team.
6. Write a program using Java that uses the temporary variable to swap two numbers.
7. Explain the logic and steps for creating a Java program to show scroll up and scroll down.
8. Explain the four principles of object-oriented programming.
9. Write a Java program to find the third highest number in an array.
10. What is the difference between volatile and synchronized keywords in Java?

Three sample answers to skills-based Java interview questions

1. How to handle errors while using try-catch blocks in the code?

Such Java programming interview questions allow candidates to showcase their programming skills. They should be able to explain in detail what the try-catch method is and how the method works for catching errors.

2. What is the significance of Spring framework knowledge as a developer?

The Spring framework provides comprehensive infrastructural support and knowledge of this framework is essential for Java developers. Candidates should ideally cover the advantages offered by the framework, like how it enables developers to create secure and scalable applications and helps solve real-time problems.

3. What will happen if the Math.random() method is used?

Candidates should be able to explain how the Math.random() method enables them to generate double-type numbers in a pseudo-random manner. They should also cover the fact that the method can only generate numbers that range from 0.1 to 1.

Hiring decisions should be driven by data-backed insights and well-planned core Java interview questions that can help identify and hire top talent. Structured Java programming interview questions enable recruiters to gather unbiased insights into the abilities of candidates so they can reduce the time to hire and make informed hiring decisions.

Java programming interview questions should be integrated into the recruitment process after candidate screening. Pre-employment assessments can be administered first to screen out candidates who are unsuitable for the job role and help ensure that only the best candidates are cleared for the interview round.

Hiring managers can consider using pre-employment assessments that are relevant to the open position in the organization to evaluate candidates for their technical skills and knowledge, coding expertise, soft skills, cognitive abilities, and much more. Additionally, pre-employment assessments can also provide recruiters with deep insights into the candidates, which can ensure a suitable cultural fit and help curate a targeted set of core Java interview questions for different candidates.

Mercer | Mettl offers an expansive test library of scientifically validated, data-driven tests that hiring managers can use to effortlessly optimize and streamline the recruitment process. Explore Mercer | Mettl’s range of pre-employment assessments to choose the right set of tests that are relevant to the specific job role, the organization’s requirements, and the organization’s recruitment needs. Hiring managers can utilize specific, customizable Java developer assessment to evaluate technical and coding skills of candidates.

Enhance the recruitment process and reduce the risk of bad hires with the combination of the right recruitment practices, including pre-employment assessments and structured Java programming interview questions for experienced professionals as well as freshers.