Introduction

Overview of Java

Java is a widely-used, platform-independent programming language known for its simplicity and power. As an object-oriented language similar to C++ and C#, it offers clear structure and code reusability. Its open-source nature, robust security, and extensive community support have secured its position as a leading programming language in the industry.

JVM, JRE, JDK

Note

Java bytecode is platform independent, but JVM and JRE are platform dependent, requiring specific implementations for each operating system.

Component	Description	Contains
JVM	Executes Java bytecode	- Java interpreter - JIT compiler - Garbage collector
JRE	Runs Java applications	- JVM - Core classes - Supporting files
JDK	Complete development package	- JRE - Development tools - Documentation

Run Java Program

Compile and Run

Compile the Java file using the javac command. Ensure the file name matches the public class name. Run the compiled program using the java command with the class name (without the .java extension).

javac HelloWorld.java
java HelloWorld

Alternative (Java 11 and later)

️Directly compile and run a Java file in one step using the java command:

java HelloWorld.java

This eliminates the need for a separate compilation step, making it convenient for quick testing and scripting.

Main Method

The main method is the entry point of a Java program. It must be declared as public, static, and return void. The method signature is:

public static void main(String[] args) {
    // Code goes here
}

- The args parameter is an array of strings that can be used to pass command-line arguments to the program. It is important to note that the length of this array can vary based on the number of arguments provided during execution. Additionally, if no arguments are provided, the length of the args array will be zero.