Top 20 Cognizant Java Interview Questions and Answers

Top 20 Cognizant Java Interview Questions and Answers. Are you an aspiring Java developer and looking for make a career at Cognizant? Hi candidate!!! below we have listed down some Cognizant Java Interview Questions and Answers. These are collected from the students who have faced the Interviews they have shared through social media like YouTube and Linkedin. So drive to top Java Interview Questions and Answers.

Mastering Your Cognizant Java Interview

Q. Is Java Platform Independent? How?

A: Yes Java is a complete platform independent language as we know. This means that Java code can run on any device that has a Java Virtual Machine (JVM) installed. Here below is how it works in a machine.
The Java compiler as we know as javac which converts Java source code into bytecode which will stored in as .class files.
=> Whereas Bytecode is not associated with any specific hardware or operating system. As it is designed to execute by the JVM.
=> Also the JVM which is totally platform dependent interprets and runs the bytecode on any operating system (OS).
=> This above architecture allows Java programs to write once and then run anywhere that making the Java platform as independent.

Q. What are the Top Features of Java?

A: Java is one of the most popular programming languages for the below reasons:

Simple: The Java syntax is straight forward and easy to identify and learn.
Platform Independent: In any device with JVM we can run the Java programs within any hardware and software.
Interpreted and Compiled: Java is both interpreted by the JVM and compiled to bytecode.
Robust: Features like garbage collection and exception handling make Java a very reliable language.
Object Oriented: Java uses objects and classes promoting reusability and modularity.
Secure: Java applications can be shared without exposing the source code that enhancing security of the code.
High Performance: Java is faster than other traditional interpreted languages. So thanks to the optimization of JVM.
Dynamic: Java supports dynamic loading of classes and interfaces.
Distributed: Java enables distributed computing with its built in networking capability.
Multithreaded: Java can handle multiple tasks continuously with its multi threading capability.
Architecture Neutral: Java bytecode is not dependent on the machine architecture.

Q. What is JVM?

A: The JVM or Java Virtual Machine is a very vital part of the Java platform. It loads verifies and executes Java bytecode. While the JVM itself is platform dependent (operating system OS) it allows Java programs to be platform independent and that execute the same bytecode on any system.

Q. What is JIT?

A: JIT stands for Just In Time compiler a part of the Java Runtime Environment (JRE). It enhance the performance of Java applications by:

Compiling source code with the Javac compiler into bytecode.
Passing bytecode to the JVM.
Converting bytecode into native machine code at runtime.
Executing the compile code directly improving speed and performance.
The JIT compiler activates when a method is called compiling it into machine code that make the faster execution.

Q. What are the Memory Storages in JVM?

A: There are many JVM memory areas for efficient execution of Java programs:

Class (Method) Area: Stores class level data like runtime constants, fields, and method code.
Heap Memory: Allocates memory for objects created during runtime.
Stack: Stores data and partial results needed for method execution and dynamic linking.
Program Counter Register: Keeps track of the address of the current JVM instruction.
Native Method Stack: Contains all native methods used in the application.

In these above ways we can execute faster runtime for any application in Java program.

Q. What is a Classloader in Java?

A: A classloader is a part of the Java Runtime Environment (JRE). It dynamically load Java class and interface into the JVM execution. This means the Java runtime system does not need to know about the file system or the location of files.

Q. Difference between JVM JRE and JDK in Java Program

A: JVM (Java Virtual Machine): An interpreter that convert bytecode into machine code. It is a platform dependent but execute platform independent bytecode.
JRE (Java Runtime Environment): An installation package providing an environment to run Java application including the JVM and other library.
JDK (Java Development Kit): A development package that include the JRE and tool needed to develop Java application.

Q. Explain public static void main(String[] args) in Java

A: In Java the main method is defined as public static void main(String[] args). In below each term is mentioned:

public: An access modifier making the method accessible globally.
static: Allows the method to be called without creating an instance of the class.
void: Indicates the method does not return any value.
main: The entry point of the application.
String[] args: An array of command line arguments passed to the program.

Q. What is the Java String Pool?

A: The Java String Pool is a kind of special memory area in the heap where a string literal is stored. When a new string value is created, the JVM checks the pool. If the string already exists the existing reference is used. Else a new string value is added to the pool.

Q. What Happens if We Dont Declare the Main Method as Static?

A: If the main method is not declared as static, the Java Virtual Machine (JVM) will not recognize it as the entry point of the application, and the program will not run.

Q. What are packages in Java?

A: Package in Java is collection of related class and interfac. Package helps us in Java programe as below section.
Prevent name conflicts.
Controlling access to classes and interfaces.
Organizing the entire code for better maintainability and easy to readability.

Q. Advantages of Using Packages in Java

A: Avoid Name Clash: It Prevents naming conflicts in java code.
Access Control: Leverage the control access to all classes and interfaces.
Hidden Classes: It always allows us for the class creation which we can not access outside of the package.
Easy Location: Simplify the whole process of locating and using related classes.

Q. Types of Packages in Java

A: User Define Package: Created by the user to group related classes and interfaces.
Built In Packages: Provided by the Java API such as java.util or java.lang.

Q. Different Data Types in Java

A: Java has two main categories for data types:

Primitive Data Type: Simple data type that store only single value.
boolean: true or false
byte: 8 bit signed integer (int)
char: 16 bit Unicode character (char)
short: 16 bit signed integer (int)
int: 32 bit signed integer (int)
long: 64 bit signed integer (int)
float: 32 bit floating point (float)
double: 64 bit floating point (float)
Non Primitive Data Type: Reference types that store memory addresses of object.
Strings
Arrays
Objects
Classes
Interfaces

Q. When to use the Byte Data Type?

A: The byte data type is a 8 bit signed integer that contains the values ranging from -128 to 127. It is used when memory saving are important and it is required to store the range of values that fits within this limit.

Q. Can We use Declare Pointers in Java?

A: No Java can not support pointers. This design choice enhances security and simplicity. For reducing the risk of memory leaks and pointer related errors java does not support declare pinters.

Q. Default Values of Data Types in Java

A: byte: 0
float: 0.0f
double: 0.0d

Q. What is the Default Value of the byte Data Type in Java?

A: The default value of the byte data type in Java is 0.