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

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Step 1: Install Java

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Check Available Java Versions

sudo apt update
apt search openjdk

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

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Verify Java Installation

java -version
javac -version

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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.

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Step 2: Run Java Code

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

  1. Create a Java file: 
    nano HelloWorld.java
  2. Add the following Java code: 
    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: 
    javac HelloWorld.java
    This generates a HelloWorld.class file.
  5. Run the Java program: 
    java HelloWorld
    Expected output: 
    Hello, World!

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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

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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