learnJava

Lesson 0. Getting Started with Java: Hello World

1. Introduce yourself and tell us why you want to learn programming?

Please answer it on gist Java_01-1 if you have no github account, please create one right now.

2. Why Java?

What’s programming languages?
What’s different between Java and other languages?

Please do google research, look into at least 3 results. And answer the question base your understanding at gist Java_01-2

3. What you will learn from this class

Java foundation
Object Oriented Programming
Data Structure and Algorithm
Java Projects
AP CSA practice

4. Found out what is the latest version of Java and how to install it

download java open jdk from https://jdk.java.net/
setup java environment
- for windows https://www.w3schools.com/java/java_getstarted.asp
- for Mac guide to installling Java on MacOs

5 Install Java IDE (Integrated Development Environment)

VSCode
- Getting Started with Java in VSCode
- It’s our main java Editor
BlueJ
- We use it to create new Java project and Learn Object Oriented Programming with it
- BlueJ installation
- How to use blueJ
IntelliJ IDEA
Eclipse

6 HelloWorld Example

6.1 Hello World example in W3school

Hello World example in W3school (java get start sample)

6.2 Use BlueJ

Create and run Hello World program
Create a new Project in your IDE
Create a new Class with name “HelloWorld”
Add method to print string type variable
Compile your code
Create a instance of your Class “HelloWorld” with “ new HelloWorld()”
Run the code

6.2 Use VSCode

open the project folder with VSCode
VS Code set break point for debug

6.3 Command line Build and run the HelloWorld Sample 1

Crate a static main method in the HelloWorld Class

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

Run java file java HelloWorld.java
Build java file javac HelloWorld.java it will create a HelloWorld.java
Run builded java class file java HelloWorld
use jar simple jar cf HelloWorld.jar HelloWorld.class
java -cp HelloWorld.jar HelloWorld // run jar file with out manifest
use jar with Manifest file Place the MANIFEST.MF file in the META-INF directory within your project structure.

Most build tools (Maven,Gradle) automatically generate the manifest file with correct information. Configure your build script accordingly.
- Create MANIFEST.MF file
```
    //MANIFEST.MF 
    Manifest-Version: 1.0
    Main-Class: HelloWorld
```
- Make sure run Javac to build the java file before run jar command below jar cfm HelloWorld.jar MANIFEST.MF *.class
- Run Jar file java -jar HelloWorld.jar

6.4 HelloWorld Sample 2 (multiple files)

Source files Below files in folder sample2, also defined as package.

    //Hello.java
    package sample2;
    public class Hello {
        public void SayHello() {
        System.out.println("Hello: Hello World!");
        }
    }

    //main
    package sample2;
    import sample2.Hello;
    public class Main {

        public static void main(String[] args) {
            System.out.println("Main: Hello World!");

            //call hello in another java file
            Hello hello=new Hello();
            hello.SayHello();
        
        }

    }

    // ./META-INF/MANIFEST.MF
    Manifest-Version: 1.0
    Main-Class: sample2.Main

Run Java file

java Main.java
Build all java files, go to the parent folder javac Sample2/*.java

java -cp . sample2.Main
build with jar file

jar cfm sample2/HelloWorld.jar sample2/META-INF/MANIFEST.MF sample2/*.class
run the jar file java -jar sample2/HelloWorld.jar

7 Home Work

What’s the different of BlueJ from others Java IDEs? Put you answer as comments of gist Java_01-7
Try some AI tool to see how it could help you learn programming
- https://chatgpt.com/
- https://gemini.google.com/app
- https://www.perplexity.ai/ (Best AI tool for learning)
- https://arena.lmsys.org/ (compare results any two ai,choice sus-column-r for Grok2)

Code of this page https://github.com/stoneskin/learnJava/tree/main/00_HelloWorld