main() Method in Java Interview Questions and Answers for 10 years experience

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100 Java main() Method Interview Questions

  1. What is the signature of the main method in Java?

    • Answer: The signature is `public static void main(String[] args)`. `public` means it's accessible from anywhere. `static` means it belongs to the class, not a specific object. `void` indicates it doesn't return a value. `String[] args` provides an array of command-line arguments.

  2. Why is the main method declared as `public`?

    • Answer: It needs to be `public` so the Java Virtual Machine (JVM) can access it from any class, regardless of package visibility.

  3. Why is the main method declared as `static`?

    • Answer: The JVM calls the `main` method before any objects of the class are created. `static` methods can be called directly using the class name, without needing an object instance.

  4. Why is the main method declared as `void`?

    • Answer: Traditionally, the `main` method doesn't need to return any value to the JVM. While technically you could have a return type, it's not standard practice and would be ignored by the JVM.

  5. What is the purpose of the `String[] args` parameter in the main method?

    • Answer: This array holds any command-line arguments passed to the program when it's executed. Each element in the array represents a single argument.

  6. Can the `main` method be overloaded in Java?

    • Answer: Yes, but only the method with the signature `public static void main(String[] args)` will be executed by the JVM.

  7. Can the main method be private?

    • Answer: No, it must be `public` for the JVM to access it.

  8. Can the main method be final?

    • Answer: Yes, it can be declared `final`, preventing it from being overridden in subclasses.

  9. Can the main method be abstract?

    • Answer: No, it cannot be abstract because it needs to provide a concrete implementation for the JVM to execute.

  10. Can the main method throw exceptions?

    • Answer: Yes, it can declare exceptions using a `throws` clause, but this is generally discouraged for the `main` method.

  11. How do you access command-line arguments within the main method?

    • Answer: You access them through the `args` array. For example, `args[0]` would be the first argument.

  12. What happens if no command-line arguments are provided?

    • Answer: The `args` array will have a length of 0.

  13. What is the role of the JVM in relation to the main method?

    • Answer: The JVM is responsible for loading the class containing the `main` method, creating an instance of the class (for non-static methods within main) and invoking the `main` method to start the program's execution.

  14. Explain the difference between `System.out.println()` and `System.err.println()`?

    • Answer: `System.out.println()` prints to the standard output stream (usually the console), while `System.err.println()` prints to the standard error stream (also usually the console, but can be redirected separately). `System.err` is typically used for error messages.

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