First Hello Java Program

MS March 19, 2023

 First Hello Java Program

The "Hello, World!" program is a simple program that displays the message "Hello, World!" on the screen. It's often used as a first example when learning a new programming language or environment.

Here's the Java code for the "Hello, World!" program:

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

Let's break down each line of this code:

  • public class HelloWorld: This line defines a public class named HelloWorld. In Java, every program must have at least one class, and the name of the file containing the code must match the name of the class (in this case, HelloWorld.java).
  • public static void main(String[] args): This line defines the main method of the program. The main method is the entry point of a Java program, and it's where the program begins executing. This line also declares that the main method takes an array of strings as a parameter (String[] args).
  • System.out.println("Hello, World!");: This line uses the System.out object to print the message "Hello, World!" to the console. The println method adds a newline character after the message, so that the next line of output appears on a new line.

To run the "Hello, World!" program, you'll need to:

  1. Save the code to a file named HelloWorld.java.
  2. Open a command prompt or terminal window and navigate to the directory containing the HelloWorld.java file.
  3. Compile the program by running the command javac HelloWorld.java. This will create a file named HelloWorld.class in the same directory.
  4. Run the program by running the command java HelloWorld. This will execute the program and display the message "Hello, World!" in the console.

 compilation flow of the "Hello, World!" Java program:

  1. Source Code: First, you need to write the Java code for the "Hello, World!" program in a text editor or an integrated development environment (IDE). The code should be saved in a file with a .java extension, with the name of the file matching the name of the public class defined in the code (in this case, HelloWorld.java).

  2. Compilation: The next step is to compile the Java source code using the javac command. The javac command takes the name of the Java source file as an argument, and it generates a binary file with a .class extension that contains the bytecode for the program. In this case, you would run the command javac HelloWorld.java to compile the "Hello, World!" program.

  3. Bytecode Generation: During the compilation process, the Java compiler generates bytecode for the program. Bytecode is a low-level, platform-independent representation of the Java code that can be executed by the Java Virtual Machine (JVM).

  4. Bytecode Verification: Once the bytecode is generated, the Java Virtual Machine (JVM) verifies the bytecode to ensure that it is safe to execute. The JVM checks the bytecode for various security violations, such as accessing private data or executing unsafe code.

  5. Execution: Finally, the JVM executes the bytecode for the "Hello, World!" program. The java command is used to execute the program, and it takes the name of the public class containing the main method as an argument. In this case, you would run the command java HelloWorld to execute the "Hello, World!" program. When executed, the program displays the message "Hello, World!" on the console.

Parameters used in First Hello Java Program

The "Hello, World!" Java program uses the following parameters:

  1. public: This is an access modifier that specifies that the class HelloWorld can be accessed from anywhere in the program. The public keyword makes the class visible to other classes and packages.

  2. class: This is a keyword that is used to define a new class in Java. In this case, the class is named HelloWorld.

  3. HelloWorld: This is the name of the class that is being defined. The name of the class must match the name of the source code file.

  4. main: This is the name of the method that serves as the entry point for the Java program. The main method is the first method that is called when the program is executed.

  5. String[] args: This is the parameter list for the main method. The String[] indicates that the args parameter is an array of strings. The args parameter can be used to pass command-line arguments to the program.

  6. System.out.println(): This is a method that is used to print a string to the console. The println() method adds a new line character after the string, so that the next line of output appears on a new line. In this case, the string being printed is "Hello, World!".

The public class HelloWorld line defines the class HelloWorld, which contains the main method. The main method is where the program starts executing, and it calls the System.out.println() method to print the "Hello, World!" string to the console. The String[] args parameter is not used in this program, but it is included in the main method signature to allow the program to accept command-line arguments if needed.

 

 

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