README.md

Update $JAVA_HOME on Ubuntu

• Check the available jdks

update-alternatives --config java

• Copy the selection path without /bin/java

/usr/lib/jvm/java-17-openjdk-amd64

• Edit the file

nano ~/.bashrc

• Add the following line

export JAVA_HOME=/usr/lib/jvm/java-17-openjdk-amd64

• Save the file (Ctrl + O, then Enter) and exit (Ctrl + X)
• Apply the changes by running

source ~/.bashrc

• Ensure that the JAVA_HOME variable is now set correctly by running

echo $JAVA_HOME

• It should output /usr/lib/jvm/java-17-openjdk-amd64

Installation on Windows

To install Java via the Windows Command Prompt, you'll need to download the Java Development Kit (JDK) and set it up. Here’s a step-by-step guide:

Step 1: Download the JDK

1. Go to OpenJDK page for a free version.
2. Choose the version you need and download the Windows installer (usually a .exe file).

Step 2: Install the JDK

1. Run the downloaded installer.
2. Follow the installation prompts. By default, it installs in C:\Program Files\Java\jdk-<version>.

Step 3: Set Environment Variables

1. Open Command Prompt: Press Win + R, type cmd, and hit Enter.
2. Set JAVA_HOME:
   • Type the following command (replace <version> with your installed JDK version):

     setx JAVA_HOME "C:\Program Files\Java\jdk-<version>"

3. Update the PATH Variable:
   • Add the JDK bin directory to your PATH by typing:

     setx PATH "%PATH%;%JAVA_HOME%\bin"

Step 4: Verify the Installation

1. Close the Command Prompt and reopen it to ensure the environment variables are updated.
2. Type the following command to check the Java installation:

   java -version

   You should see the installed version of Java.

Step 5: Test the Installation

You can create a simple Java program to test if everything works:

1. Open a text editor and write a simple Java program (e.g., HelloWorld.java):

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

2. Save it in a directory (e.g., C:\Java).
3. Open the Command Prompt, navigate to the directory, and compile the program:

   cd C:\Java
   javac HelloWorld.java

4. Run the program:

   java HelloWorld

If you see "Hello, World!" printed on the screen, you’ve successfully installed and set up Java!

Installation on MAC using Homebrew

To install Java 21 on a Mac using Homebrew, follow these steps:

Step 1: Install Homebrew (If Not Installed)

If you haven't already installed Homebrew, open Terminal and enter:

/bin/bash -c "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/HEAD/install.sh)"

Step 2: Install OpenJDK 21 with Homebrew

1. Open Terminal and run the following command to install OpenJDK 21:

   brew install openjdk@21

2. After the installation completes, Homebrew will display the path to the Java 21 installation, typically something like:

   /opt/homebrew/opt/openjdk@21
   

Step 3: Configure JAVA_HOME

To ensure that Java 21 is recognized as the default Java version, set the JAVA_HOME environment variable.

1. Add the following line to your shell profile file:

   • For Zsh (default on macOS Catalina and newer): edit ~/.zshrc.
   • For Bash: edit ~/.bash_profile or ~/.bashrc.

   export JAVA_HOME=/opt/homebrew/opt/openjdk@21
   export PATH="$JAVA_HOME/bin:$PATH"

   • Save the file (Ctrl + O, then Enter) and exit (Ctrl + X)

2. Reload the profile configuration by running:

   source ~/.zshrc  # or source ~/.bash_profile, depending on your shell

Step 4: Verify the Installation

Finally, confirm that Java 21 is installed and set as the default version:

java -version

You should see output like:

java version "21.0.x" 2023-09-19 LTS

Java 21 is now installed and configured on your Mac using Homebrew!