Why is String[] args necessary in main() method in Java?

 

Why is String[] args necessary in main() method in Java?

In Java, the main method serves as the entry point for the program. The correct syntax for the main method is:

public static void main(String[] args) {
    System.out.println("Hello, Java!");
}

🔹 Breaking it down:

• public → Accessible from anywhere.
• static → No need to create an object of the class to run it.
• void → No return value.
• main → Special method recognized by the JVM as the starting point.
• String[] args → Stores command-line arguments (optional but required by JVM).

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Why Can't We Skip String[] args?

1. JVM looks for main(String[] args)

   • When you run a Java program, the JVM searches for the main method with exactly this signature:

     
     public static void main(String[] args)
     

   • If you change or remove String[] args, the JVM cannot find the correct main() method and throws a runtime error (NoSuchMethodError).

2. Java Specification Requires It

   • The Java Language Specification (JLS) defines that main must have String[] args, so removing it makes the method invalid for execution by JVM.

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What Happens if We Remove String[] args?

🚫 Code Without String[] args

public class Main {
    public static void main() {  // ❌ Wrong method signature
        System.out.println("Hello, Java!");
    }
}

🔴 Error at Runtime:

Error: Main method not found in class Main, please define the main method as:
   public static void main(String[] args)

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Can We Change the Parameter Type or Name?

✅ Changing Parameter Name

public class Main {
    public static void main(String[] myArgs) {
        System.out.println("Works fine!");
    }
}

✔ This Works because only the name changes, but the type (String[]) remains the same.

🚫 Changing Parameter Type

public class Main {
    public static void main(int[] args) {  // ❌ Wrong type
        System.out.println("This won't work!");
    }
}

🔴 Error at Runtime: JVM won't recognize this method as main().

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What is the Purpose of args?

Even though most programs don’t use args, it is useful for command-line arguments.

✅ Example: Passing Command-Line Arguments

public class Main {
    public static void main(String[] args) {
        System.out.println("First argument: " + args[0]);
    }
}

📌 Run with arguments:

java Main Hello

✅ Output:

First argument: Hello

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Conclusion

• String[] args is mandatory because the JVM requires this specific method signature.
• Removing or modifying String[] args causes a runtime error.
• It is used for command-line arguments, but even if unused, it must be present.

🚀 Tip: Even if you don't use args, always include it in main()!