Writing, Compiling & Running Simple Java Program

1. Writing a Simple Java Program

Java program likhne ke liye pahla step ek class banana hai. Java me har program me kam se kam ek class hona zaroori hai. Yahan ek simple "HelloWorld" program diya gaya hai jo console me "Hello, World!" print karta hai:

// File name: HelloWorld.java
public class HelloWorld {
    public static void main(String[] args) {
        System.out.println("Hello, World!");
    }
}

    

Important points:

• public class HelloWorld se class declare hoti hai, jiska naam file ke naam se match karna chahiye.
• main method se program start hota hai.
• System.out.println() console par message print karta hai.

2. Compiling the Program

Java code ko run karne ke liye pahle ise compile karna hota hai. Compilation source code (Java file) ko bytecode (.class file) me convert karta hai. Yeh step terminal ya command prompt me hota hai.

Steps to compile:

• Terminal (command prompt) kholen.
• Jis folder me HelloWorld.java file saved hai, us folder me navigate karein using cd command.
• Command type kare:
  javac HelloWorld.java
• Agar koi errors nahi hain, to compiler koi output nahi deta, lekin HelloWorld.class file create ho jayegi.

3. Running the Program

Compile hone ke baad program ko run karna hota hai. Run karne ka matlab Java Virtual Machine (JVM) ko bytecode execute karna hota hai.

Steps to run:

• Command prompt ya terminal me ye command type karein:
  java HelloWorld
• Output me dikhai dega: Hello, World!

4. Important Notes

• Java file ka naam .java extension ke saath hona chahiye aur public class ka naam usi file ke naam se match karna chahiye.
• Compile karne ke baad .class file generate hoti hai jisme bytecode hota hai.
• Run command me .class extension nahi lagate, sirf class ka naam likhte hain.
• Agar multiple files hain, to unhe sahi classpath ke sath proper order me compile karna hota hai.