14 Frequently Asked Java Interview Questions and Answers [2023]

Do you have a Java interview lined up for your dream job? Here are the Java interview questions and answers that can help you ace the interview.

In 1982, James Gosling invested a high-level language Java that follows the principles of object-oriented programming. It is one of the most popular and widely used programming languages. Beginners and professional software developers opt for it as a potential career choice.

Java is about class, inheritance, JSON, iterator, enumeration, volatile variables, transient, hibernate, HTTP tunneling, and abstract class. It derives the syntax from C++ and C programming languages. However, it is essential to know the vital questions that interviewers may ask.

To help the Java developers, here are some of the important interview questions and answers.

Is Java a pure object-oriented language? Explain your answer.

No, Java is not a pure object-oriented language. It supports primitive data types such as short, byte, double, float, long, char, boolean, etc. which are not objects. However, it satisfies many of the object-oriented aspects.

Java programming language doesn’t depend on any software and hardware due to the compiler with the runtime environment (JRE). Java compiler compiles the code instantly and converts it to byte code (platform-independent). Due to this, the code can run on multiple systems making it extremely popular.

Explain the basic difference between JDK, JRE, and JVM.

Java Development Kit Java Runtime Environment Java Virtual Machine
JDK is the tool that is required to document, compile, and package Java programs. The Java bytecode is executed using JRE. JVM is an abstract machine that provides a run-time environment to make it easy to execute the Java bytecode.
It comes with a development tool and JRE. With this, the JVM implementation is more accessible and can exist physically. JVM includes implementation, specification, and runtime instances.
It implements standard edition, micro edition, and enterprise edition Java platforms. It contains several files and libraries, making it easier to use JVM. It performs code execution, verification, and loads.
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Give a glimpse into access specifiers for Java classes?

The keyword that one use before a class name is the access specifier in Java. It denotes access scope using different types:

  • Protected – This accesses fields or methods from the same class and the same package (sub-classes or where they belong) but not from any other class.
  • Private – This accesses the fields or methods from the same class and from where they belong.
  • Public – The method, class, and field is accessed easily throughout the code.
  • Default – One can access class, field, and method from the same package, not from the native package or from outside.

What do you mean by a local variable and an instance variable?

Local variable – These variables are available within a constructor, function, or block that one can access only inside them. The block scope restriction is applied in a local variable. The other class method won’t be able to access or have knowledge of the local variable declared inside the method.

Instance variable – All the methods can access these variables in the class declared inside and outside the methods. The variables glimpse into the object properties. Only the instance is impacted without affecting all other class instances in case of any modification.

What is JIT Compiler?

Just In Time Compiler is used to enhance the application’s performance that compiled bytecode, reducing time consumption. It also helps translate the code from JVM to the CPU instructing set.

Explain singleton class in one line.

It is a unique class type rending one instance or object at a time.

What is object cloning?

Object cloning means creating a clone copy of Java objects, helping developers implement it later. Java developers can use the clone() method to implement java.lang.Cloneable interface easily.

Explain constructors.

Constructors are blocks of code that can initialize an object with the same name as a class. Along with it, the object is created automatically and has no return type. It has two kinds of constructors such as:

  • Parameterized Constructor – The constructor can initialize the instance variables that take the arguments and uses the provided values.
  • Default Constructor – The constructor initializes the instance variables, creates no argument contractors by default, and does not take any inputs. No other constructor is defined.

What is the difference between == and equals() in Java?

The equality operator (==) is the binary operator that compares objects and primitives in the Java programming language. The Object class provides the method as public boolean equals(Object o). At the same time, equals() check the equality of two objects and define the Objects class in Java defined by business logic.

Differentiate between TreeSet and HashSet.

TreeSet HashSet
Maintain elements in sorted order. Elements are not maintained in sorted order.
Permits a heterogeneous object. Does not permit a heterogeneous object.
Implements SortedSet Interface using trees for data storage. Implements through a hash table.

Explain Double Brace Initialization.

In Java, Double Brace Initialization combines two independent processes. Double Brace Initialization uses two braces to create an anonymous inner class and initialization block, respectively. “This” pointer helps the inner class to refer to the outer class for both initialization and creation in a single statement.

Define Java String Pool.

The collection of Strings is known as Java String Pool sorting in heap memory, where a new object is created. String Pool checks the availability of the objects, and then the same reference is returned to the variables. Otherwise, a new object is made with the return to the respective references.

What does collection class in Java mean?

Consider it as architecture representing the framework that helps manipulate and sort the group of objects. The collection helps perform tasks like deletion, searching, manipulation, sorting, editing, inserting, etc., including frameworks like Methods, Classes, and Interfaces.

Final Words

Undoubtedly, Java is one of the most popular, high-level programming languages with impressive standard libraries and powerful tools. It offers threading support for several problems, such as concurrency-based issues. It also has built-in features and easy-to-use syntax combining stability to the product.

To master Java, consider enrolling in one of these online Java courses.

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