Consequences of Non-Static main() Method in Java

In Java What happens when the main() isn't declared as static?

In Java, the main() method serves as the entry point for any standalone Java application. The standard signature for the main() method is:

public static void main(String[] args)

If the main() method is not declared as static, the Java Virtual Machine (JVM) will not be able to invoke it directly without creating an instance of the class. Here’s what happens in that case:

1. Error on Execution: If you try to run a Java program where the main() method is not static, you will encounter a runtime error. The JVM looks for the main() method with the exact signature, and if it doesn't find it, it will throw an error.

2. Example: Consider the following code:

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

   If you try to run this class, you will get an error similar to:

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

3. Instance Method: If you declare main() as an instance method (non-static), you would need to create an instance of the class to call it. However, this is not how Java applications are typically structured, and it defeats the purpose of having a designated entry point.

4. Conclusion: Always declare the main() method as static to ensure that the JVM can call it without needing to instantiate the class. This is a fundamental requirement for Java applications to run correctly.