The main() method, A First Java Program, Compiling and Executing

The main() method

• In Java, every application begins with a class name, and that class must match with filename.

• Filename: MyClass.java

Class:
public class MyClass {

}

• Every line of code that runs in Java must be inside a class. 
• For Example class MyClass
• A class should always start with an uppercase first letter.

• The main() method is mandatory.
• You will see the main() method in every Java program.
• For example:

public static void main(String[] args)

{
}

Any code inside the main() method will be executed. 

Inside the main() method, we can use the println() method to print a line of text to the screen.

Example: System.out.println("Hello World");

• Note: Every program must contain the main() method.
  Note: The curly braces {} marks the beginning and the end of a block of code.
  Note: Each code statement must end with a semicolon (;).

There are total three phases:
(1) Writing Program Phase

• Let's create java program which display string
• Step 01: Open Notepad or any Editor such as notepad++, Netbeans.
• Step 02: Write the following code.

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

• Step 03: Save the program as MyClass.java.

Note: Java program has .java extension to save program.

(2) Compiling Phase

• Step 01: Open Command Prompt (cmd.exe)
• Step 02: Navigate to the directory where you saved your file.
• Step 03: Type "javac MyClass.java" & generate bytecode with ".class" file.
  
  
  

Note: Javac compiler will compile your code. If there are no errors in the code, the command prompt will take you to the next line.

(3) Executing Phase
Step 01: Type "java MyClass" and it will display output as "Hello World".