Practicing These Top 20 Interview Questions and Answers on Java Will Guarantee Your First Job

Need to quickly recapitulate a few common Java interview questions? Continue reading this blog where we have gathered 20 commonly asked interview questions and answers on Javafor freshers.

No, these aren’t random interview questions and answers on Java that we gathered from the internet. Instead, we reached out to top interviewers tasked with hiring only the top-notch professionals in the coding industry, and asked them what set of questions they usually ask freshers to test out their knowledge on Java. Here’s what they gave us:

Ques-1: Briefly explain your understanding of Java?

Answer: Java is an object-oriented high-level programming language developed by Sun Microsystems. What makes Java unique is its platform-independent nature that enables cross-platform compatibility across different platforms.

Ques-2: What are the common features of Java that makes it unique?

Answer: Some of the features that make Java unique are its object-oriented programming environment, platform independency, high performance with the Just in Time (JIT) compiler, and multi-threaded execution of processes.

Ques-3: Briefly explain your understanding about Java Virtual Machine.

Answer: Java Virtual Machine or JVM is an abstract specification machine that offers runtime environment in which Java bytecodes are directly executed. This implementation is also known as the Java Runtime Environment or JRE.

Ques-4: What is the full form of IDE and what does it serve?

Answer: An Integrated Development Environment or IDE allows developers to easily code and debug programs. It’s a collection of programming tools that provide various features such as code completion and syntax highlighting.

Ques-5: Briefly explain how the serialization of attributes of a class is revoked in Java?

Answer: Java prevents member variables from being serialized using the non-serialized attribute. As a programmer, Java allows you to make an object non-serialized if it concerns security-sensitive data in the primary source code.

Ques-6: What are default constructors in Java.

Answer: In Java, default constructors are the no-argument constructors that initialize instance variables. In JRE, such constructors will be created automatically by default if any other constructor isn’t already defined by the developer.

Ques-7: Explain abstract classes in Java and how it’s created.

Answer: An abstract class can have both an “abstract” and a “non-abstract” method which are a concrete class. Java lets programmers create an abstract class by using the “abstract” keyword before the class name with a semicolon.

Ques-8: What is the fundamental difference between an Array and an Array List?

Answer: In an Array, size should always be given while declaration where specifying the index is mandatory to put an object. Whereas in an Array List, the size changes dynamically, therefore no index is required to be specified.

Ques-9: What is the difference between String, String Buffer and String Builder?

Answer: Strings are stored on constant string pool in which the previous value cannot be changed once the reference changes. Whereas String Buffer is synchronized and String Builder is not threader, and therefore, not synchronized.

Ques-10: Briefly explain public and private access specifiers.

Answer: Public members are visible on Class A and Class B (same packages) as well as Class C (outside packages). In contrast, private members are only visible in the same class, and not for other classes in the same of other packages.

Ques-11: What is the primary difference between HashMap and HashTable?

Answer: In a HashMap, methods are not synchronized and allows only one null key and multiple null values. On the other hand, in HashTable, key methods are synchronized where null keys are not allowed ensuring thread safety.

Ques-12: Define Collections in Java.

Answer: Collection is a framework that is developed to store objects, manipulate the design to store in objects, and are used to perform important Java functions such as Searching, Sorting, Manipulation, Insertion and Deletion.

Ques-13: Explain the fundamental difference between abstract class and interface.

Answer: Abstract classes have a default constructor containing abstract as well as non-abstract methods. The class which extends an it shouldn’t need implementation of every method, but only the required ones in the sub-class. Whereas, an interface does not have any constructor and only requires the abstract method to me declared. Classes that implement the interface should provide the implementation for every method and contains only the constants.

Ques-14: How would define Ordered and Sorted in Collections?

Answer: Ordered means the values which are stored in a particular collection is entirely based on the values which are added to the collection. Whereas, in Sorted, sorting mechanisms can be applied internally as well as externally. Sorting is executed in JVM memory once the data is being read from the database using the comparator. Efficiency depends on the size of the Collection and Ordered is sorted by specifying the order-by clause during the retrieval.

Ques-15: What is your understanding of Copy constructor in Java?

Answer: Copy constructor is used when programmers need to initialize the value to the new specified object from the old object inn the same class. Although, we are initializing new object, this can also be done with object cloning.

Ques-16: Define a Comparator in Java.

Answer: Comparator is an interface in Java containing the compare method. By overloading the compare method, developers can define how the values must be compared, which is not possible with the collections.sort() method.

Ques-17: What’s your statement on the fact that static and private method overriding is possible in Java?

Answer: This statement is false since static methods have zero relevance with objects. In the case of any child class, a static method of the parent class with the exact signature can exist without even outputting any compilation error.

Ques-18: Define the different ways of thread usage.

Answer: In Java, a thread can be defined and implemented in two primary ways; Implementing Runnable Interface and Extending Thread class. However Runnable Interface is more advantageous and therefore more preferrable.

Ques-19: What will the output if the static modifier isn’t included in the main method signature?

Answer: Although there wouldn’t be a compilation error instantly being output by the IDE, but since the program is run, JVM cannot map the main method signature and the code will output “NoSuchMethodError” at the runtime.

Ques-20: Can you make the main() thread a daemon thread?

Answer: What’s unique about Java multithreading is that the main() threads are always non-daemon threads. And therefore, it’s no possible to change the nature of a main() thread from a non-daemon thread to a daemon thread.

Over 20 years of gradual improvisations summed up in only 20 questions? Never! Java is so versatile that it’s near impossible to master it in a lifetime. But that shouldn’t stop you from keep learning and we suggest this excellent blog from Geekster on 15 Interview Questions on Java for Freshers where each and every answer is detail-oriented. While you are at it,

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