Why Am I Getting a 'Main Method Not Found' Error in Java?

Understanding the "Error: Main Method Not Found" Message in Java

Introduction

When executing Java programs via the command line using the java command, such as java MyClass arg1 arg2, the Java Virtual Machine (JVM) searches for a specific entry point known as the main method within the nominated class. If this method is not defined or fails to meet certain requirements, an error is triggered.

Causes and Requirements

The main method serves as the application's entry point and is crucial for the JVM to launch the program. It must adhere to specific requirements:

1. Location: The main method must reside within the specified class.
2. Name: The method's name must be "main" (case-sensitive).
3. Visibility: The method must be declared as public.
4. Modifier: The method must be static.
5. Return Type: The method must return void.
6. Parameters: The method must have a single argument of type String[], which collects command-line arguments.

Error Message Variations

Depending on the Java tool used, different error messages may be encountered if the main method is missing or does not meet the criteria:

• "Error: Main method not found in class MyClass, please define the main method as: public static void main(String[] args)"
• "Error: Main method not found in the file, please define the main method as: public static void main(String[] args)"
• "Error: Main method is not static in class MyClass, please define the main method as: public static void main(String[] args)"
• "Error: Main method must return a value of type void in class MyClass, please define the main method as: public static void main(String[] args)"
• "java.lang.NoSuchMethodError: main"

Resolution

To address this error, verify the following:

• Ensure a main method exists in the specified class.
• Confirm the main method name is correctly spelt as "main" and is not modified with special characters.
• Check that the main method is declared as public.
• Ensure the main method is declared as static.
• Verify that the main method returns void.
• Confirm that the main method takes a single String[] argument for command-line arguments.

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