How do I install and manage multiple Java versions with SDKMAN?

SDKMAN (Software Development Kit Manager) is a command-line tool that allows you to manage multiple versions of Java and other SDKs easily. Here’s how you can install and manage multiple Java versions using SDKMAN:

Step 1: Install SDKMAN

Open your terminal.
Run the following command to install SDKMAN:
```
curl -s "https://get.sdkman.io" | bash
```
Follow the instructions provided during the installation process, which might ask you to update your shell configuration.

Reload your terminal or execute:

source "$HOME/.sdkman/bin/sdkman-init.sh"

Verify the installation:
```
sdk version
```
If installed correctly, it will display the version of SDKMAN you just installed.

Step 2: List Available Java Versions

To list all available Java versions:

sdk list java

This will display a list of Java distributions and their versions.

Step 3: Install a Specific Java Version

To install a desired Java version, use the following command:

sdk install java <version>

For example, to install OpenJDK 21:

sdk install java 21-open

Once installed, it will set this version as the default one automatically.

Step 4: Use a Specific Version

To see all installed versions, use:
```
sdk list java
```
To switch to a specific version:
```
sdk use java <version>
```
For example:
```
sdk use java 17-open
```
This will only apply to your current terminal session.

Step 5: Set a Default Version

To make a specific Java version the default across all terminal sessions:

sdk default java <version>

For instance:

sdk default java 21-open

Step 6: Check Active Java Version

To check the currently active Java version:

java -version

Managing Installed Versions

To see installed versions:
```
sdk list java
```
To uninstall an old or unused version:
```
sdk uninstall java <version>
```

Additional Tips

SDKMAN can also manage other SDKs like Maven, Gradle, and Kotlin.
To update SDKMAN itself:
```
sdk update
```
To update all installed SDKs:
```
sdk upgrade
```

By following these steps, you can easily install, switch, and manage multiple Java versions using SDKMAN!