Top 20 Java Interview Questions And Answers for 2021

Java is one of the most popular languages in the field of IT. Many organizations use Java in various applications, and there is a high demand for a suitable candidate at Java. If you are a candidate who is preparing for a java interview, then this post is for you. Here, you will find the most important Java Interview Questions And Answers you must prepare before any job interview.

Java Interview Questions and Answers

Top 20 Java Interview Questions and Answers for 2021 1
Photo by Alex Green from Pexels

Q1. Why is the Java platform independent?

Since its byte codes will run on any device, regardless of the underlying operating system, Java is referred to as platform-independent.

Q2. What exactly do you mean by Java virtual machine?

A Java Virtual Machine is a virtual machine that allows a device to run a Java program. The JVM is a runtime engine that executes Java code and calls the main method. The Java Virtual Machine (JVM) is a computer system specification that must be implemented. JVM converts Java code to Bytecode, a computer-independent language that is identical to native code.

Q3. In Java, what are the various access specifiers?

Access specifiers are keywords in Java that are used to describe the method, class, or variable’s access scope. The four access specifiers in Java are listed below.

  • Public: The public classes, methods, and variables can be accessed by any other class or method.
  • Protected: Protected can be accessed by a class from the same package, a subclass of this class, or in the same class.
  • Default: When a class, method, or data member has no access modifier specified, it is said to have the default access modifier.
  • Private: The private class, methods, and variables can only be accessed from within the class.

Q4.In Java, describe public static void main(String args[])?

  • Public: It is an access modifier, Which specifies who can access this method. If the method has public as a specifier, then it can be accessible by any class.
  • Static: It is a keyword in Java that indicates that it is a class-based language. In Java, main() is made static to be accessed without having to create a Class instance. Since main() is called by the JVM before any objects are formed, and only static methods can be directly invoked by the class, the compiler will throw an error if the main is not rendered static.
  • Void: It is the method’s return form. The method Void is defined as one that does not return any value.
  • Main: It’s the name of the method that JVM looks for when it’s looking for a starting point for an application with a specific signature. It is the process in which the majority of the work is performed.
  • String args[]: It’s the value passed to the main method as a parameter.

Also Read: Machine Learning Using Python – A Novice Guide, 2021

Q5. What are the main theories of OOPs in Java?

OOP stands for Object-Oriented Programming. Object-oriented programming is about constructing structures that contain both data and methods, while procedural programming is about writing procedures or methods that perform operations on the data.

  • Classes and Objects: a class is a grouping of related objects. When we describe a class, all we get is a prototype or Skelton. As a result, when a class is made, no memory is created. Objects are the only things that take up memory.
  • Inheritance: The mechanism by which one class inherits the properties of another is known as inheritance.
  • Encapsulation: In Java, encapsulation is a method for encapsulating data and code into a single unit.
  • Abstraction: Abstraction is a technique for hiding implementation data from users and only provides them with functionality.
  • Polymorphism: A variable, method, or object’s ability to take several forms is known as polymorphism.

Q6. Why Java is not 100% Object-oriented?

Java isn’t entirely object-oriented since it uses eight primitive data types that aren’t objects: boolean, byte, char, int, float, double, long, and short.

Q7. In Java, what is garbage collection?

Garbage collection is a fully automatic operation in Java.Objects that are to be removed do not need to be marked directly by the programmer. The JVM is where garbage collection is applied. Each JVM is free to implement garbage collection in any way it sees fit, as long as it adheres to the JVM specification. 

Q8. What are the different features of Java Programming Language?

  • Simple: Java is a simple language to understand. Java’s syntax is based on C++, making it simpler to write programs in it.
  • Object-Oriented: The object-oriented paradigm in Java helps us maintain our code as a collection of various artifacts that include both data and behavior.
  • Portable: Java supports the read-once-write-anywhere method. On any computer, we can run the Java program. Java programs (.java) are translated to Bytecode (.class) that can run on any computer.
  • Platform Independent: Java is a cross-platform programming language. It varies from other programming languages such as C and C++, which require a platform to run. Java comes with its framework, which is used to run its code. The execution of Java is not based on the operating system.
  • Secured: Since it does not use explicit pointers, Java is stable. Java also has the Byte Code and Exception Handling concepts, making it more stable.
  • Robust: Java is a powerful programming language because it makes extensive use of memory management. It is more stable thanks to principles like automated garbage collection, exception management.
  • High Performance: Since Java bytecode is “similar” to native code, it is faster than other conventional interpreted programming languages. 
  • Multithreaded: By specifying multiple threads, we can write Java programs that manage multiple tasks at once. The critical benefit of multi-threading is that each thread does not take up memory. It has a shared memory space. Threads are essential for multimedia, Web applications, and other applications.
  • Dynamic: Java is a dynamic programming language. It allows classes to be loaded dynamically. It means that classes are loaded only when they are required. It also includes support for functions written in its native languages, C and C++.

Q9. What is an abstract class?

A class that cannot be instantiated is known as an abstract class. It is not possible to create an object with an abstract class, but it can be inherited. Only the Abstract method can be used in an abstract class. In an abstract class, Java only allows abstract methods, while other languages allow non-abstract methods.

Also Read: Top 30 Best Job Search Apps to Find You Dream Job in 2021

Q10. What is exception handling?

An exception is a condition that happens during the process of a program’s execution. Exceptions may be of any type, including runtime and error exceptions. Exception management methods such as the try, catch, and throw keywords are used to handle these exceptions properly.

public class Exception{  
  public static void main(String args[]){  
   try{  
      //code that may produce an exception  
      int data=100/0;  
   }catch(ArithmeticException e){System.out.println(e);}  
   //The program's remaining code
   System.out.println("The program's remaining code");  
  }  
}

Q11. In Java, what is a singleton class? 

A singleton class is one in which only one instance can be generated in a single JVM at any given time. By making the constructor private, we can make a singleton class.

Q12. Why are pointers not used in Java?

Pointers are not practiced in Java because they develop a program’s complexity. Because Java is known for its code simplicity, implementing the idea of pointers would be incongruent. JVM is responsible for implicit memory allocation; pointers are not used in Java to prevent direct memory access by the user.

Q13. What is the reason that multiple inheritances are not supported in Java?

Java only allows for multiple inheritances by interfaces. A class can perform as many interfaces as it needs, but it can only extend one other class. Multiple inheritances are not encouraged because it can result in a dangerous diamond issue.

Q14. What is the constructor?

The constructor is defined as a unique type of method which is used to initialize the state of an object. It is called during the class is instantiated, and memory for the object is allocated.

When the object is created with the help of a new keyword, the constructor of the class is called, which is the default constructor. The constructor must have a name that is identical to the class name.

Also Read: 8 Most Common Interview Questions For A Job Seeker

Q15. What are different types of inheritance?

Single Inheritance: 

A child and parent class relationship in which child class extends parent class are referred to as single inheritance.

Example:

Class a {
…
}
Class b extends class a {
…
}

Multilevel inheritance:

A child and parent class relationship in which a class extends the child class is referred to as multilevel inheritance. For example, Class A extends class B, while class B extends class C.

Example:

Class a {
….
}
Class b extends class a {
….
}
Class c extends class b {
… 
}

Hierarchical inheritance: 

When more than one class extends the same class, this is referred to as a child and parent class relationship. For example, Class B and Class C both extend class A.

Example:

Class a {
…
}

Q16. What are different types of polymorphism?

Static polymorphism: 

Static polymorphism is a polymorphism that is resolved during the compilation process. 

Dynamic polymorphism:

Dynamic polymorphism refers to a procedure in which a call to an overridden method is resolved at runtime rather than at compile time. It is also called Runtime polymorphism.

Q17. Why is String class considered immutable?

Since the String class is immutable, a String object can’t be changed once it’s been created. Since String is immutable, it can be securely spread across many threads, which is critical for multithreaded programming.

Q18. What Is the Difference Between = = and equals() ?

 The Equals() method is used to evaluate the equality of two objects described by business logic. 

== compares primitives and objects using the == or equality operator.

Q19. How do you use the ‘this’ keyword?

We can use ‘this keyword to point to a current object; We can also invoke the current class constructor or current class method, we can pass it as an argument into our constructors or methods.

Q20. What is the difference between Overloading and Overriding?

Overloading occurs when two methods of the same name but different properties are present. On the other hand, overriding refers to a condition in which two methods of the same name and properties appear in a parent and child class, respectively.

This takes us to the end of the blog on some of the most important Java Interview Questions And Answers. We hope you could benefit from the same and are now well-versed in the top java interview questions and answers. Happy Learning!

Must Read: What You Need to Understand About High Converting Landing Page Design

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.

%d bloggers like this: