Install Java on Ubuntu

To install Java and run Java code in Linux (Ubuntu or other distributions), follow these steps:

Step 1: Install Java

Option 1: Install OpenJDK (Recommended)

Check Available Java Versions

sudo apt update
apt search openjdk

Install OpenJDK 17 (Recommended)

sudo apt install -y openjdk-17-jdk

To install a different version (e.g., Java 21), replace openjdk-17-jdk with openjdk-21-jdk.

Verify Java Installation

java -version
javac -version

Option 2: Install Oracle JDK (If Required)

Oracle JDK requires manual installation. Use this if OpenJDK is not suitable for your needs.

1. Download Oracle JDK from the official Oracle website.
2. Extract it and set up environment variables manually.

Step 2: Run Java Code

Method 1: Compile and Run Java Code (Without an IDE)

1. Create a Java file:
   SH

   nano HelloWorld.java
   

2. Add the following Java code:
   JAVA

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

3. Save the file (Ctrl + X, then Y, then Enter).
4. Compile the Java file:
   SH

   javac HelloWorld.java
   

   This generates a HelloWorld.class file.
5. Run the Java program:
   SH

   java HelloWorld
   

   Expected output:
   TEXT

   Hello, World!
   

Method 2: Run Java Code Using jshell (Interactive Mode)

If you installed Java 9+, you can use jshell for quick testing:

jshell

Then type:

System.out.println("Hello, World!");

Press Enter, and it will print:

Hello, World!

Exit jshell using:

/exit

Step 3: Set JAVA_HOME (If Needed)

To set the JAVA_HOME environment variable:

echo "export JAVA_HOME=$(dirname $(dirname $(readlink -f $(which java))))" >> ~/.bashrc
echo "export PATH=\$JAVA_HOME/bin:\$PATH" >> ~/.bashrc
source ~/.bashrc

Check if it’s set:

echo $JAVA_HOME