Answers to 14 Frequently Asked Java Interview Questions (2023)

Have you scheduled a Java interview for your ideal position? Here are some Java interview questions and solutions to help you succeed.

James Gosling invested in Java, a high-level language that adheres to object-oriented programming paradigms, in 1982. It is among the most well-liked and often employed programming languages. Both novice and experienced software engineers choose it as a prospective job.

Java is all about classes, inheritance, abstract classes, JSON, iterators, enumerations, volatile variables, transient variables, hibernate, and HTTP tunneling. The syntax is derived from the C++ and C programming languages. But it’s crucial to be aware of the key inquiries interviewers could make.

Here are some key interview questions and responses to assist Java developers.

Java: Is it purely object-oriented? Justify your response.

Java isn’t purely object-oriented, though. It supports primitive data types that aren’t objects, such short, byte, double, float, long, char, boolean, etc. The majority of the object-oriented requirements are nevertheless met.

Why is Java so well-liked as a platform-neutral language?

Due to the compiler and runtime environment (JRE), the Java programming language is independent of all software and hardware. The code is quickly compiled by the Java compiler and turned into platform-independent byte code. As a result of the code’s ability to operate on several platforms, it is quite well-liked.

Why are JDK, JRE, and JVM fundamentally different from one another?

Java Development KitJava Runtime EnvironmentJava Virtual Machine
The tool needed to describe, assemble, and package Java programs is called JDK.JRE is used to execute Java bytecode.        The Java Virtual Machine (JVM) is an abstract machine that offers a run-time setting to facilitate the execution of Java bytecode.      
JRE and a development tool are included.This makes the JVM implementation more reachable and enables its physical existence.             Implementation, specification, and runtime instances are all included in the JVM.  
It uses Java platforms in their standard, micro, and enterprise editions.It has a number of files and libraries, which makes using JVM simpler.It executes code, verifies input, and loads.

Give a brief overview of Java class access specifiers?

The access specifier in Java is a term that is used before a class name. It indicates the access scope by utilizing several types:

  • Protected – This prevents access from any other class to fields or methods from the same class and the same package (sub-classes or where they belong).
  • Private – This gives you access to the fields and methods of the class to which they belong.
  • Public – Throughout the code, it is simple to access the method, class, and field.
  • Default – A class, field, and method may only be accessed within the same package; they cannot be accessed from another package or from outside.

What exactly do you mean by local and instance variables?

Local variables are variables that are accessible exclusively within the constructor, function, or block in which they are found. A local variable is used to implement the block scope limitation. The local variable that is declared inside the method will not be accessible to or known by the other class method.

All methods have access to these class-wide variables, which can be defined within or outside of methods, using an instance variable. Object attributes may be seen through the variables. In the event of any update, just the instance is impacted, not the instances of the other classes.

What does JIT Compiler mean?

By using a Just In Time Compiler, bytecode may be quickly and efficiently compiled while improving application performance. It also aids in converting JVM code to CPU instruction set.

What is the singleton class?

It is a distinct class type that only renders one instance or object at once.

What does object cloning mean?

Object cloning is the process of making a duplicate Java object to aid developers in implementing it later. The clone () function can be used to implement java.lang by Java programmers.interface that is simple to copy.

Why constructors?

Code snippets known as constructors are used to create objects having the same name as classes. The object is also automatically generated and lacks a return type. It features two different types of constructors, including:

  • Constructor with parameters – The constructor can utilize the supplied values to initialize instance variables that accept arguments.
  • Default constructor: it generates no argument contractors by default, initializes the instance variables, and does not accept any inputs. There isn’t a specified constructor otherwise.

What is the distinction between Java’s == and equals ()?

The binary operator used to compare objects and primitives in the Java programming language is the equality operator (==). Public boolean equals (Object o) is the method provided by the Object class. Equals () checks for equality between two objects while also defining the Java class for objects according to business logic.

What are the differences between HashSet and TreeSet ?

Maintain the order of the elements.The order of the elements is not preserved.
Enables the use of a diverse item.Allows no heterogeneous objects.
Uses trees to implement the SortedSet interface and store data.Uses a hash table to implement.

What is Double Brace Initialization?

Double Brace Initialization is a Java technique that combines two distinct operations. To establish an anonymous inner class and an initialization block, respectively, double brace initialization requires two braces. The « this » pointer enables the inner class to use the outer class in a single statement for both initialization and creation.

The Java String Pool definition

A new object is produced after sorting the collection of Strings in heap memory, which is known as the Java String Pool. The objects are checked for availability by String Pool, and the same reference is then returned to the variables. In the absence of it, a new object is created with a return to the relevant references.

Collection Class in Java: what does it mean?

Think of it as the architecture for the framework that enables manipulation and object classification. Tasks like deletion, searching, modification, sorting, editing, and adding are made easier by the collection, which also includes frameworks like Methods, Classes, and Interfaces.


Java, with its amazing standard libraries and potent tools, is unquestionably one of the most widely used high-level programming languages. For a variety of concerns, including concurrency-based ones, it provides threading functionality. It also combines stability to the product with built-in features and simple syntax.

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